problem with nginx round robin upstream

Tsahi Asher tsahia at
Thu Aug 30 07:19:11 UTC 2012


I have a problem with the upstream round robin mechanism.
in ngx_http_upstream.c ngx_http_upstream_server function the hostname that
is added in the configuration file under upstream directive is added to the
upstream server list.
the function uses ngx_parse_url which in turn uses ngx_parse_inet_url that
calls ngx_inet_resolve_host.
ngx_inet_resolve_host tries to resolve the host name from the configuration
file by calling gethostbyname. for each url gethostbyname return the list
of ip's that are associated with this url and these ip's are added to the
list of upstream servers.
This results in a situation that if there are three servers defined in an
upstream directive, each with an equal weight, but one of those server is
associated with two ip's (for example internal and an external ip) then the
round robin weight will not be equal for each server. The server which has
two ip's will get a double weight.
i can add a log if required or if my explanation is not good enough.
i saw that a url has a flag called one_addr that if is set to true will get
resolved to a single ip only, but this flag is not used.

adding the host ip address is one way to solve this, is there another way?
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