A design patterns are well-proved solution for solving the specific problem/task.
Now, a question will be arising in your mind what kind of specific problem? Let me explain by taking an example. Problem Given:
Suppose you want to create a class for which only a single instance (or
object) should be created and that single object can be used by all
other classes.
Solution: Singleton design pattern is the best solution of above specific problem. So, every design pattern has some specification or set of rules for solving the problems. What are those specifications, you will see later in the types of design patterns.
But remember one-thing, design patterns are programming language
independent strategies for solving the common object-oriented design
problems. That means, a design pattern represents an idea, not a
particular implementation.
By using the design patterns you can make your code more flexible,
reusable and maintainable. It is the most important part because java
internally follows design patterns.
To become a professional software developer, you must know at least
some popular solutions (i.e. design patterns) to the coding problems.
Advantage of design pattern:
They are reusable in multiple projects.
They provide the solutions that help to define the system architecture.
They capture the software engineering experiences.
They provide transparency to the design of an application.
They are well-proved and testified solutions since they have been
built upon the knowledge and experience of expert software developers.
Design patterns don?t guarantee an absolute solution to a problem.
They provide clarity to the system architecture and the possibility of
building a better system.
When should we use the design patterns?
We must use the design patterns during the analysis and requirement phase of SDLC(Software Development Life Cycle).
Design patterns ease the analysis and requirement phase of SDLC by providing information based on prior hands-on experiences.
Categorization of design patterns:
Basically, design patterns are categorized into two parts:
Core java (or JSE) Design Patterns.
JEE Design Patterns.
Core Java Design Patterns
In core java, there are mainly three types of design patterns, which are further divided into their sub-parts:
1.Creational Design Pattern
Factory Pattern
Abstract Factory Pattern
Singleton Pattern
Prototype Pattern
Builder Pattern.
2. Structural Design Pattern
Adapter Pattern
Bridge Pattern
Composite Pattern
Decorator Pattern
Facade Pattern
Flyweight Pattern
Proxy Pattern
3. Behavioral Design Pattern
Chain Of Responsibility Pattern
Command Pattern
Interpreter Pattern
Iterator Pattern
Mediator Pattern
Memento Pattern
Observer Pattern
State Pattern
Strategy Pattern
Template Pattern
Visitor Pattern
Creational design patterns
Creational design patterns are concerned with the way of creating objects.
These design patterns are used when a decision must be made at the time
of instantiation of a class (i.e. creating an object of a class).
But everyone knows an object is created by using new keyword in java. For example:
StudentRecord s1=new StudentRecord();
Hard-Coded code is not the good programming approach. Here, we are
creating the instance by using the new keyword. Sometimes, the nature of
the object must be changed according to the nature of the program. In
such cases, we must get the help of creational design patterns to
provide more general and flexible approach.
Types of creational design patterns
There are following 6 types of creational design patterns.
Factory Method Pattern
Abstract Factory Pattern
Singleton Pattern
Prototype Pattern
Builder Pattern
Object Pool Pattern
Factory Method Pattern
A Factory Pattern or Factory Method Pattern says that just define an interface or abstract class for creating an object but let the subclasses decide which class to instantiate. In other words, subclasses are responsible to create the instance of the class.
The Factory Method Pattern is also known as Virtual Constructor.
Advantage of Factory Design Pattern
Factory Method Pattern allows the sub-classes to choose the type of objects to create.
It promotes the loose-coupling by eliminating the need to
bind application-specific classes into the code. That means the code
interacts solely with the resultant interface or abstract class, so that
it will work with any classes that implement that interface or that
extends that abstract class.
Usage of Factory Design Pattern
When a class doesn't know what sub-classes will be required to create
When a class wants that its sub-classes specify the objects to be created.
When the parent classes choose the creation of objects to its sub-classes.
UML for Factory Method Pattern
We are going to create a Plan abstract class and concrete classes
that extends the Plan abstract class. A factory class GetPlanFactory is
defined as a next step.
GenerateBill class will use GetPlanFactory to get a Plan object. It
will pass information (DOMESTICPLAN / COMMERCIALPLAN /
INSTITUTIONALPLAN) to GetPalnFactory to get the type of object it needs.
Calculate Electricity Bill : A Real World Example of Factory Method
Step 1: Create a Plan abstract class.
import java.io.*; abstractclass Plan{ protecteddouble rate; abstractvoid getRate(); publicvoid calculateBill(int units){ System.out.println(units*rate); } }//end of Plan class.
Step 2: Create the concrete classes that extends Plan abstract class.
class DomesticPlan extends Plan{ //@override publicvoid getRate(){ rate=3.50; } }//end of DomesticPlan class.
class CommercialPlan extends Plan{ //@override publicvoid getRate(){ rate=7.50; } //end of CommercialPlan class.
class InstitutionalPlan extends Plan{
//@override
publicvoid getRate(){
rate=5.50;
}
/end of InstitutionalPlan class.
Step 3: Create a GetPlanFactory to generate object of concrete classes based on given information.
class GetPlanFactory{ //use getPlan method to get object of type Plan public Plan getPlan(String planType){ if(planType == null){ returnnull; } if(planType.equalsIgnoreCase("DOMESTICPLAN")) { returnnew DomesticPlan(); } elseif(planType.equalsIgnoreCase("COMMERCIALPLAN")){ returnnew CommercialPlan(); } elseif(planType.equalsIgnoreCase("INSTITUTIONALPLAN")) { returnnew InstitutionalPlan(); } returnnull; } }//end of GetPlanFactory class.
