consistent hashing for upstreams

rmalayter nginx-forum at
Mon Mar 19 16:54:40 UTC 2012

Has anybody used ngx_http_upstream_consistent_hash with newer nginx
releases (>1.0)?

If so, is it possible to use ngx_http_upstream_consistent_hash with
HTTP-based back-ends, or does it only work with memcahe backends? The
documentation isn't at all clear.

We want to load-balance multiple static file servers behind nginx, and
basing the upstream chosen on consistent hash will drastically increase
the filesystem cache hit ratios the back-end servers, while preventing a
"thundering herd" issue when one fails. Basically you get to use all of
your RAM amongst the back ends for cache, rather than having the same
objects in the cache of multiple back end servers.

I thought of trying to use map directives and regexes to pick a back
end, but handling weighting and failover makes this a complex and
therefore brittle approach. Could consistent hashing for upstreams be
achieved with embedded lua or perl?

I know HAproxy has consistent hashing features for this use case (as do
almost all commercial load balancers), but I would prefer not adding
layers to my stack if it can be avoided. We're already using nginx and
proxy_cache and it has been rock-solid and stable for us.

Posted at Nginx Forum:,224038,224038#msg-224038

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