Adds probes, but for Kafka I don't think it indicates readiness...

which might not matter because we no longer have a loadbalancing service.

These probes won't catch all failure modes,
but if they fail we're pretty sure the container is malfunctioning.

I found some sources recommending ./bin/kafka-topics.sh for probes
but to me it looks risky to introduce a dependency to some other service for such things.
One such source is helm/charts#144

The zookeeper probe is from
https://kubernetes.io/docs/tasks/configure-pod-container/configure-liveness-readiness-probes/
An issue is that zookeeper's logs are quite verbose for every probe.

50kafka.yml

@@ -47,6 +47,12 @@ spec:
           requests:
             cpu: 100m
             memory: 512Mi
+        livenessProbe:
+          exec:
+            command:
+            - /bin/sh
+            - -c
+            - 'echo "" | nc -w 1 127.0.0.1 9092'
         volumeMounts:
         - name: data
           mountPath: /var/lib/kafka/data

zookeeper/50pzoo.yml

@@ -60,6 +60,18 @@ spec:
           requests:
             cpu: 10m
             memory: 100Mi
+        livenessProbe:
+          exec:
+            command:
+            - /bin/sh
+            - -c
+            - '[ "imok" == $(echo "ruok" | nc -w 1 127.0.0.1 2181) ]'
+        readinessProbe:
+          exec:
+            command:
+            - /bin/sh
+            - -c
+            - '[ "imok" == $(echo "ruok" | nc -w 1 127.0.0.1 2181) ]'
         volumeMounts:
         - name: config
           mountPath: /usr/local/kafka/config

zookeeper/51zoo.yml

@@ -60,6 +60,18 @@ spec:
           requests:
             cpu: 10m
             memory: 100Mi
+        livenessProbe:
+          exec:
+            command:
+            - /bin/sh
+            - -c
+            - '[ "imok" == $(echo "ruok" | nc -w 1 127.0.0.1 2181) ]'
+        readinessProbe:
+          exec:
+            command:
+            - /bin/sh
+            - -c
+            - '[ "imok" == $(echo "ruok" | nc -w 1 127.0.0.1 2181) ]'
         volumeMounts:
         - name: config
           mountPath: /usr/local/kafka/config