# Kafka on Kubernetes (Strimzi) Single-broker Kafka cluster for dev/test, deployed via the [Strimzi](https://strimzi.io/) operator on a single-node k3s cluster. --- ## Architecture ``` kafka namespace ├── strimzi-cluster-operator Strimzi operator — reconciles Kafka/KafkaUser/KafkaTopic CRs ├── kafka-dual-role-0 Kafka 4.1.0 broker (KRaft, controller + broker in one pod) └── kafka-entity-operator Topic Operator + User Operator (manages topics and users) ``` ### Key design decisions | Choice | Rationale | |---|---| | **KRaft mode** | No ZooKeeper dependency — simpler, fewer pods | | **Single node pool** `dual-role` | One pod acts as both controller and broker, suitable for dev/test | | **SASL_SSL + SCRAM-SHA-512** | Authenticated and encrypted connections; TLS managed by Strimzi CA | | **Simple authorization** | ACLs enforced per user; `kafka-admin` is declared super user | | **`local-path` storage (10 Gi)** | Default k3s storage class; PVC deleted on cluster teardown | ### Listeners | Name | Port | Protocol | Auth | |---|---|---|---| | `tls` | 9093 | SASL_SSL | SCRAM-SHA-512 | Bootstrap address (cluster-internal): ``` kafka-kafka-bootstrap.kafka.svc.cluster.local:9093 ``` ### Users | KafkaUser | Secret | Role | |---|---|---| | `kafka-admin` | `kafka-admin` | Super user — unrestricted access | | `kafka-client` | `kafka-client` | Application user — Read/Write all topics and groups | Strimzi stores credentials in Kubernetes secrets. Each secret contains two keys: - `password` — the SCRAM password - `sasl.jaas.config` — the ready-to-use JAAS config string ### TLS Strimzi generates and manages its own internal CA. The cluster CA certificate is stored in: ``` secret/kafka-cluster-ca-cert (key: ca.crt) ``` This certificate must be trusted by any Kafka client connecting over TLS. --- ## Prerequisites - `kubectl` configured against the target cluster - `helm` v3 - `cert-manager` is **not** required — Strimzi manages its own CA --- ## Installation ```bash ./deploy.sh ``` The script performs the following steps: 1. Creates the `kafka` namespace 2. Installs the Strimzi operator via Helm (scoped to the `kafka` namespace) 3. Waits for the Strimzi CRDs to be fully established 4. Applies `kafka.yaml` (KafkaNodePool + Kafka CRs) and waits for `Ready` 5. Applies `kafka-users.yaml` (KafkaUser CRs) and waits for `Ready` Expected duration: **4–6 minutes** on a single-node k3s cluster. ### Verify the installation ```bash kubectl get kafka,kafkanodepool,kafkauser,pods -n kafka ``` Expected output: ``` NAME READY KAFKA VERSION METADATA VERSION kafka.kafka.strimzi.io/kafka True 4.1.0 4.1-IV0 NAME DESIRED REPLICAS ROLES NODEIDS kafkanodepool.kafka.strimzi.io/dual-role 1 ["controller","broker"] [0] NAME CLUSTER AUTHENTICATION AUTHORIZATION READY kafkauser.kafka.strimzi.io/kafka-admin kafka scram-sha-512 True kafkauser.kafka.strimzi.io/kafka-client kafka scram-sha-512 simple True ``` --- ## Client configuration ### Get the CA certificate ```bash kubectl -n kafka get secret kafka-cluster-ca-cert \ -o jsonpath='{.data.ca\.crt}' | base64 -d > kafka-ca.crt ``` ### Get user credentials ```bash # Admin password kubectl -n kafka get secret kafka-admin \ -o jsonpath='{.data.password}' | base64 -d # Client password kubectl -n kafka get secret kafka-client \ -o jsonpath='{.data.password}' | base64 -d # Ready-to-use JAAS config (includes username and password) kubectl -n kafka get secret kafka-client \ -o