Step 4: Generate Bill by using the GetPlanFactory to get the object of concrete classes by passing an information such as
type of plan DOMESTICPLAN or COMMERCIALPLAN or INSTITUTIONALPLAN.
import java.io.*; class GenerateBill{ publicstaticvoid main(String args[])throws IOException{ GetPlanFactory planFactory = new GetPlanFactory(); System.out.print("Enter the name of plan for which the bill will be generated: "); BufferedReader br=new BufferedReader(new InputStreamReader(System.in)); String planName=br.readLine(); System.out.print("Enter the number of units for bill will be calculated: "); int units=Integer.parseInt(br.readLine()); Plan p = planFactory.getPlan(planName); //call getRate() method and calculateBill()method of DomesticPaln. System.out.print("Bill amount for "+planName+" of "+units+" units is: "); p.getRate(); p.calculateBill(units); } }//end of GenerateBill class.
The #pragma preprocessor directive is used to provide additional
information to the compiler. The #pragma directive is used by the
compiler to offer machine or operating-system feature.
Syntax:
#pragma token
Different compilers can provide different usage of #pragma directive.
The turbo C++ compiler supports following #pragma directives.
The advent of the digital marketing has opened up a novel landscape of doing business i.e. online business.
According to a
survey- by 2017, India will have around 600 million internet users that
ultimately create a fascinating business opportunity to sell services
and products to a growing population of tech-savvy internet users.
Recently, booming prevalence of digital India campaign is also adding
lots of new flavors and fervors to the future of digital marketing in
India. Growing startup trend is another reason that plays significant
role in creating a great scope of digital marketing in India. The most
common problem that startups face is lack of funds and digital marketing
can rescue them as the most cost-effective blessing in disguise. It is
highly economical and equally powerful way of conversion-oriented
marketing. All the digital marketing maneuvers can also be quantified
through powerful digital marketing tools like Kissmetrics, Google
Analytics, Google Website Optimizer, etc. that make it one of the most
result-oriented modes of marketing.
There are more
than 900 private TV channels and 250+ radio stations in India, which
make traditional marketing quite expensive and highly confusing with
lots of in-built vacillations. However, in today’s world of internet,
Digital Marketing is the only one and most guaranteed way of marketing,
which is popularly being the most preferred space of marketing
communications and related interactions.
Changing statistical dynamics of future of Digital Marketing in India are-
The future of
marketing is way beyond the traditional marketing or outbound marketing
methodologies that have been using TV and radio ads, print ads,
hoardings, banners, magazines, etc. Now, marketing is majorly based on
online marketing (inbound marketing) — Marketing in the Digital Sphere.
Scope of Digital Marketing provides some of the most powerful techniques
of marketing where traditional modes of marketing fail.
Digital Marketing has
great panjandrum over entrepreneurs as it not only rescues but also
empowers them to optimize their startups in the most cost-effective and
quickest possible fashion. Future of digital marketing is going to be
more encompassing in 2017, thanks to its ability to offer wide range of
economical, powerful and contemporary mechanisms and mediums of
marketing.
Digital marketing takes things into consideration like –
Page rankings in search engine results
Advertising on search engine platforms
Conversion through SMO & SEO campaigns
Optimization of internet marketing & associated ROI
Banner ads on other websites & Marketing on Digital World
Key findings of some of the Recent Digital Marketing Surveys are –
34% of the companies already had an integrated digital marketing strategy in 2016
72% marketers believe that traditional model of marketing is no longer sufficient
Company revenue driven by internet marketing will get increased by 30%
In 2017, 80% businesses will increase their digital marketing budget
Digital Marketing budget may surpass the IT budget in 2017
Future Trends of Digital Marketing in India
Digital Marketing
will remain as the most powerful and result-oriented way of marketing in
2017 too, and some of my observations on current and future outlook of 5
key channels that will pay key role in deciding future of digital
marketing in India are–
1. Mobile Marketing
To devise
result-oriented marketing plans and campaigns, mobile marketing is going
to play one of the most significant roles in 2017. Understanding
customers’ changing needs and characteristics lets marketers plan in a
result-oriented fashion. As per stats-
Current Outlook of Mobile Marketing in Driving Customer-Engagement- 40% (approx)
Future Outlook of Mobile Marketing in Driving Customer-Engagement- 75% (approx)
From consumers’
device usage perspective, Smartphone adoption and prevalence of mobile
apps and messaging are going to be the topmost trends of digital
marketing in 2017. From Facebook’s Mobile Messenger, to Whatsapp and
WeChat, we have been witnessing the growing wish of consumers to
communicate directly through mobiles compared to public social network
pages. 2017 will come with some of the new options for paid media on
mobile messaging apps that will further be boosted by artificial
intelligence, which is another trend that will go hand in hand with
mobile marketing. Brands are developing bots to engage customers, and
Facebook’s Bot Engine for Messenger and Google’s new assistance service
introduced in Google I/O 2016 indicated towards the rise of Artificial
Intelligence to provide more personalized and interactive assistance to
consumers through mobile marketing.
More than 52% of searches are done through mobile.
89% of Facebook Daily Active users come through mobile.
83% of Facebook advertising revenue comes through Smartphones.
