Loki Tanka microservices: common environment variables

[irizzant]

What this PR does / why we need it:

This PR adds commonEnvs config parameter to specify variables common to all Pod and it was created to facilitate specifying S3 credentials.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Checklist

• Documentation added
• Tests updated
• Is this an important fix or new feature? Add an entry in the CHANGELOG.md.
• Changes that require user attention or interaction to upgrade are documented in docs/sources/upgrading/_index.md

[grafanabot]

./tools/diff_coverage.sh ../loki-main/test_results.txt test_results.txt ingester,distributor,querier,querier/queryrange,iter,storage,chunkenc,logql,loki

Change in test coverage per package. Green indicates 0 or positive change, red indicates that test coverage for a package fell.

+           ingester	0%
+        distributor	0%
+            querier	0%
+ querier/queryrange	0%
+               iter	0%
+            storage	0%
+           chunkenc	0%
+              logql	0%
+               loki	0%

[irizzant]

Hello @kavirajk can you please take a look at this?

[kavirajk]

@irizzant thanks for the PR. My primary concern here is empty commonEnvs by default. I'm pretty sure you are overriding commonEnvs in your environments with proper variables.

Curious why not add commonEnvs directly in our envs and overrides the pod's spec accordingly?

Something similar to

local loki = import 'lib/loki';
{
   _config+: {
        commonEnvs: [ envVar.new('AWS_CREDENTIALS')],
    }

    distributor_container+::
        container.withEnvMixin(_config.commonEnvs)

}

Same for other pod(s) containers as well.

In fact this is how we do internally to pass credentials to our pods.

[irizzant]

@kavirajk the empty array as value for commonEnvs is actually handled by withEnvMixin function, example here.
In case there are no envs already specified at pod level there is just an empty array, nothing dangerous on its own.

The reason why I didn't use the approach you suggested is to avoid the override at container level.
I think that something like:

   _config+: {
        commonEnvs: [ envVar.new('AWS_CREDENTIALS')],
    }

without having to go through all the containers to add:

somecontainer+::
        container.withEnvMixin(_config.commonEnvs)

is a more friendly approach.

[grafanabot]

./tools/diff_coverage.sh ../loki-main/test_results.txt test_results.txt ingester,distributor,querier,querier/queryrange,iter,storage,chunkenc,logql,loki

Change in test coverage per package. Green indicates 0 or positive change, red indicates that test coverage for a package fell.

+           ingester	0%
+        distributor	0%
+            querier	0%
+ querier/queryrange	0%
+               iter	0%
+            storage	0%
+           chunkenc	0%
+              logql	0%
+               loki	0%

[kavirajk]

@irizzant I'm convinced.

[kavirajk]

LGTM 👍 Thanks @irizzant