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4_SoftTopologyAndDuplicates_RemoveDuplicates.md

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Descheduler Profile - SoftTopologyAndDuplicates - RemoveDuplicates Strategy

Before proceeding, the Descheduler Operator must be installed.

WARNING Do not run this in a LIVE cluster, this should be dedicated to the specific tests, as it will EVICT running pods every 1 minute when the Pods are older than 5m. WARNING

RemoveDuplicates: This strategy makes sure that there is only one pod associated with a ReplicaSet (RS), ReplicationController (RC), StatefulSet, or Job running on the same node. If there are more, those duplicate pods are evicted for better spreading of pods in a cluster. This issue could happen if some nodes went down due to whatever reasons, and pods on them were moved to other nodes leading to more than one pod associated with a RS or RC, for example, running on the same node. Once the failed nodes are ready again, this strategy could be enabled to evict those duplicate pods.

Steps

  1. Update the SoftTopologyAndDuplicates Policy
$ oc apply -n openshift-kube-descheduler-operator -f files/4_SoftTopologyAndDuplicates_RemoveDuplicates.yml
kubedescheduler.operator.openshift.io/cluster created
  1. Check the configmap to see the Descheduler Policy.
$ oc -n openshift-kube-descheduler-operator get cm cluster -o=yaml

This ConfigMap should show the excluded namespaces and strategies.RemoveDuplicates is configured and includeSoftConstraints: false

  1. Check the descheduler cluster
$ oc -n openshift-kube-descheduler-operator logs -l app=descheduler

This log should show a started Descheduler.

  1. Create a test namespace
$ oc get namespace test || oc create namespace test
namespace/test created
  1. Cordon one of the workers so we unbalance the number of assigned pods.

a. List the nodes

$ oc get nodes

b. Select a worker node, such as worker-1.rdr-rhop.sslip.io

c. Cordon the node

$ oc adm cordon worker-1.rdr-rhop.sslip.io
node/worker-1.rdr-rhop.sslip.io cordoned
  1. Create a ReplicaSet
$ oc -n test apply -f files/4_SoftTopologyAndDuplicates_rs.yml
replicaset.apps/ua created
  1. Check the pods are all on the other node
$ oc -n test get pods -o=custom-columns='Name:metadata.name,NodeName:spec.nodeName' -lapp=ua
Name                          NodeName
ua-54pmt   worker-0.rdr-rhop.sslip.io
ua-8mfx8   worker-0.rdr-rhop.sslip.io
  1. Uncordon the worker.
$ oc adm uncordon worker-1.rdr-rhop.sslip.io              
node/worker-1.rdr-rhop.sslip.io uncordoned
  1. Check the Logs until we see the processing
$ oc -n openshift-kube-descheduler-operator logs -l app=descheduler  --tail=200                                 
I0512 19:35:45.106891       1 duplicates.go:199] "Adjusting feasible nodes" owner={namespace:test kind:ReplicaSet name:unbalanced-6d757874c4 imagesHash:docker.io/ibmcom/pause-ppc64le:3.1} from=5 to=2
I0512 19:35:45.106915       1 duplicates.go:207] "Average occurrence per node" node="worker-1.rdr-rhop.sslip.io" ownerKey={namespace:test kind:ReplicaSet name:ua-8mfx8 imagesHash:docker.io/ibmcom/pause-ppc64le:3.1} avg=1
I0512 19:35:45.126413       1 evictions.go:160] "Evicted pod" pod="test/ua-8mfx8" reason="RemoveDuplicatePods"
I0512 19:35:45.126547       1 descheduler.go:287] "Number of evicted pods" totalEvicted=1
  1. Check the pods are now redistributed.
$ oc -n test get pods -o=custom-columns='Name:metadata.name,NodeName:spec.nodeName' -lapp=ua
Name                          NodeName
ua-54pmt   worker-1.rdr-rhop.sslip.io
ua-8mfx8   worker-0.rdr-rhop.sslip.io
  1. Delete the deployment
oc -n test delete replicaset.apps/ua
replicaset.apps "ua" deleted

Summary

This Profile shows the SoftTopologyAndDuplicates and how it causes descheduling and scheduling, it's basically a duplicate of TopologyAndDuplicates.