92% of mobile media time is spent in Smartphone apps by consumers.
Modern customers
prefer to view a video content on company promos. Growing need for the
visual content has turned video marketing be one of the most appealing
trends of digital marketing in 2017. When a visual content is well
produced to communicate the message in an interactive and engaging way,
conversions are always guaranteed.
Current Outlook of Video Marketing in driving Customer Engagement- 37%
Future Outlook of Video Marketing in driving Customer Engagement- 69%
Video content is
swallowing up the content marketing and online marketers take advantage
of its power to tempt more customers in quickest possible time. With
booming mobile marketing, videos are now offered on mobile phones that
fuel up the whole process. Video marketing is the most powerful way that
companies use for –
Introducing themselves
Spreading their messages
Promoting their products/services
Increasing their reach and optimizing search ranking
Boosting customer engagement and enhancing returns on investments
Different kinds of Trending Video Content are-
Social Media Videos like Facebook Videos, Facebook 360 Videos, YouTube Videos, Snapchat Videos, etc.
Use of GIF videos on different social media channels like Twitter & Facebook
Product Description/Demo Videos and Landing Page Videos
Storytelling with the help of live streaming videos
Use of Videos in Email Marketing
3. Email Marketing
Email marketing is so
effective in nurturing leads and ensuring conversions. Email marketers
of some of the most successful marketing agencies claim a return of $40
for every dollar they invested. Well-targeted email marketing will be
one of the most effective ways of ensuring conversions in 2017.
Current Outlook of Email Marketing in Driving Customer Engagement- 45%
Future Outlook of Email Marketing in Driving Customer Engagement- 57%
Email marketing is
the most important part of your business branding and you need to choose
those trends that befit with your customer profile and business
objective. Your emails should reflect your quality and using
professional email templates should be the base of your e-mail marketing
campaign in 2017. Some of the top trends of email marketing in 2017
are-
Use
of Email automation tools for sending and tracking of targeted and
personalized emails that will let you understand more and more about
your customer base like their demographics, tendencies, age, loyalty,
etc.
Integration
of social media content in email marketing strategy is another trend
that will see great rise in 2017. Marketers will preferably provide
references to their social content within their emails.
2017
will see a decrease in email blast, as this year would be of customized
mails. Mobile-friendly email marketing is another trend that will be
quite popular within the domains of digital marketing.
Aesthetically
appealing animated emails are also going to be a popular trend of
digital marketing as such fun new mails entice visitors and hold their
attention that ultimately aids in conversions.
4. Social Media Marketing
Social media changes
quickly as there are dozens of new platforms arrive each year. The year
2017 will also be a host for the variety of new social media trends, and
social media marketing will for sure be one of the most popular digital
marketing channels for branding, optimization, lead generations and
conversions.
Current Outlook of Social Media Marketing in Driving Customer Engagement- 36%
Future Outlook of Social Media Marketing in Driving Customer Engagement- 55%
As social media keeps
evolving, it has a massive power to channelize marketing campaigns in
innovative and effective ways. Social media is a medium that adeptly
responds to new tech innovations, but at the same time, it also exceeds
customer’s expectations. Knowing future trends of social media and
planning strategy as per that will ensure success for companies. Some of
the key social media trends in 2017 are –
Enormous
evolution of Snapchat is going to be one of the most interesting,
powerful and creative trends of social media marketing in 2017.
Live
video streaming is slowly changing the scenario of social media
campaigns, and the trend will see great rise in next year too. Different
platforms like Facebook live, SnapChat, Twitter, and Instagram all are
blending live streaming videos that will let them be a top pick for
marketers.
Live
videos also ensure 10 times more comments than pre-recorded videos, and
such qualities will let them dominate social media marketing more
efficaciously
Instagram stories, social slideshow ads, social chats, etc. would be the top components of social media marketing in 2017.
5. Search & SEO Marketing
Search engines evolve
constantly, and their changes prompt shift in marketers’ ways of
targeting audiences. To succeed, it is important for you to know latest
changes of SEO marketing and employing effective search engine
strategies accordingly. Mobile marketing and social media optimization
has enhanced the frequencies of searches all across the globe, and as
per statistics, 14 billion web searches are conducted each month through
different search engines.
Current Outlook of SEO Marketing in driving Customer Engagement- 21%
Future Outlook of SEO Marketing in driving Customer Engagement- 40%
Some of the SEO trends that will turn out to be major hits in 2017 are-
Link
building will stay as a powerful SEO technique, mobile marketing will
rock the house, and along with Google, other search engines will also
play significant roles in ensuring great search results.
Use
of keyword search tools like Google’s Keyword Planner, Moz’s keyword
Planner are going to be the most effective trends to know right keywords
that your audiences search.
Quality
content marketing with perfect blending of video content would be
another prudent practice that experts think as the most dominant future
trend of digital marketing in 2017.
Personalizing
SEO campaigns as per target audiences, being creative, use of natural
links and moving site to HTTPS will be the SEO trend that will decide
future of internet marketing campaigns in 2017.
Conclusion
To survive in today’s
competitive and frenzied market scenario; it is must for Indian
businesses to have a well-integrated internet marketing strategy.
Without Digital Marketing, businesses may fall short of creating
contemporary marketing strategies and hence, they may turn directionless.
Digital Marketing is the present and the future of marketing that will
not only let businesses survive but also thrive in the most
result-oriented fashion. Including new techniques, following latest
updates of Google and incorporating future trends of digital marketing
will let your inbound marketing reap great benefits for you in 2017.
