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Q11. What are wrapper classes ?

Ans. They are wrappers to primitive data types. They allow us to access primitives as objects.

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Q12. what is the use of cookie and session ? and What is the difference between them ?

Ans. Cookie and Session are used to store the user information. Cookie stores user information on client side and Session does it on server side. Primarily, Cookies and Session are used for authentication, user preferences, and carrying information across multiple requests. Session is meant for the same purpose as the cookie does. Session does it on server side and Cookie does it on client side. One more thing that quite differentiates between Cookie and Session. Cookie is used only for storing the textual information. Session can be used to store both textual information and objects.

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Frequently asked. Among first few questions in the J2EE segment of interview.

Q13. What is deployment descriptor ?

or

What is the use of deployment descriptor ?

Ans. Deployment Descriptor which is usually web.xml is used to specify the classes, resources and configuration of the application and how the web server uses them to serve web requests.This file is usually added to WEB-INF folder and contains following

* Servlet entries and url mapping
* Plugins
* Some info regarding authentication / filters
* Landing Page
* Event Handlers

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Q14. Design an e commerce application using AWS ? What AWS services will you use ?

Amazon Web Services (AWS)

Ans. CloudFront for Static Media and cached content
EC2 and EKS ( Docker ) for main application computing
RDS and DynamoDB for Database
Lambda ( computing ) for running back end cron jobs
Kinesis for streaming and SQS for queuing
CloudWatch for Monitoring
CloudFormation for Infrastructure templating
S3 for Object Storage

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Q15. Difference between Region , Availability zone and Edge Locations ?

Amazon Web Services (AWS)

Ans. A Region is a Geographical entity like US-East , US-West etc. Each Region may have multiple availability zones where each zone comprise of 1 or more Data Center located with each other.

Edge Locations are the sites that hosts cached content for faster delivery and for saving network traffic as they feed content from sites that are local or near to consumption.

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Q16. What are the different S3 storage Tiers ?

Amazon Web Services (AWS)

Ans. S3 Standard
S3 IA - Infrequently Accessed
S3 One Zone IA - One Zone only , Infrequently Accessed
S3 Glacier - achieved

S3 Standard is most expensive , Glacier is least expensive

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Q17. What are the factors on which customers are charged for using S3 ?

Amazon Web Services (AWS)

Ans. Storage Tier ( IA , Standard , Glacier etc )
Storage ( Volume of Data )
No of Requests
Meta Data
Data Transfer Speed acceleration through cache and Edge Location

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Q18. What are the factors on which price classes are based on in case of EC2, S3, CloudFront and EBS ?

Amazon Web Services (AWS)

Ans. EC2 - Time and Reservation , Instance Type ( Memory , Computation power )
S3 - Accessibility Frequency , Data Transfer , Storage Space
CloudFront - Geography, No of Locations
EBS - IOPS, Access Frequency

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Q19. What are the different Route53 routing policies ?

Amazon Web Services (AWS)

Ans. Simple
Weighted
Latency
Failover
GeoLocation
Multivalue

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Q20. What is the relationship between VPC and subnet ? Can you tell with an example ?

Ans. A VPC is devided into multiple subnets. Subnet in a particular VPC could be public or private.

For Example - A particular account may have multiple vpc's for each of the business type. For each Business or VPC , One can have different subnets to cater to each department so that access across departments could be restricted. But still there could be identities that have control over different subnets. Moreover we could have multiple subnets for each department so as to have distinguished public and private networks having different types of applications ( public facing or internal consumption )

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Q21. Is Apache an application or Web server ?

Ans. Web server.

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Q22. Difference between the jsp scriptlet tag and jsp declaration tag?

Ans. The jsp scriptlet tag can only declare variables not methods whereas jsp declaration tag can declare variables as well as methods.

The declaration of scriptlet tag is placed inside the _jspService() method whereas The declaration of jsp declaration tag is placed outside the _jspService() method.

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Q23. Difference between GET and POST Requests ?

Ans. GET is supposed to get information from the server. Client sends the minimal information so that Server can respond with the response body on basis of request. For example - You want to get complete employment record for employee id 123

POST is supposed to send the information for submission. Payload or a Body is usually sent so that it can be persisted on the server. For example - Sending the complete information of an employee ( id, name , dept etc ) to the server for persisting it.

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Usually asked to entry level software developers.

Q24. Write a program to swap two variables without using third

Ans. public static void main(String[] args) {
   int num1 = 1;
   int num2 = 2;
   num1 = num1^num2;
   num2 = num1^num2;
   num1 = num1^num2;
   System.out.print("num1 = " + num1 +", num2 = "+num2);
}

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Q25. What is the difference between single instance Web environment and Load Balanced Auto Scaling ?

