Nginx response with persistence session and backend server failure

Bhuvan Gupta bhuvangu at
Mon Jul 27 07:10:04 UTC 2015

Hello all,

I was reading Nginx documentation
persistence session using cookie and below is from documentation

A request that comes from a client not yet bound to a particular server is
passed to the server selected by the configured balancing method. Further
requests with this cookie will be passed to the designated server. *If the
designated server cannot process a request*, *the new server is selected as
if the client has not been bound yet*.

The last line says that

*If the designated server cannot process a request*.

What does it mean to say "the server cannot process a request."

Question 1:
Does it mean the server was down ?
or does it mean server responded with some error code ?
or does it mean that it did not responded in a certain time interval ?
or does it mean that max number of connection limit is reached on that
server ?

Question 2:
Let say there were 3 backend-server and we are using session persistence
using cookie.
Now assume that 2 of the backed server goes down so niginx will route all
request to 3rd server
Now 2 other server came back online, will niginx use the other 2 server to
route the request even if request have the persistence cookie for 3rd

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