In the year 2016, most of the industries were kind of struggling with
a growth rate around 6 to 11%; only digital industry saw a growth rate
of 41%, which is not going to be stagnant in 2017 as well. Digital
Marketing will for sure remain as the most effective way of marketing in
the future too, and it will be worthwhile for you to climb on to the
digital bandwagon when the time is right, either career-wise or
business-wise.
Double-DES is two successive DES instances, while Triple-DES is three successive DES instances.
Use 3DES and not 2DES because 2DES does not yield the security
increase that you would believe. Namely, 2DES uses 112 key bits (two
56-bit DES keys) but offers a security level of about 257, not 2112, because of a "meet-in-the middle attack" which is well explained there
(not to be confused with "man-in-the-middle", a completely different
concept). Similarly, 3DES uses 168 key bits, but offers "only" 2112
security (which is quite sufficient in practice). This also explains
why 3DES is sometimes used with a 112-bit key (the third DES key is a
copy of the first): going to 168 bits does not actually make things more
secure.
This can be summarized as: we use n-DES because a simple DES is too weak (a 56-bit key can be brute-forced by a determined attacker), but in order to really improve security, we must go to n ≥ 3.
Of course, every additional DES implies some computational overhead
(simple DES is already quite slow in software, 3DES thrice as much).
Cloud computing is steadily becoming a popular and cheaper option for
most IT-reliant companies for various integral services to their
operations. What used to be investments for servers, hardware and
storage devices are now monthly service fees for virtual storage and
applications that a network of computers can access anytime and anywhere
with the right IT infrastructure.
Although
the emergence of great cloud-based computing companies like RingCentral
and Dropbox that provide awesome services is such a treat for SMEs and
startups, the way the technology is structures presents various issues
that need to be addressed.
These issues include but are not limited to the following:
Security
Since
the data isn’t protected by security measures you employed yourself,
how sure can you be that the cloud computing company you contracted is
taking every measure to keep it safe? And who are they keeping it safe
from? The data itself is stored on the service provider’s own
infrastructure. You pay them to store it and manage it, along with
giving you a way to access and change the data. But how about the people
who access it illegally? How does your service provider prevent this?
Since the service provider hosts the data, is it allowed access to it,
or must it simply facilitate your usage? Before you ump headfirst into
the trend, make sure you ask your service provider what it does to
secure the data you upload.
Tampering
In
relation to data security, your data may be tampered while it is under
the purview of your service provider’s infrastructure. While the data
may not be taken or deleted, it can be changed or modified.
Data ownership
The
transference of data to servers that aren’t physically-owned by the
authors or uploaders of the data themselves begs the question of whom
does the data belong to? Lawmakers continue to debate and try to define
the parameters of the data stored in the cloud as to whose the pieces
are, or if it’s actually owned by no one.
Impact on other industries
VoIP
phone services are basically telephony solutions that work through
software phones and access to cloud-based computing services and
applications. The great price difference from a landline phone system
may impact the PSTN-based companies greatly when users switch to
digitized and cheaper systems, creating more jobs but turning others
almost obsolete. Although this move into the future may be favorable,
old systems become outdated. New courses in education may emerge from
the shift while others that involve older technology may not be taught
anymore.
So if you’re planning to switch to internet-based
services for storing your files, making phone calls or collaborating on a
project, consider the risks and issues that face this exciting new tech
first before you decide it’s time for you to enter the future.
Not all cloud platforms are the same. Application developers have
become increasingly savvy about the cloud and the options now available
to them. But most of today’s cloud solutions are essentially
“one-size-fits-all,” requiring developers to sacrifice one, or more,
aspects of their cloud computing requirements – whether it's cost,
preferred provider or availability of certain services to meet their
unique needs.
While practically everything is being offered “as-a-service” now,
vendors’ offerings can vary wildly as they try to adapt to the evolving
needs of applications. Some apps are simple, others have complex
platform requirements. Most apps need to scale, but some have limited
life spans. How exactly can developers find a cloud platform that is a
good fit for their needs today, but will adapt to meet changing needs?
Answering that question may seem daunting at first, but if you
consider the following five criteria when evaluating cloud providers,
you’ll be more confident that you’re selecting the right cloud platform.
Polytech – Can the Platform Support Multiple Languages, Databases and Middleware?
You may need to use multiple languages or databases as you create
your applications. Each application will have different needs as it is
developed, and those needs also may change over time. By finding a cloud
provider that can support multiple languages and databases, you’ll
avoid having to select a different cloud for each type of application.
It’s important not just to look at the service a cloud provider is
offering, but whether that platform provides the depth and breadth you
need.
For example, a SaaS company that helps developers build visual
prototypes in the cloud leverages several PHP frameworks, as well as a
variety of databases and queueing technologies to meet its clients’
varying needs. And a sport merchandise company uses multiple languages
and related frameworks and middleware to power its site to ensure
customers can shop anytime.
Polycloud – Can the Provider Run on Multiple Infrastructures and Support Hybrid Options?
As demand increases for your applications, you’ll need a provider
that can grow with you. The key to ensuring compatibility with these
changing requirements is not getting locked in. Therefore you should
look for a PaaS solution that supports multiple infrastructures and
offers the combination of both private and public resources in hybrid
cloud configurations.
