Graceful shutdown not well integrated with ProxySQL

[dveeden]

Enhancement

The graceful-wait-before-shutdown option was added in TiDB to allow for graceful shutdown of sessions.

This was intended to:

• Signal shutdown to proxys/loadbalancers/applications
• Allow for existing connections to continue to function until the timeout is hit

The problem with this is:

• ProxySQL doesn't detect the shutdown
• ProxySQL keeps sending new connections to the server
• Eventually the timeout hits and connections are dropped

Possible solutions:

1. Get ProxySQL to detect the shutdown without modifying TiDB (See https://github.com/dveeden/proxysql-tidb )
2. Make use of existing ProxySQL behavior to signal the shutdown (e.g. no longer respond OK to a ping) (see server: return error on ping when in graceful shutdown #58008 )
3. Make it easier for ProxySQL to detect the shutdown signal. This could be done by adding a server_health or shutting_down global variable.

[dveeden]

cc @renecannao

[djshow832]

It seems ProxySQL doesn't support a customized port(10080) to check the health?

[dveeden]

Closing this as #58008 was merged