在Elastic Beanstalk中维护会话

Question

As the number of instances changes from time to time in Amazon Elastic Beanstalk. If an application is built in PHP how the session will be maintained among several instances? How can we make sure not to delete the Parent instance (The first instance when the app was start

Answer 1

This post on the AWS blog describes how to use DynamoDB to do session state handling using the AWS SDK for PHP.

http://aws.typepad.com/aws/2012/04/scalable-session-handling-in-php-using-amazon-dynamodb.html

Answer 2

If an application is built in PHP how the session will be maintained among several instances?

No. Elastic Beanstalk will not maintain session among several instances. You must maintain session among several instances by yourself. If you enable Elastic Load Balancing Session Stickiness, it will only make sure to forward your user to the same instance.

How can we make sure not to delete the Parent instance (The first instance when the app was start

Elastic Beanstalk Auto Scaling is use Default Termination Policy which will terminate oldest instance first. You can modify Elastic Beanstalk Auto Scaling Termination Policy to avoid terminating oldest instance first.

Answer 3

From personal experience I would suggest moving sessions to the database (RDS|DynamoDB|SimpleDB) or cache server (AWS started supporting Redis recently). It would take a lot of headache when application starts to scale or get terminated by unsuccesful health check.

Answer 4

Here is a tutorial for how to configure persistent sessions using DynamoDB and Tomcat. https://packageprogrammer.wordpress.com/2014/01/13/aws-elastic-beanstalk-and-dynamodb-session-manager-for-tomcat/

AWS Project: https://github.com/aws/aws-dynamodb-session-tomcat

Manage Tomcat Session State with DynamoDB: http://docs.aws.amazon.com/sdk-for-java/v1/developer-guide/java-dg-tomcat-session-manager.html

Key Excerpt from the links above. Note that you may have change version numbers since the tutorial uses Tomcat 7 and 1.0.1 of aws-dynamodb-session-tomcat

Configuration for Tomcat

Download AmazonDynamoDBSessionManagerForTomcat-2.0.4.jar from aws-dynamodb-session-tomcat releases the and copy to the lib directory of your Tomcat installation Edit context.xml to use the .jar with code:

<?xml version='1.0' encoding='utf-8'?>
<Context>
    <WatchedResource>WEB-INF/web.xml</WatchedResource>
    <Manager className="com.amazonaws.services.dynamodb.sessionmanager.DynamoDBSessionManager"
             createIfNotExist="true" />
</Context>

Configuration for Elastic Beanstalk

Download AmazonDynamoDBSessionManagerForTomcat-2.0.4.jar from aws-dynamodb-session-tomcat releases the and copy into .ebextensions directory of your WAR Edit context.xml with the code below and copy into .ebextensions directory of your WAR In the .ebextensions directory (Remember it must be inside /WEB-INF directory, /web-app for grails applications), create a .config file to write the command to execute the replacement of context.xml and copy the jar inside Beanstalk instances.

container_commands:
  01-copy-aws-library:
    command: "cp WEB-INF/.ebextensions/AmazonDynamoDBSessionManagerForTomcat-2.0.4.jar.jar /usr/share/tomcat8/lib/"
  02-replace-tomcat-context:
    command: "cp WEB-INF/.ebextensions/context.xml /etc/tomcat8/context.xml"

Now, just upload and deploy the war with the changes. Try login and go into AWS Console->Services->DynamoDB, look for a table with name Tomcat_SessionState and voilà! You have affinity and persistence!

Answer 5

Better option to use Redis on Elastic Cache in order to store session. One t1.micro node available on free tier and maintainable by Amazon, so you can get stable, cheep and fast storage for sessions, shared between nodes in autoscalling environment. How to configure PHP for keeping sessions in Redis I guess you can find in internet.

Option with DynamoDB can be expensive, because you will pay for each call to DynamoDB services, also you need take into account that AWS services exposed by HTTP(S) can throttle requests.

Answer 6

I think the only way to manage this is to store your sessions in DynamoDB or similar. We had the exact same problem when we deployed a java based app on Tomcat in the Elastic Bean Environment. When the load balancer used to scale down instances, any user attached to that instance would automatically log out. Moving sessions to DynamoDB solved this problem for us.

Answer 7

When using Elastic Beanstalk with a typical Java webapp, I think you will definitely want to enable session stickiness. Otherwise each HTTP request from a user's browser could be routed to a different server.

To get around the issue of the user's session being destroyed when the server they are "stuck" to gets shut down you would need to look into Tomcat session replication. This isn't something that Elastic Beanstalk comes with out of the box unfortunately, so in order to setup session replication you would have to create a custom Elastic Beanstalk AMI for your application to use. Also, you would have to use an implementation of Tomcat session replication that does not rely on multicast, since multicast isn't available on AWS, or any other cloud environment that I know of. An example of an implementation that doesn't rely on multicast would be one that uses a database (such as Amazon RDS) or memcached server (such as Amazon Elastic Cache) to make the sessions available across multiple Tomcat instances.

Also note that the Elastic Beanstalk UI only allows you to enable load balancer-generated HTTP cookies. However after Elastic Beanstalk has created the load balancer, you can go into the EC2 console and modify the load balancer's settings to switch it to application-generated HTTP cookies, and then tell it to use the "JSESSIONID" cookie.