For example, by deploying high availability and disaster recovery
(HA/DR) across public clouds, one e-commerce company ensures its
independent artists and designers can showcase their work without
interruption. A gamification company separates its data and application
infrastructures by deploying them on different public clouds with a low
latency secure gateway for inter-cloud connectivity.
Complete Application Lifecycle Support – Can the Platform Deliver a Balance of Automation and Granular Control?
Your company’s current IT processes and the size of your DevOps team
will likely guide the level of automation or extent of control you want.
As you’re considering your cloud platform, you will want to make sure
that it can provide, both, a high level of automation and granular
control, so you are not locked in to your initial choice.
For example, a start-up may have a great idea for an app, but few
employees in DevOps. In this scenario, automation is necessary to enable
the small staff to write the code and easily deploy the app. But over
time, as the company grows and scales, their applications may become
more complex and require greater control. On the flipside, there are
large enterprises that have historically managed in-house
infrastructure, but now want the benefits of moving to the cloud. They
often want a platform that provides the same level of control they are
accustomed to, with more automation.
Proven – Does the Cloud Provider Have a Strong Track Record?
Because the cloud market is relatively new with strong growth
potential, there are a myriad of young platform providers that are
trying to get in on the opportunity. When considering cloud platform
providers, it’s critical to choose a stable company that can provide the
service level you need, whether you’re a small start-up, a development
agency supporting many customers or running large enterprise
applications. You should look for case studies and references that prove
the provider’s capabilities, and strongly consider selecting a provider
with a history of delivering a commercial-grade platform that is
reliable, secure and flexible.
Questions you should ask include: how long has the company been in
business, how many apps they have in production, what’s the expertise of
both the management and development team, and are they comfortable with
both legacy and new apps. With these answers, you won’t risk your
business-critical applications to an inexperienced provider that has
service interruptions, poor support, and could unexpectedly go out of
business.
Customer Support - How Involved Does Your Provider Get?
Many cloud platform providers offer basic help through a knowledge
base or other online resources. That is often where the support ends,
but it doesn’t have to. Some providers are investing heavily in enhanced
customer support. They employ experts who can help you speed your time
to market and focus on developing and troubleshooting apps without
having to hire more Ops staff. They provide advice on deployment, high
availability strategies, scaling, code and security audits, application
analysis and best practices. They will stay with you even after your app
launches, not just reacting to problems, but providing proactive
monitoring and support that keeps your apps running smoothly 24x7.
One financial services organization, for example, relies on its cloud
provider’s expertise and dedicated support team for round-the-clock
availability and scaling. With this assistance, its developers can focus
on their core strengths while the cloud provider takes care of all
DevOps responsibilities.
Cloud platforms are dramatically changing the ways that apps are
developed and deployed. So that you can focus on what you do best –
developing apps – you need a platform provider who will not lock you
into decisions that may hamper your innovation and growth over the long
term. Clearly, the underlying platform is critical, but equally
important is the flexibility and level of support that a cloud provider
can deliver. By considering these five criteria, you can find a provider
that will enable you to leverage its platform to plan, build, deploy
and manage your applications throughout the entire lifecycle of your
business and effectively innovate for the future. Are these the criteria
your company has used when selecting a cloud platform? What other
factors have you considered in your decision-making process?
Many
organizations embark on cloud migrations to achieve scalability,
cost-efficiency and higher application performance. But migrating apps
to the cloud is a complex process that requires careful planning and
deliberation.
It's essential that organizations consider all possibilities -- both
good and bad. Cloud migration issues, such as unexpected costs,
interoperability, security gaps and unanticipated application rework,
can create significant obstacles. To help smooth a frequently bumpy
path, organizations need to craft a well-thought-out migration strategy.
Whether your organization is migrating to the cloud from an in-house
environment or from one cloud to another, it's important to understand
the process and temper any exorbitant expectations. And, since not every
application will benefit from the cloud, make sure a migration is right
for your organization before diving in.
1.Planning for a cloud migration
Prepare to take the cloud plunge with a migration strategy
Cloud migrations can be fraught with risks and unknowns, so don't
go into them unprepared. To avoid potential disaster, map out your
strategy and plan for the unexpected. A solid migration strategy acts as
a guide or checklist to ensure a successful journey to the cloud.
Enterprises need to plan for expenses -- especially the unexpected ones
-- as well as the migration's effect on an organization, its systems and
users.
2. Performing a cloud migration
Technical considerations for migrating to the cloud
Cloud migrations can be laborious, requiring many steps and manual
adjustments. While a solid cloud migration strategy can simplify the
process, enterprises still need to consider a number of factors,
including tools, governance, performance, application design and more.
With a plethora of third-party tools available, it's important to
identify those that best meet your migration needs. Additionally,
enterprises must consider scary, what-if scenarios, such as a migration
driving up, rather than reducing, application costs.
3.Avoiding cloud migration risks
Mitigating migration challenges for cloud success
The path to cloud computing can be a long and arduous one for
organizations considering migration. Whether an enterprise is migrating
from an on-premises environment or from one cloud to another, it's a
risky proposition. Enterprises often contend with regulatory and
compliance issues, unexpected budget busters, poor performance, security
concerns and more. But for many organizations, improved scalability,
agility and other cloud benefits make the risk worth the reward.
Explanation: p is a pointer to a "constant integer". But we tried to change the value of the "constant integer".
