Deprecate syslogging

[sougou]

There is old code in vitess that invokes syslog. This has mostly been problematic:

• Most containers don't have syslog enabled.
• It was known to have caused unnecessary disk I/O.
• No one knows it exists. So, it's unused.

I recommend we delete this:

• delete go/cmd/vttablet/plugin_sysloglogger.go
• delete package go/event/syslogger

This most likely changes all those event logging invocations to be no-ops. We can retain those calls and later find a better plugin than syslog.

[aquarapid]

There is actually syslog-referencing code all over the code-base, as you mentioned:

$ grep -r syslog * | cut -d: -f1 | sort -u | grep go$
go/cmd/vtctl/vtctl.go
go/cmd/vttablet/plugin_sysloglogger.go
go/event/syslogger/syslogger.go
go/event/syslogger/syslogger_test.go
go/vt/topo/events/keyspace_change_syslog.go
go/vt/topo/events/keyspace_change_syslog_test.go
go/vt/topo/events/shard_change_syslog.go
go/vt/topo/events/shard_change_syslog_test.go
go/vt/topo/events/tablet_change_syslog.go
go/vt/topo/events/tablet_change_syslog_test.go
go/vt/topotools/events/migrate_syslog.go
go/vt/topotools/events/migrate_syslog_test.go
go/vt/topotools/events/reparent_syslog.go
go/vt/topotools/events/reparent_syslog_test.go
go/vt/vttablet/filelogger/filelogger.go
go/vt/vttablet/sysloglogger/sysloglogger.go
go/vt/vttablet/sysloglogger/sysloglogger_test.go
go/vt/worker/events/split_syslog.go
go/vt/worker/events/split_syslog_test.go

I think we should keep it and document it more prominently. My arguments:

• it is still potentially useful in non-container environments
• if it causes unnecessary disk I/O is an implementation detail of the underlying syslog implementation? A properly configured and managed syslog subsystem wouldn't cause any local disk I/O and just stream the logs off-machine continuously.
• syslog is still a lowest-common-denominator; all the other logging "standards"/tools have something to convert from syslog to their formats

[sougou]

But it could cause problems for someone who doesn't know that it's turned on right? How about turning this off by default, and let those who want it turn it on.

[derekperkins]

I'm totally behind disabling it by default

[makmanalp]

We (HubSpot) also vote to either nuke it or have an option to disable it. Right now it either prints out an error message we don't care about, or we have to do some hackery to shut it up.

[tspotts]

Agree with what @makmanalp stated above, it would be nice to disable syslog OR have it be opt-in. We've had to implement a few hacks to silence the warnings in our CI/CD pipeline.