Dynamic topology

In the previous section, you used and tested the Liqo namespace offloading mechanism and how it can prevent from an undesired scheduling. In this section, you will get in touch with how Liqo deals with dynamic topologies. More precisely, given a cluster-selector in a NamespaceOffloading, Liqo adds peered newcomers clusters to the schedulable set. Complementarily, Liqo will force the rescheduling of workloads of clusters that leave the topology. In a nutshell, as a system admin or devops, you do not have to care if new clusters are peered or unpeered at runtime, Liqo ensures the convergence of the toto the new set-up automatically.

In this step, you will try to disable the peering with a cluster that has at least one pod inside. This will show you that a new replacing pod is correctly rescheduled inside another available cluster.

Disable a peering

First, you have to check on which remote clusters your pods have been scheduled:

kubectl get pods -n liqo-test -o wide
NAME                               READY   STATUS    RESTARTS   IP            NODE                                        
nginx-deployment-5c97c84f6-5p47g   1/1     Running   0   liqo-b07938e3-d241-460c-a77b-e286c0f733c7   
nginx-deployment-5c97c84f6-8h58s   1/1     Running   0   liqo-b38f5c32-a877-4f82-8bde-2fd0c5c8f862   
nginx-deployment-5c97c84f6-cf8qc   1/1     Running   0   liqo-b07938e3-d241-460c-a77b-e286c0f733c7   

Given that, in this case, 2 pods are scheduled in cluster-3, we can disable the peering with that cluster to test what happens to our pods and services when we dynamically change the topology.

If all your pods have been scheduled in cluster-2, you have to disable that peering using the env variable $REMOTE_CLUSTER_ID_2 instead of $REMOTE_CLUSTER_ID_3.

You can now disable the peering with the cluster-3.

kubectl patch foreignclusters $REMOTE_CLUSTER_ID_3 \
--patch '{"spec":{"outgoingPeeringEnabled":"No"}}' \
--type 'merge'

The remote namespace in the cluster-3 is teared down. After a couple of seconds, you should see all the three pods scheduled in the remaining cluster (cluster-2 in this example):

kubectl get pods -n liqo-test 

The output will be something like:

NAME                                     READY   STATUS    
nginx-deployment-5c97c84f6-8h58s-58w27   1/1     Running   
nginx-deployment-5c97c84f6-hvfb9-6tqll   1/1     Running   
nginx-deployment-5c97c84f6-rb4rz-4b5qd   1/1     Running

Resume the peering

You can now try to resume the previous peering:

kubectl patch foreignclusters $REMOTE_CLUSTER_ID_3 \
--patch '{"spec":{"outgoingPeeringEnabled":"Yes"}}' \
--type 'merge'

The namespaces created on the newly peered cluster is immediately updated and cluster-3 is re-added to the multi-cluster topology. A remote namespace is correctly re-created in cluster-3:

kubectl get namespace liqo-test 
liqo-test   Active   40s

Clean up the environment

To clean up your environment, you have to execute the following steps:

  1. Delete the deployed pods and the service:

    kubectl delete deployment nginx-deployment -n liqo-test
  2. Delete the namespaceOffloading resource and the associated Liqo namespace:

    kubectl delete namespaceoffloading offloading -n liqo-test
    kubectl delete namespace liqo-test
  3. Disable the two (unidirectional) peerings to get ready to uninstall Liqo:

    kubectl patch foreignclusters $REMOTE_CLUSTER_ID_2 \
    --patch '{"spec":{"outgoingPeeringEnabled":"No"}}' \
    --type 'merge'
    kubectl patch foreignclusters $REMOTE_CLUSTER_ID_3 \
    --patch '{"spec":{"outgoingPeeringEnabled":"No"}}' \
    --type 'merge'