// This assembly is included in the following assemblies:
//
// using/assembly-management-tasks.adoc

[id='assembly-drain-cleaner-{context}']
= Evicting pods with Strimzi Drain Cleaner

[role="_abstract"]
Kafka and ZooKeeper pods might be evicted during Kubernetes upgrades, maintenance or pod rescheduling.
If your Kafka broker and ZooKeeper pods were deployed by Strimzi, you can use the Strimzi Drain Cleaner tool to handle the pod evictions.
Since the Strimzi Drain Cleaner will handle the eviction instead of Kubernetes, you need to set the `podDisruptionBudget` for your Kafka deployment to `0` (zero).
Kubernetes will then no longer be allowed to evict the pod automatically.

By deploying the Strimzi Drain Cleaner, you can use the Cluster Operator to move Kafka pods instead of Kubernetes.
The Cluster Operator ensures that topics are never under-replicated.
Kafka can remain operational during the eviction process.
The Cluster Operator waits for topics to synchronize, as the Kubernetes worker nodes drain consecutively.

An admission webhook notifies the Strimzi Drain Cleaner of pod eviction requests to the Kubernetes API.
The Strimzi Drain Cleaner then adds a rolling update annotation to the pods to be drained.
This informs the Cluster Operator to perform a rolling update of an evicted pod.

NOTE: If you are not using the Strimzi Drain Cleaner, you can xref:proc-manual-rolling-update-pods-str[add pod annotations to perform rolling updates manually].

.Webhook configuration
The Strimzi Drain Cleaner deployment files include a `ValidatingWebhookConfiguration` resource file.
The resource provides the configuration for registering the webhook with the Kubernetes API.

The configuration defines the `rules` for the Kubernetes API to follow in the event of a pod eviction request.
The rules specify that only `CREATE` operations related to `pods/eviction` sub-resources are intercepted.
If these rules are met, the API forwards the notification.

The `clientConfig` points to the Strimzi Drain Cleaner service and `/drainer` endpoint that exposes the webhook.
The webhook uses a secure TLS connection, which requires authentication.
The `caBundle` property specifies the certificate chain to validate HTTPS communication.
Certificates are encoded in Base64.

.Webhook configuration for pod eviction notifications
[source,yaml,subs="attributes+"]
----
apiVersion: admissionregistration.k8s.io/v1
kind: ValidatingWebhookConfiguration
# ...
webhooks:
  - name: strimzi-drain-cleaner.strimzi.io
    rules:
      - apiGroups:   [""]
        apiVersions: ["v1"]
        operations:  ["CREATE"]
        resources:   ["pods/eviction"]
        scope:       "Namespaced"
    clientConfig:
      service:
        namespace: "strimzi-drain-cleaner"
        name: "strimzi-drain-cleaner"
        path: /drainer
        port: 443
        caBundle: Cg==
    # ...
----

[id='drain-cleaner-prereqs-{context}']
== Prerequisites

To deploy and use the Strimzi Drain Cleaner, you need to download the deployment files.

The Strimzi Drain Cleaner deployment files are available from the link:{ReleaseDownload}.

//steps for deploying drain cleaner
include::modules/proc-drain-cleaner-deploying.adoc[leveloffset=+1]
//steps for using drain cleaner
include::modules/proc-drain-cleaner-using.adoc[leveloffset=+1]
