

Deploy your site without downtime using a web proxy written in node.js - bguthrie
http://pgrs.net/2010/2/1/web-proxy-in-node-js-for-high-availability

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forkqueue
If you're using Varnish for caching then it's also possible to serve 'stale'
cache entries whilst the upgrade is being done.

I have a few customers that use this when doing schema changes. Obviously,
this relies on cached data being useful for your site, but for many
applications a stale cache is massively preferable to an error message.

<http://varnish-cache.org/wiki/VCLExampleGrace>