C aptitude 1.2
main()
{
chars[ ]="man";
inti;
for(i=0;s[ i ];i++)
printf("\n%c%c%c%c",s[ i ],*(s+i),*(i+s),i[s]);
}
Explanation: s[i], *(i+s), *(s+i), i[s] are all different ways of
expressing the same idea. Generally array name is the base address for
that array. Here s is the base address. i is the index
number/displacement from the base address. So, indirecting it with * is
same as s[i]. i[s] may be surprising. But in the case of C it is same
as s[i].
Elastic Beanstalk is a Platform As A Service (PaaS) that streamlines
the setup, deployment, and maintenance of your app on Amazon AWS. It’s a
managed service, coupling the server (EC2), database (RDS), and your
static files (S3). You can quickly deploy and manage your application,
which automatically scales as your site grows. Check out the official documentation for more information.
Getting Started
We’ll be using a simple “Image of the Day” app, which you can grab from this repository:
After you download the code, create a virtualenv and install the requirements via pip:
$ pip install -r requirements.txt
Next, with PostgreSQL running locally, set up a new database named iotd. Also, depending upon your local Postgres configuration, you may need to update the DATABASES configuration in settings.py. For example, I updated the config to:
Navigate to the admin page in your browser at http://localhost:8000/admin and add a new image, which will then be displayed on the main page.
The application isn’t meant to be very exciting; we’re just using it
for demo purposes. All it does is let you upload an image via the admin
interface and display that image full screen on the main page. That
said, although this is a relatively basic app, it will still allow us to
explore a number of “gotchas” that exist when deploying to Amazon
Beanstalk and RDS.
Now that we have the site up and running on our local machine, let’s start the Amazon deployment process.
CLI for AWS Elastic Beanstalk
To work with a Amazon Elastic Beanstalk, we can use a package called awsebcli. As of this writing the latest version of is 3.7.4 and the recommended way to install it is with pip:
$ pip install awsebcli
Now test the installation to make sure it’s working:
$ eb --version
This should give you a nice 3.x version number:
EB CLI 3.7.4 (Python 3.4.3)
To actually start using Elastic Beanstalk you will need an account with AWS (surprise!). Sign up (or log in).
Configure EB – initialize your app
With the AWS Elastic Beanstalk CLI working, the first thing we want
to do is create a Beanstalk environment to host the application on. Run
this from the project directory (“image-of-the-day”):
$ eb init
This will prompt you with a number of questions to help you configure your environment.
Default region
Choosing the region closest to your end users will generally provide the best performance.
Credentials
Next, it’s going to ask for your AWS credentials.
Here, you will most likely want to set up an IAM User. See this guide
for how to set one up. If you do set up a new user you will need to
ensure the user has the appropriate permissions. The simplest way to do
this is to just add “Administrator Access” to the User. (This is
probably not a great choice for security reasons, though.) For the
specific policies/roles that a user needs in order to create/manage an
Elastic Beanstalk application, see the link here.
Application name
This will default to the directory name. Just go with that.
Python version
Next, the CLI should automagically detect that you are using Python
and just ask for confirmation. Say yes. Then you need to select a
platform version. You have 2 different options here for Python 3:
Python 3.4
Python 3.4 (Preconfigured – Docker)
If you’re a hipster, choose the ‘Preconfigured – Docker’ choice,
otherwise go with the normal ‘Python 3.4’. No, only teasing; the basic
difference is this:
Python 3.4
This gives you an EC2 image running 64bit Amazon Linux with Python
3.4 pre-installed. The front end web server is apache, with mod_wsgi
installed. This is the “standard” or “traditional” way that Beanstalk
works. In other words, with this option Beanstalk will create EC2 images
for you, and you can use the ebextension files we will talk about later to customize the EC2 image.
Python 3.4 (Preconfigured – Docker)
This gives you an EC2 image running Docker, with a Docker image
already setup for you. The Docker image runs 64bit Debian Jessie with
Python 3.4, nginx 1.8 and uWSGI 2.0.8. Because you’re basically
interacting with the Docker image directly, if you choose this route you
would use standard Docker configuration techniques (i.e., a
‘Dockerfile’), and then you don’t have to do much that is AWS Beanstalk
specific, as Beanstalk knows how to manage the Docker image for you.
For this article we will focus on the “standard” or “traditional” way
of using an EC2 image, so choose the ‘Python 3.4’ option and let’s move
on.
SSH
Say yes to setting up SSH for your instances.
RSA Keypair
Next, you need to generate an RSA keypair, which will be added to your ~/.ssh
folder. This keypair will also be uploaded to the EC2 public key for
the region you specified in step one. This will allow you to SSH into
your EC2 instance later in this tutorial.
What did we accomplish?
Once eb init is finished, you will see a new hidden folder called .elasticbeanstalk in your project directory:
Inside that directory is a config.yml file, which is a configuration file that is used to define certain parameters for your newly minted Beanstalk application.
At this point, if you type eb console it will open up
your default browser and navigate to the Elastic Beanstalk console. On
the page, you should see one application (called image-of-the-day if you’re following along exactly), but no environments.
An application represents your code application and is what eb init
created for us. With Elastic Beanstalk, an application can have
multiple environments (i.e., development, testing, staging, production).
It is completely up to you how you want to configure/manage these
environments. For simple Django applications I like to have the
development environment on my laptop, then create a test and a
production environment on Beanstalk.
