

Zero-Downtime Restarts with HAProxy - bdotdub
http://www.igvita.com/2008/12/02/zero-downtime-restarts-with-haproxy/

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jbyers
An interesting method, but as the comments say, getting your load balancer or
proxy to do the right thing is the tip of the iceberg. Migrating your database
on the fly requires schema version-aware code, facilities for split-brain
upgrades (e.g. with mmm MySQL), sensible handling of in-progress requests. All
that gets costly in terms of development time and complexity that, unless
you're really big or run a critical-availability service (from hospital down
to ad serving), is arguably better used making your product better. Just eat
the few minutes of downtime after setting your customers' expectations
properly.