Amazon Web Services (AWS)

Ans. Single instance means there is only 1 instance that will bear all the traffic load whereas Load balanced server means that there will be a cluster of servers that will host the application and load will be balanced distributed among them. Auto Scaling means that the number of instances will be expanded / shrunken based on the rule. Rule could be the traffic count , response time etc.

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Q26. What is cloud computing ?

Cloud Computing

Ans. Cloud Computing is a way of using IT infrastructure with following traits -

1. On Demand Infrastructure
2. Broad Network Access
3. Resource Pooling
4. Rapid Elasticity
5. Measured Service

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Q27. What are the services provided by AWS ?

Amazon Web Services (AWS)

Ans. AWS provides various types of services like Computing ( EC2 , Lambda , EKS ), Storage ( S3, Glacier ), Database ( RDS , DynamoDB ), Streaming ( Kinesis ), Queue ( SQS ), Security and Access ( IAM ) etc.

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Q28. What are the problems one could face while working with serverless technologies like AWS Lambda ?

Amazon Web Services (AWS)

Ans. Warm up time for certain technologies like Java ( JVM Warmup )

Performance

Size of Deployable ( Bigger size packaging should go in S3 )

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Q29. What is the cost of using Cloud Formation ?

Amazon Web Services (AWS)

Ans. Cloud Formation does not have any additional cost but you are charged for the underlying resources it builds.

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Q30. How does AWS Lambda handle failure during event processing?

Amazon Web Services (AWS)

Ans. In AWS Lambda we can run a function in synchronous or asynchronous mode. In synchronous mode, if AWS Lambda function fails, then it will just give an exception to the calling application. In asynchronous mode, if AWS Lambda function fails then it will retry the same function at least 3 times.If AWS Lambda is running in response to an event in Amazon DynamoDB or Amazon Kinesis, then the event will be retried till the Lambda function succeeds or the data expires. In DynamoDB or Kinesis, AWS maintains data for at least 24 hours.

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Q31. What does AMI include ?

Amazon Web Services (AWS)

Ans. A template for the instance.

Launch permission decisions

A block device mapping, when an instance is launched it determines the volumes to attach to that instances.

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Q32. Why is cloud infrastructure so powerful ?

Cloud Computing

Ans. Because it gives the ability to provision infrastructure on Demand with No contracts and strings attached.

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Q33. Which region is the latest and most popular in AWS ? What are the advantages and disadvantages of using this region ?

Amazon Web Services (AWS)

Ans. US-East Virginia

This is the oldest and most popular region. All new features are rolled first in this region and hence they are first available there. The downside is that because of experimentation with new services, unavailability time is quite high.

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Q34. What are the advantage of having Edge Locations ?

Amazon Web Services (AWS)

Ans. It saves Network traffic and facilitates faster delivery by hosting bulk media and cached data near to client.

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Q35. What does effect , action and resource means with respect to AWS IAM policy ?

Amazon Web Services (AWS)

Ans. effect means whether the effect of this Policy is to allow or deny, action means the type of action ( read , write ) and service, and resource is the resource where this should apply.

For example - If we want to have a Policy of providing read access on S3 ,
effect will be "allow"
action will be "s3:GetObject"
resource will be "arn:aws:s3:::examplebucket/*"

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Q36. Within AWS S3, Why new files are available immediately for read operation but not the updates ?

Amazon Web Services (AWS)

Ans. Because new files will be fed from where ever they are first available but AWS have no way to identify which is the most updated version among the various regions. The updated version can only be assured once the replication to all availability zones is complete.

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Q37. What kind of Access Policy should be kept on S3 Buckets and Policy ?

Amazon Web Services (AWS)

Ans. We should only allow access that's needed. So the security Policy should be as restrictive as possible.

Buckets and Files should never be made public unless until they are needed it to be like that.

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Q38. How can we protect from accidental deletes in S3 ?

Amazon Web Services (AWS)

Ans. Versioning ( will create Delete marker )
MFA Delete ( authentication upon deletion )
Cross Region Replication ( Replicates aren't deleted )

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Q39. How can we restrict CloudFront access to a particular Geography ?

Amazon Web Services (AWS)

Ans. We can select the appropriate Price Class if that suits us.

We can do Geo Targeting by black listing / white listing certain geographies.

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Q40. What is the use case for "On Demand" EC2 ?

Amazon Web Services (AWS)

Ans. If the computation required is Spiky and unpredictable.

If it's first time use.

If the lifespan of the application isn't known.

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