Let’s get a test environment set up…
Configure EB – create an environment
Coming back to the terminal, in your project directory type:
$ eb create
Just like eb init, this command will prompt you with a series of questions.
Environment Name
You should use a similar naming convention to what Amazon suggests –
e.g., application_name-env_name – especially when/if you start hosting
multiple applications with AWS. I used – iod-test.
DNS CNAME prefix
When you deploy an app to Elastic Beanstalk you will automatically get a domain name like xxx.elasticbeanstalk.com. DNS CNAME prefix is what you want to be used in place of xxx.
The default probably won’t work if you’re following along because
somebody else has already used it (the names are global to AWS), so pick
something unique and keep on going.
What happens now?
At this point eb will actually create your environment for you. Be patient as this can take some time.
If you do get an error creating the environment, like – aws.auth.client.error.ARCInstanceIdentityProfileNotFoundException–
check that the credentials you are using have appropriate permissions
to create the Beanstalk environment, as discussed earlier in this post.
Also, it may prompt you with a message about Platform requires a service role. If it does, just say yes and let it create the role for you.
Immediately after the environment is created, eb will attempt to deploy your application, by copying all the code in your project directory to the new EC2 instance, running pip install -r requirements.txt in the process.
You should see a bunch of information about the environment being set up displayed to your screen, as well as information about eb trying to deploy. You will also see some errors. In particular you should see these lines buried somewhere in the output:
ERROR: Your requirements.txt is invalid. Snapshot your logs for details.
Don’t worry – It’s not really invalid. Check the logs for details:
$ eb logs
This will grab all the recent log files from the EC2 instance and
output them to your terminal. It’s a lot of information, so you may want
to redirect the output to a file (eb logs -z). Looking through the logs, you’ll see one log file named eb-activity.log:
Error: pg_config executable not found.
The problem is that we tried to install psycopy2 (the
Postgres Python bindings), but we need the Postgres client drivers to be
installed as well. Since they are not installed by default, we need to
install them first. Let’s fix that…
Customizing the Deployment Process
eb will read custom .config files from a folder called “.ebextensions” at the root level of your project (“image-of-the-day” directory). These .config
files allow you to install packages, run arbitrary commands and/or set
environment variables. Files in the “.ebextensions” directory should
conform to either JSON or YAML syntax and are executed in alphabetical order.
Installing packages
The first thing we need to do is install some packages so that our pip install command will complete successfully. To do this, let’s first create a file called .ebextensions/01_packages.config:
EC2 instances run Amazon Linux, which is a Redhat flavor, so we can use yum
to install the packages that we need. For now, we are just going to
install three packages – git, the Postgres client, and libjpeg for
Pillow.
After creating that file to redeploy the application, we need to do the following:
We have to commit the changes because the deployment command eb deploy
works off the latest commit, and will thus only be aware of our file
changes after we commit them to git. (Do note though that we don’t have
to push; we are working from our local copy…)
As you probably guessed, the next command is:
$ eb deploy
You should now see only one error:
INFO: Environment update is starting.
INFO: Deploying new version to instance(s).
ERROR: Your WSGIPath refers to a file that does not exist.
INFO: New application version was deployed to running EC2 instances.
INFO: Environment update completed successfully.
Let’s find out what’s happening…
Configuring our Python environment
EC2 instances in Beanstalk run Apache, and Apache will find our
Python app according to the WSGIPATH that we have set. By default eb assumes our wsgi file is called application.py. There are two ways of correcting this-
Option 1: Using environment-specific configuration settings
$ eb config
This command will open your default editor, editing a configuration file called .elasticbeanstalk/iod-test.env.yml. This file doesn’t actually exist locally; eb
pulled it down from the AWS servers and presented it to you so that you
can change settings in it. If you make any changes to this pseudo-file
and then save and exit, eb will update the corresponding settings in your Beanstalk environment.
If you search for the terms ‘WSGI’ in the file, and you should find a configuration section that looks like this:
And then you will have you WSGIPath set up correctly. If you then save the file and exit, eb will update the environment configuration automatically:
Printing Status:
INFO: Environment update is starting.
INFO: Updating environment iod-test's configuration settings.
INFO: Successfully deployed new configuration to environment.
INFO: Environment update completed successfully.
The advantage to using the eb config method to change
settings is that you can specify different settings per environment. But
you can also update settings using the same .config files that we were using before. This will use the same settings for each environment, as the .config files will be applied on deployment (after the settings from eb config have been applied).
Option 2: Using global configuration settings
To use the .config file option, let’s create a new file called /.ebextensions/02_python.config:
DJANGO_SETTINGS_MODULE: "iotd.settings" – adds the path to the settings module.
"PYTHONPATH": "/opt/python/current/app/iotd:$PYTHONPATH" – updates our PYTHONPATH so Python can find the modules in our application. This path may vary depending on your setup!
WSGIPath: iotd/iotd/wsgi.py sets our WSGI Path.
NumProcesses: 3 and NumThreads: 20 – updates the number of processes and threads used to run our WSGI application.
Again, we can do a git commit then an eb deploy to update these settings.
Next let’s add a database.
Configuring a Database
Try to view the deployed website:
$ eb open
This command will show the deployed application in your default browser. You should see a connection refused error:
OperationalError at /could not connect to server:Connection refusedIs the server running on host "localhost" (127.0.0.1) and acceptingTCP/IP connections on port 5432?
