Decoupling Mechanisms Using AWS Services

1. What is the disadvantage of enabling sticky sessions?
A sticky session has the advantage of ensuring that the end user who establishes a session with an application server can continue to communicate with that application server for the life of the session. However, the disadvantage is that if the application server fails, the user is sent to another application server, which will know nothing about the previous session. This might not be a huge issue if the user is merely reading reports as he or she could simply start again. However, a user in the midst of purchasing a product would have to start over.

2. What is the advantage of using a central location to store user state information?
The advantage of using a central location to store user state information is that the storage location is redundant, and it operates in memory and therefore is fast. However, the main advantage of using a centralized storage location is that the user state information is stored in an independent location and not at the user location or at the server location, which provides a higher level of redundancy and availability.

3. What is the purpose of enabling notifications with Simple Notification Service?
Because every AWS service allows you to link issues with the associated service directly with the notification service (SNS), you have the ability of responding to issues at any time, either with manual steps or through automated solution steps.

4. How can Simple Notification Service and Simple Queue Service work together?
SQS can be a client of SNS. The notification service can send messages to specific queues, which have, in turn, application servers as clients. Therefore, an upload of the file to an S3 bucket could prompt a notification, which could be passed on to a queue, which could be processed by the associated application servers automatically.

5. Where is the advantage in using Step Functions?
Step Functions allows you to craft workflows using SQS and SNS and a variety of AWS services, through a GUI interface. Step Functions has a logical component that can interface with the stateless services of a workflow.

6. What is the advantage of using Lambda to respond to SNS notifications?
Utilizing Lambda to respond to notifications allows you to craft automated responses to any notifications that are generated.

7. Why would you use Lambda to create serverless applications?
Using Lambda to create a serverless application allows you to focus on creating functions that map to the tasks in the application. For example, say that you need an application that has five functions: Login, Search, Save, Download, and Logout. Using Lambda, you could create five separate functions and load those functions into Lambda. Then you could generate an application on your mobile device to call those functions as required. Each function would carry out its specific task when called. You are then charged only when the functions are called.

8. How can Lambda be used with API Gateway?
Lambda can be used with API Gateway much as it is used with a notification service. An API call can communicate with a Lambda function and carry out a task, as required, by using an AWS service.