Add support for SO_REUSEPORT to vtgate

[rjlaine]

Description

Add an option to bind ports with SO_REUSEPORT on unix builds of vtgate. SO_REUSEPORT is a unix socket option which allows multiple processes running under the same UID to bind the same port at the same time. The kernel then load balances traffic between all processes listening on the port. This option can be utilized by users who want to update vtgates in place without service interruption, or to hot-reload configuration.

Related Issue(s)

• Closes: RFC: SO_REUSEPORT #19101
• Relates to: Add reuse-port flag to vtgate docs website#2061

Deployment Notes

No-op unless the new flag is set. The new flag can be used with existing config, without additional configuration changes. However, for users that want to utilize it for hot reload config, additional changes will be required in their specific runtime environment. For a very minimal example, to run hot reloading in a systemd service template, you might set up something like this:

/etc/systemd/system/vtgate@.service

[Unit]
Description=vtgate %i
After=network.target

[Service]
User=vitess
ExecStart=/usr/local/bin/vtgate --mysql_server_port=3306 --reuse-port
ExecStartPost=/bin/sh -c '/bin/systemctl stop vtgate@$(( %i ^1 ))'

And then toggle between the two to hot reload:

i=$(( i ^1 ))
systemctl restart "vtgate@${i}"

[vitess-bot]

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

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• Ensure that the Pull Request has a descriptive title.
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• vtctl command output order should be stable and awk-able.

[promptless]

📝 Documentation updates detected!

New suggestion: Add changelog entry for VTGate --reuse-port flag

[promptless]

📝 Documentation updates detected!

New suggestion: Document vtgate --reuse-port flag for zero-downtime updates

[codecov]

Codecov Report

❌ Patch coverage is 56.75676% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.95%. Comparing base (ed22ed7) to head (a65beb0).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vtgate/plugin_mysql_server.go	0.00%	7 Missing ⚠️
go/netutil/reuseport_unix.go	76.47%	4 Missing ⚠️
go/vt/servenv/listen.go	62.50%	3 Missing ⚠️
go/mysql/server.go	66.66%	1 Missing ⚠️
go/vt/servenv/run.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #19168   +/-   ##
=======================================
  Coverage   69.95%   69.95%           
=======================================
  Files        1610     1612    +2     
  Lines      216083   216112   +29     
=======================================
+ Hits       151159   151190   +31     
+ Misses      64924    64922    -2     

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[rjlaine]

Is it normal for CI to fail? I merged the latest commits from main, and these 2 tests continue to fail. They don't appear related to my change, but I might be missing something.

[mattlord]

Is it normal for CI to fail? I merged the latest commits from main, and these 2 tests continue to fail. They don't appear related to my change, but I might be missing something.

You will have to merge in main after this is merged shortly: #19198

[timvaillancourt]

LGTM, just pointed out one linter problem

[mattlord]

@rjlaine I apologize for the delay! Can you please merge in origin/main? The new required tests should then run and pass and we can get this merged. ❤️