Use stats database for proxysql backends count

[aymeric-ledizes]

What does this PR do?

This PR will change the query for the proxysql.backends.count metric from a query in a runtime table (admin-admin_credentials required) to a query in a stats table (allowing admin-stats_credentials only)

Motivation

Query in the runtime_mysql_servers table require admin credential by default. Runtime tables such as runtime_mysql_users contains sensitive data so it is not recommended to use admin-admin_credentials nor grant permissions.

While we can get the relevant data about backends count from the stats table stats_mysql_connection_pool we can update the query to this table instead.

Additional Notes

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• PR title must be written as a CHANGELOG entry (see why)
• Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• PR must have changelog/ and integration/ labels attached

[codecov]

Codecov Report

Merging #12555 (b5653bc) into master (1e32d0f) will not change coverage.
The diff coverage is n/a.

Flag	Coverage Δ
proxysql	98.97% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

[frivoire]

I just checked and I confirm @aymeric-ledizes's analysis:
=> using the (unprivileged) stats user, the (old) table is not accessible, and your "new" table is working fine

cf: this test on my proxysql admin socket:

$ mysql -ustats -pstats -h127.0.0.1 -P6032
mysql> show tables;
+--------------------------------------+
| tables                               |
+--------------------------------------+
| global_variables                     |
| stats_memory_metrics                 |
| stats_mysql_commands_counters        |
| stats_mysql_connection_pool          |
| stats_mysql_connection_pool_reset    |
| stats_mysql_errors                   |
| stats_mysql_errors_reset             |
| stats_mysql_free_connections         |
| stats_mysql_global                   |
| stats_mysql_gtid_executed            |
| stats_mysql_prepared_statements_info |
| stats_mysql_processlist              |
| stats_mysql_query_digest             |
| stats_mysql_query_digest_reset       |
| stats_mysql_query_rules              |
| stats_mysql_users                    |
| stats_proxysql_servers_checksums     |
| stats_proxysql_servers_metrics       |
| stats_proxysql_servers_status        |
+--------------------------------------+

mysql> SELECT  hostgroup_id, status, COUNT(*) FROM runtime_mysql_servers GROUP BY hostgroup_id, status;
ERROR 1045 (28000): ProxySQL Admin Error: no such table: runtime_mysql_servers

mysql> SELECT  hostgroup, status, COUNT(*) FROM stats_mysql_connection_pool GROUP BY hostgroup, status;
+-----------+---------+----------+
| hostgroup | status  | COUNT(*) |
+-----------+---------+----------+
| 10        | ONLINE  | 1        |
| 10        | SHUNNED | 4        |
| 20        | ONLINE  | 4        |
| 30        | ONLINE  | 4        |
+-----------+---------+----------+

NB: of course, the "new" query also works with an "admin" user, so no regression :)

So, this change should only improve the usability & security of this integration 👍

[aymeric-ledizes]

Hello @hithwen, is this small PR ok to be merged ?

[FlorentClarret]

Hi! Thanks for your contribution!

I left some comments. Basically, you can simply update the query and it should be fine.

[FlorentClarret]

Thank you!