17 September 2023

JSF applications rely on sticky sessions. This means, the server-side JVM maintains state (usally in memory) for a particular user/client. For this, each request needs to be routed to the same JVM; in Kubernetes language: to the same pod. The relation between client and server is achieved by sending a session-cookie to the browser. The browser sends this cookie to the server in every request. Now the infrastructure in between needs to be set up so it recognizes this cookie (it needs to be aware about this cookie / the name of the cookie) and routes / pins the request appropriately to the same pod.

I wanted to see how exactly this needs to be set up in the context of AWS Elastic Kubernetes Service (EKS). For that I created this Github repository. It uses AWS' Java CDK to deploy the infrastructure (Elastic Container Registry, Elastic Kubernetes Service) and then deploys a simple Quarkus application that helped me verify the correct handling of the cookie / the stickyness.

The only step to run is ./deploy.sh all. This will provision the AWS infrastructure and then deploy the application assuming you have used AWS on your system before and have valid AWS credentials configured.

Running kubectl get pods -o wide you should see that because we have provisioned two EC2 nodes as part of the Kubernetes cluster that the pods are running on different nodes.

The output of the deploy.sh should have given you the public endpoint that was provisioned (Access @ http://<aws-public-endpoint>/hello should have been printed). Accessing this endpoing will print all environment variables of the pod. If you run http://<aws-public-endpoint>/hello?var=HOSTNAME it will print only the hostname of the pod. You should see that on each request you get a different pod due to the load balancer. If you access http://<aws-public-endpoint>/hello/session instead, you should see that it should connect to the same pod each time because a cookie gets used. The cookie name that is created in the code (https://github.com/38leinaD/aws-playground/blob/master/app/src/main/java/de/dplatz/TestResource.java#L29) needs to match the configuration of the Application Loadbalancer (ALB) in the ingress configuration (https://github.com/38leinaD/aws-playground/blob/master/deployment/k8s/services.yaml#L65; see stickiness.app_cookie.cookie_name=mycookie).

Please note that for the ingress to work properly, the ALB controller needs to be configured as part of provisioning the EKS cluster:

Cluster eksCluster = Cluster.Builder.create(this,"eks-cluster")
        .defaultCapacityInstance(InstanceType.of(InstanceClass.T3, InstanceSize.SMALL))
        .albController(AlbControllerOptions.builder() (1)
  1. ALB controller required by the ingress

See here for the full CDK stack.

Don’t forget to run ./deploy.sh destroy at the end to shut everything down again.