Feature Request: Allow and replace macros in annotations

[joewreschnig]

In some cases my services need to connect to specific shards to modify/retrieve data. I usually control externally-visible names via the external-dns.alpha.kubernetes.io/hostname annotation; I'd like to be able to do the same here using the shard and replica template macros within the annotation to expose e.g. each replica under a unique name:

      - name: replica
        generateName: db-{clusterID}-{shard}-{replica}
        metadata:
          annotations:
            external-dns.alpha.kubernetes.io/hostname: clickhouse-{clusterID}-{shard}-{replica}.example.com
        spec:
          type: LoadBalancer
          ....

But this currently results in the annotation clickhouse-{clusterID}-{shard}-{replica}.example.com.

If this needs to be done under e.g. a new generateAnnotations option for backwards-compatibility, that's also fine with me, as long as I have some way to attach them.

[alex-zaitsev]

@joewreschnig , have you looked into serviceTemplates?

clickhouse-operator/docs/chi-examples/99-clickhouseinstallation-max.yaml

Line 212 in e62c7c8

serviceTemplates:

Some examples:
https://github.com/Altinity/clickhouse-operator/blob/master/tests/configs/test-012-service-template.yaml

[joewreschnig]

Yes, the above is the relevant part of my service template. As far as I can see the template replacement applies only to the generateName and not any of the annotations or other fields.

[alex-zaitsev]

That's right, make sense. In Altinity.Cloud we use annotations in order to configure external load balancer and moved templating logic on that level. But it makes sense to add it to an operator as well. Will take it as a feature request to 0.17.0

[alex-zaitsev]

Implemented in 0.17.0 version
cc @joewreschnig