jsonpath='{.data.sasl\.jaas\.config}' | base64 -d ``` ### Sample `client.properties` ```properties bootstrap.servers=kafka-kafka-bootstrap.kafka.svc.cluster.local:9093 security.protocol=SASL_SSL ssl.truststore.type=PEM ssl.truststore.location=/path/to/kafka-ca.crt sasl.mechanism=SCRAM-SHA-512 sasl.jaas.config=org.apache.kafka.common.security.scram.ScramLoginModule required \ username="kafka-client" password=""; ``` --- ## Testing A smoke test job is provided that validates the full produce/consume cycle over SASL_SSL. ### Run the smoke test ```bash kubectl apply -f kafka-smoke-test.yaml kubectl logs -n kafka -l job-name=kafka-smoke-test -f ``` ### Re-run ```bash kubectl delete job kafka-smoke-test -n kafka kubectl apply -f kafka-smoke-test.yaml kubectl logs -n kafka -l job-name=kafka-smoke-test -f ``` ### What the test does 1. **Topic creation** — creates topic `smoke-test` with `--if-not-exists` (idempotent) 2. **Produce** — sends 5 messages (`message-1` … `message-5`) via `kafka-console-producer` 3. **Consume** — reads 5 messages from the beginning via `kafka-console-consumer` and asserts count Expected output: ``` ==> [1/3] Creating topic 'smoke-test' (idempotent) Topic ready. ==> [2/3] Producing 5 messages 5 messages produced. ==> [3/3] Consuming (from-beginning, max 5) message-1 message-2 message-3 message-4 message-5 ==> SMOKE TEST PASSED (5/5 messages) ``` The job is cleaned up automatically after 10 minutes (`ttlSecondsAfterFinished: 600`). --- ## Adding a new user Create a new `KafkaUser` manifest following the `kafka-client` pattern in `kafka-users.yaml`, then apply it: ```bash kubectl apply -f kafka-users.yaml ``` Strimzi will create the corresponding secret in the `kafka` namespace within seconds. --- ## Upgrade ### Upgrade the Kafka version Supported versions are dictated by the installed Strimzi operator. Check available versions: ```bash kubectl get kafka kafka -n kafka \ -o jsonpath='{.status.kafkaVersion}' helm show chart strimzi/strimzi-kafka-operator | grep appVersion ``` To upgrade Kafka from e.g. `4.1.0` to `4.1.1`: 1. Update `spec.kafka.version` in `kafka.yaml` 2. Update `spec.kafka.metadataVersion` if the new version introduces a new metadata version 3. Apply the change: ```bash kubectl apply -f kafka.yaml kubectl wait kafka/kafka --for=condition=Ready --timeout=10m -n kafka ``` Strimzi performs a rolling restart of the broker pod automatically. ### Upgrade the Strimzi operator ```bash helm repo update strimzi helm upgrade strimzi-kafka-operator strimzi/strimzi-kafka-operator \ --namespace kafka \ --set watchAnyNamespace=false \ --wait --timeout 5m ``` > **Note:** always upgrade the operator before upgrading the Kafka version. Check the [Strimzi upgrade guide](https://strimzi.io/docs/operators/latest/deploying.html#assembly-upgrade-str) for supported upgrade paths. --- ## Uninstallation ```bash # Delete Kafka cluster and users (PVC is deleted because deleteClaim: true) kubectl delete -f kafka-users.yaml kubectl delete -f kafka.yaml # Wait for pods to terminate kubectl wait --for=delete pod -l strimzi.io/cluster=kafka -n kafka --timeout=120s # Uninstall Strimzi operator helm uninstall strimzi-kafka-operator -n kafka # Delete namespace (removes all remaining secrets and CRDs bindings) kubectl delete namespace kafka ``` > The `deleteClaim: true` flag in `kafka.yaml` ensures the 10 Gi PVC is deleted together with the KafkaNodePool, leaving no orphaned volumes.