Tips & Tricks for running Strimzi with kubectl

When running Apache Kafka on Kubernetes with Strimzi, one of the tools you might use very often is kubectl. You can use it for controlling your Kubernetes cluster and its resources. Because Strimzi is using custom resources to extend the Kubernetes APIs, you can also use kubectl with Strimzi. In this blog post, we will have a look at some tips and tricks on how to make using kubectl with Strimzi easier.

Working with Kubernetes resources

kubectl can be used for all basic tasks with the Strimzi custom resources. You can use all kubectl commands such as get, describe, edit, or delete coupled with the resource type. So for example kubectl get kafkatopics will get you a list of all Kafka topics or kubectl get kafkas to get all Kafka clusters.

When referencing a resource types, you can use both singular and plural. So kubectl get kafkas gets you the same results as kubectl get kafka. But a lesser known feature is that you can reference custom resources with their short name. The short name for Kafka is k, so you can for example also run kubectl get k to list all your deployed Kafkas.

$ kubectl get k
NAME         DESIRED KAFKA REPLICAS   DESIRED ZK REPLICAS
my-cluster   3                        3

The following table shows all our resources and their short names:

This is really handy because some of the resources have longer names. So learning the short names can save a lot of time while operating Strimzi or working on new features.

Resource categories

The custom resources can be also grouped into categories. The name of the category can be used in the kubectl commands instead of the individual resource types. All Strimzi custom resources are in the category strimzi, so you can use it to get all the Strimzi resources with one command. For example running kubectl get strimzi will lists all the different Strimzi custom resources which exist in given namespace. The output will look something like the following:

$ kubectl get strimzi
NAME                                DESIRED KAFKA REPLICAS   DESIRED ZK REPLICAS
kafka.kafka.strimzi.io/my-cluster   3                        3

NAME                                          PARTITIONS   REPLICATION FACTOR
kafkatopic.kafka.strimzi.io/kafka-test-apps   3            3

NAME                                 AUTHENTICATION   AUTHORIZATION
kafkauser.kafka.strimzi.io/my-user   tls              simple

You can also combine this with other commands. For example while developing or testing new Strimzi features, I quite often need to delete all Strimzi custom resources. Doing it resource by resource would take a long time. But I can delete them all in a single command:

$ kubectl delete $(kubectl get strimzi -o name)
kafka.kafka.strimzi.io "my-cluster" deleted
kafkatopic.kafka.strimzi.io "kafka-test-apps" deleted
kafkauser.kafka.strimzi.io "my-user" deleted

The inner command - kubectl get strimzi -o name - will return the types and the resource names. This is enabled by the -o name option.

$ kubectl get strimzi -o name
kafka.kafka.strimzi.io/my-cluster
kafkatopic.kafka.strimzi.io/kafka-test-apps
kafkauser.kafka.strimzi.io/my-user

And when this is passed into the kubectl delete command, it will delete all Strimzi resources.

Querying the status subresources

We already saw how the -o name option can be used to get the output in the type/name format. There are also other values you can pass to the -o option. For example by using -o yaml you can get the output in YAML format. Or -o json will return it as JSON. You can see all the options in kubectl get --help or in the kubectl docs.

One of the most useful options is jsonpath. It allows you to pass JSONPath expression which will be evaluated while querying the Kubernetes API. The JSONPath expression can be used to extract or navigate specific parts of any resource. For example, you can get the bootstrap address from the status of the Kafka custom resource and use it in your Kafka clients. You can do that with the following JSONPath expression - {.status.listeners[?(@.type=="tls")].bootstrapServers}:

$ kubectl get kafka my-cluster -o=jsonpath='{.status.listeners[?(@.type=="tls")].bootstrapServers}{"\n"}'
my-cluster-kafka-bootstrap.myproject.svc:9093

The command above will find the bootstrapServers value of the tls listeners. By changing the type condition to @.type=="external" or @.type=="plain" you can also get the address of the other Kafka listeners.

$ kubectl get kafka my-cluster -o=jsonpath='{.status.listeners[?(@.type=="external")].bootstrapServers}{"\n"}'
192.168.1.247:9094

You can similarly extract any other field or group of fields from any custom resource.

Conclusion

kubectl on first appearance looks like a simple tool, but it has also some very powerful features, useful for everyday development. I hope this blog post will help you to be more efficient when managing Strimzi with the kubectl tool.