[BREAKING Change] Single ServiceMonitor for store shards

[craigfurman]

• I added CHANGELOG entry for this change.
• Change is not relevant to the end user.

Changes

The Prometheus operator creates 1 job per endpoint on each
ServiceMonitor object it discovers. When using the thanos-store hashmod
sharding feature of kube-thanos, 1 ServiceMonitor was created per store
shard. This resulted in 1 prometheus job per shard, with names like
"thanos-store-0", "thanos-store-1".

This commit changes this behavior to instead create only 1
ServiceMonitor, with a Service label selector that selects all Services
for the shards.

Verification

make generate validate, and I've experimented with it in a consumer repository that I use to manage thanos.

[SuperQ]

Ping @kakkoyun @metalmatze :-)

[kakkoyun]

Looking good. I like the idea of having a single service monitor. However, can we avoid nesting?

[kakkoyun]

🥇

[craigfurman]

Thanks @kakkoyun! I'm not sure how we're supposed to communicate breaking changes like this, if at all? I guess users will see their kubectl diffs (or similar) change when they jb update this lib?

[kakkoyun]

Thanks @kakkoyun! I'm not sure how we're supposed to communicate breaking changes like this, if at all? I guess users will see their kubectl diffs (or similar) change when they jb update this lib?

@craigfurman More or less that is what's going to happen. We have a changelog and what we can this change as breaking change. And we can mention it in our release (the exact same process that we have in Thanos).

Thanks for reminding this. I can create another PR to mark this change as a breaking one. Or do you want to do that?

[kakkoyun]

For example https://github.com/thanos-io/thanos/blob/master/CHANGELOG.md

NOTE: As semantic versioning states all 0.y.z releases can contain breaking changes in API (flags, grpc API, any backward compatibility)

We use breaking ⚠️ to mark changes that are not backwards compatible (relates only to v0.y.z releases.)

We already have that mentioned in our changelog as well: https://github.com/thanos-io/kube-thanos/blob/master/CHANGELOG.md

[craigfurman]

@kakkoyun oops, I didn't see that message in the changelog 😅

wdyt of #189?