verified using server docker - perconalab/pmm-server-fb:PR-3397-987dfa0
client docker - perconalab/pmm-client-fb:PR-3397-987dfa0
client - https://s3.us-east-2.amazonaws.com/pmm-build-cache/PR-BUILDS/pmm2-client/pmm2-client-PR-3397-987dfa0.tar.gz

I bumped up the version in the regexp - it simply went out of date since this PR didn't make it to 2.40.0.

It's verified on agent versions: 2.41.0, 2.40.0, and 2.36 as per the logs below:

I gave mysql a thorough test because it's special in that the agent must return the table count, while the others don't. However, it's a great idea to test adding other databases as well

User impact:
The user is not able to add any database to monitoring using released pmm-client

Preconditions:

• Start PMM Server (perconalab/pmm-server-fb:PR-3397-aecc08f)

• Setup pmm-client 2.40.0

• Setup Percona server DB

Steps to reproduce:

1. run pmm-admin add mysql --username={username} --password={password} --port={port}

Actual results:

• Internal server error. is shown to the user

Expected result:

• The user should see a success message and should see service details.

Note: 

• attached logs from pmm-server

A quick note on possible implementation

An ad-hoc investigation revealed that the database engine version is available from metrics. The following metrics are currently provided by the exporters:

• mongodb_version_info

• mysql_version_info

• pg_static

However, when we query the information from the database, we would need to make as many calls to VictoriaMetrics as there are services, which would be too slow on a system with a good number of monitored services. Therefore, from a performance standpoint it would be nice to store the database engine version in the state. To avoid staleness, we can re-query the version from VM whenever an inventory endpoint that mutates the service record is called.

If not the above, then we could ask pmm-agent for the database version. However, it seems like we still need to figure out how pmm-agent can reliably query it from different db engines.