Strimzi Drain Cleaner

Strimzi Drain Cleaner is an utility which helps with moving the Kafka pods deployed by Strimzi from Kubernetes nodes which are being drained. It is useful if you want the Strimzi operator to move the pods instead of Kubernetes itself. The advantage of this approach is that the Strimzi operator makes sure that no pods become under-replicated during the node draining. To use it:

Deploy Kafka using Strimzi and configure the PodDisruptionBudgets for Kafka and ZooKeeper to have maxUnavailable set to 0. This will block Kubernetes from moving the pods on their own.

apiVersion: kafka.strimzi.io/v1beta2
kind: Kafka
metadata:
  name: my-cluster
spec:
  kafka:
    replicas: 3
    listeners:
      - name: plain
        port: 9092
        type: internal
        tls: false
      - name: tls
        port: 9093
        type: internal
        tls: true
    config:
      offsets.topic.replication.factor: 3
      transaction.state.log.replication.factor: 3
      transaction.state.log.min.isr: 2
    storage:
      type: jbod
      volumes:
      - id: 0
        type: persistent-claim
        size: 100Gi
        deleteClaim: false
    template:
      podDisruptionBudget:
        maxUnavailable: 0
  zookeeper:
    replicas: 3
    storage:
      type: persistent-claim
      size: 100Gi
      deleteClaim: false
    template:
      podDisruptionBudget:
        maxUnavailable: 0
  entityOperator:
    topicOperator: {}
    userOperator: {}

Deploy the Strimzi Drain Cleaner
Drain the node with some Kafka or ZooKeeper pods using the kubectl drain command

How does it work?

Strimzi Drain Cleaner uses Kubernetes Admission Control features and Validating Web-hooks to find out when something tries to evict the Kafka or ZooKeeper pods. It annotates them with the strimzi.io/manual-rolling-update annotation which will tell Strimzi Cluster Operator that this pod needs to be restarted. Strimzi will roll it in the next reconciliation using its algorithms which make sure the cluster is available. This is supported from Strimzi 0.21.0.

Deployment

If you want to use this only to Kafka and not to ZooKeeper, you can edit the Deployment and remove the --zookeeper option.

On OpenShift

On OpenShift, you can have the certificates needed for the web-hook generated automatically and injected into the pod / web-hook configuration. To install the Drain Cleaner on OpenShift, use the ./install/openshift directory:

kubectl apply -f ./install/openshift

On Kubernetes with CertManager

On Kubernetes, when you use Cert Manager, you can have the certificates needed for the web-hook generated automatically and injected into the pod / web-hook configuration. To install the Drain Cleaner on Kubernetes with installed CertManager, use the ./install/certmanager directory:

kubectl apply -f ./install/certmanager

On Kubernetes without CertManager

On Kubernetes, when you do not use Cert Manager, the certificates needed for the web-hook need to be generated manually. Follow the instructions in ./install/kubernetes directory.

See it in action

You can easily test how it works:

Install Strimzi on your cluster
Deploy Kafka cluster with Pod Disruption Budget configuration having maxUnavailable set to 0 as shown in the example above
Install the Drain Cleaner

Drain one of the Kubernetes nodes with one of the Kafka or ZooKeeper pods

kubectl drain <worker-node> --delete-emptydir-data --ignore-daemonsets --timeout=6000s --force

Watch how it works:
- The kubetl drain command will wait for the Kafka / ZooKeeper to be drained
- The Drain Cleaner log should show how it gets the eviction events
- Strimzi Cluster Operator log should show how it rolls the pods which are being evicted

Build

This project uses Quarkus, the Supersonic Subatomic Java Framework. It can be build directly using Maven. But it also has a simple Make build to make it easier to build the binary and the container image.

Running the application in dev mode

You can run the application in dev mode that enables live coding using:

mvn compile quarkus:dev

Creating a native executable using Maven

If you have GraalVM installed locally, you can create a native executable using:

mvn package -Pnative

Or you can run the native executable build for Linux in a container using:

mvn package -Pnative -Dquarkus.native.container-build=true

This is useful especially when running on other operating systems such as macOS or when you don't have GraalVM installed.

You can then execute your native executable with: ./target/strimzi-drain-cleaner-1.0.0-SNAPSHOT-runner.

Creating a native executable using Make

If you have GraalVM installed locally, you can create a native executable using:

make java_package

Or you can run the native executable build for Linux in a container using:

MVN_ARGS=-Dquarkus.native.container-build=true make java_package

This is useful especially when running on other operating systems such as macOS or when you don't have GraalVM installed.

You can then execute your native executable with: ./target/strimzi-drain-cleaner-1.0.0-SNAPSHOT-runner.

Building a container image manually

After you have the native executable, you can build the container manually:

docker build -f Dockerfile -t my-registry.tld/my-org/strimzi-drain-cleaner:latest .
docker push my-registry.tld/my-org/strimzi-drain-cleaner:latest

Update the container image name to match your own registry / organization etc.

Building a container image using Make

You can also build the image and push it into the registry using Make:

make docker_build docker_push

You can use the following environment variables to configure where will the image be pushed:

DOCKER_REGISTRY defines the registry where it will be pushed. For example docker.io.
DOCKER_ORG defines the organization where it will be pushed. For example my-org.
DOCKER_TAG defines the tag under which will the image be pushed.

Test

Some unit tests are included. You can also test it manually by evicting pods or by posting admission reviews.

Evicting pods

Install the Drain Cleaner
Proxy to the Kubernetes API server
```
kubectl proxy
```

Use curl to trigger eviction (change pod name and namespace as needed):

curl -v -H 'Content-type: application/json' http://localhost:8001/api/v1/namespaces/myproject/pods/my-cluster-zookeeper-1/eviction -d @src/test/resources/example-eviction-request.json

Posting admission review requests

Run Drain Cleaner locally (mvn compile quarkus:dev)

Use curl to post the Admission Review Request manually:

curl -v -H 'Content-type: application/json' http://localhost:8080/drainer -d @src/test/resources/example-admission-review.json

im-konge / drain-cleaner