Make credential structure used for monitoring configurable

[toabi]

I'm migrating to the integrated monitoring because of #138

I see the following issues:

Duplicate definition of admin secrets

Not a big deal, just a bit duplication of code when using existingAdminSecret. Monitoring templates will just look at adminUserSecret. If the existing one is defined, it could use that one?

Structure of secret hardcoded

For some reason, while existingAdminSecret works, the same secret doesn't for the pg_exporter.

I'm using the zalando postgres operator and it creates secrets with username and password as keys. The monitoring pod expects user and password:

db-operator/charts/db-instances/templates/postgres_exporter.yaml

Lines 36 to 39 in 27daa92

	- name: DATA_SOURCE_PASS_FILE
	value: /run/secrets/db-secrets/password
	- name: DATA_SOURCE_USER_FILE
	value: /run/secrets/db-secrets/user

If I'm not mistaken, the operator itself has a fallback to use the "postgres" user in that case, which apparently works in my setup:

https://github.com/kloeckner-i/db-operator/blame/aefb00fb1ac9e37db02706f7e2209c8c26e7a23e/pkg/utils/database/postgres.go#L356-L365

Changing the secret in the operator is not possible yet: zalando/postgres-operator#1746

[toabi]

Do you think it would be feasible to make the password-key and username-key configurable in the helm chart values?

Because changing the value from .../db-secrets/user to .../db-sercerts/username manually in the deployment makes it all work nicely.

I imagine it could be set as exporter.postgres.secret.password_key and exporter.postgres.secret.user_key which default to the current values but could then be overridden.

[toabi]

db-operator/charts/db-instances/templates/postgres_exporter.yaml

Lines 34 to 35 in 27daa92

	- name: DATA_SOURCE_URI
	value: dbinstance-{{ $name }}-svc:5432/postgres?sslmode=disable

This would also have to be configurable, because the zalando operator builds the service name differently from the $name (without prefix and suffix) and additionally zalandos default pg_hba only allows SSL connections from non-localhost.

[toabi]

Would you accept a Pull Request which makes the user and password key and the DATA_SOURCE_URI more configurable or do you plan to change this yourself? // CC @sookloeckner , @hyunysmile