This is because we haven’t set up a database yet. At this point eb will set up your Beanstalk environment, but it doesn’t set up RDS (the database tier). We have to set that up manually.
Database setup
Again, use eb console to open up the Beanstalk configuration page.
From there, do the following:
Click the “Configuration” link.
Scroll all the way to the bottom of the page, and then under the
“Data Tier” section, click the link “create a new RDS database”.
On the RDS setup page change the “DB Engine” to “postgres”.
Add a “Master Username” and “Master Password”.
Save the changes.
Beanstalk will create the RDS for you. Now we need to get our Django
app to connect to the RDS. Beanstalk will help us out here by exposing a
number of environment variables on the EC2 instances for us that detail
how to connect to the Postgres server. So all we need to do is update
our settings.py file to take advantage of those environment variables. Confirm that the DATABASES configuration parameter reflects the following in settings.py:
This simply says, “use the environment variable settings if present, otherwise use our default development settings.” Simple.
Handling database migrations
With our database setup, we still need to make sure that migrations
run so that the database table structure is correct. We can do that by
modifying .ebextensions/02_python.config and adding the following lines at the top of the file:
container_commands allow you to run arbitrary commands
after the application has been deployed on the EC2 instance. Because the
EC2 instance is set up using a virtual environment, we must first
activate that virtual environment before running our migrate command.
Also the leader_only: true setting means, “only run this command on the first instance when deploying to multiple instances.”
Don’t forget that our application makes use of Django’s admin, so we are going to need a superuser…
Create the Admin User
Unfortunately createsuperuser doesn’t allow you to specify a password when using the --noinput option, so we will have to write our own command. Fortunately, Django makes it very easy to create custom commands.
Create the file iotd/images/management/commands/createsu.py:
This file will allow you to run python manage.py createsu,
and it will create a superuser without prompting for a password. Feel
free to expand the command to use environment variables or another means
to allow you to change the password.
Once you have the command created, we can just add another command to our container_commands section in .ebextensions/02_python.config:
Make sure you commit the www directory to git so the static dir can be created. Then run eb deploy again, and you should now be in business:
INFO: Environment update is starting.
INFO: Deploying new version to instance(s).
INFO: New application version was deployed to running EC2 instances.
INFO: Environment update completed successfully.
At this point you should be able to go to http://your_app_url/admin, log in, add an image, and then see that image displayed on the main page of your application.
Success!
Using S3 for Media Storage
With this setup, each time we deploy again, we will lose all of our uploaded images. Why? Well, when you run eb deploy,
a fresh instance is spun up for you. This is not what we want since we
will then have entries in the database for the images, but no associated
images. The solution is to store the media files in Amazon Simple
Storage Service (Amazon S3) instead of on the EC2 instance itself.
Since there are good write ups on this already, I’ll just point you to my favorite: Using Amazon S3 to store you Django Static and Media Files
Apache Config
Since we are using Apache with Beanstalk, we probably want to set up
Apache to (among other things) enable gzip compression so files are
downloaded faster by the clients. That can be done with container_commands. Create a new file .ebextensions/03_apache.config and add the following:
Then you need to create the file .ebextensions/enable_mod_deflate.conf:
# mod_deflate configuration<IfModule mod_deflate.c># Restrict compression to these MIME typesAddOutputFilterByType DEFLATE text/plainAddOutputFilterByType DEFLATE text/htmlAddOutputFilterByType DEFLATE application/xhtml+xmlAddOutputFilterByType DEFLATE text/xmlAddOutputFilterByType DEFLATE application/xmlAddOutputFilterByType DEFLATE application/xml+rssAddOutputFilterByType DEFLATE application/x-javascriptAddOutputFilterByType DEFLATE text/javascriptAddOutputFilterByType DEFLATE text/css# Level of compression (Highest 9 - Lowest 1)DeflateCompressionLevel 9# Netscape 4.x has some problems.BrowserMatch ^Mozilla/4 gzip-only-text/html# Netscape 4.06-4.08 have some more problemsBrowserMatch ^Mozilla/4\.0[678] no-gzip# MSIE masquerades as Netscape, but it is fineBrowserMatch \bMSI[E] !no-gzip !gzip-only-text/html<IfModule mod_headers.c># Make sure proxies don't deliver the wrong contentHeader append Vary User-Agent env=!dont-vary</IfModule></IfModule>
Doing this will enable gzip compression, which should help with the
size of the files you’re downloading. You could also use the same
strategy to automatically minify and combine your CSS/JS and do any
other preprocessing you need to do.
Troubleshooting
Don’t forget the very helpful eb ssh command, which will
get you into the EC2 instance so you can poke around and see what’s
going on. When troubleshooting, there are a few directories you should
be aware of:
/opt/python – Root of where you application will end up.
/opt/python/current/app – The current application that is hosted in the environment.
/opt/python/on-deck/app – The app is initially put in on-deck and then, after all the deployment is complete, it will be moved to current. If you are getting failures in your container_commands, check out out the on-deck folder and not the current folder.
/opt/python/current/env – All the env variables that eb will set up for you. If you are trying to reproduce an error, you may first need to source /opt/python/current/env to get things set up as they would be when eb deploy is running.
opt/python/run/venv – The virtual env used by your application; you will also need to run source /opt/python/run/venv/bin/activate if you are trying to reproduce an error.
