Behavior between upstream hash and backup

[Maxim Dounin]

Hello!

On Wed, Jan 11, 2017 at 04:27:51PM -0500, Jonathan Simowitz via nginx wrote:

> Hello,
> 
> I would like to define an upstream block with a number of servers and
> utilize the hash directive to choose a particular server dependent on the
> request. There is a chance that the chosen server could fail and so I would
> also like to configure a backup server to handle the request in this case.

If there are more than one server in the upstream block, the 
default behaviour is to try another server if a choosen one fails, 
see http://nginx.org/r/proxy_next_upstream.  The exact algorithm 
to select "another server" varies depending on the balancing 
algorithm used - e.g., in case of "hash .. consistent" it means 
selecting the next point in the continuum, like if the failed 
server was removed from the list.

> If I define an additional server in this upstream and declare it as backup
> will it handle the request if the hash-chosen server fails as defined by my
> proxy_next_upstream directive?

No, backup servers are not supported by the hash balancer.

-- 
Maxim Dounin
http://nginx.org/