Hello, >From the current documentation it was not immediately obvious (at least to me and my colleague) that nginx does not set the $proxy_host variable to the hosts specified in an upstream block, but literally uses the name used in the proxy_pass directive.
Maxim Dounin has explained to me the reason for this [1], nevertheless I think it is worthwhile explicitly adding this behavior to the documentation. Regards Jack [1] http://mailman.nginx.org/pipermail/nginx/2018-November/057184.html
# HG changeset patch # User Jack Henschel <jack...@mailbox.org> # Date 1543937160 -3600 # Tue Dec 04 16:26:00 2018 +0100 # Node ID 4db5b4e69bc01652fec910827ce404cdeccaf104 # Parent e2e71f9477a8026c54f7c5432cd7c88865120fc9 Clarify proxy modules $proxy_host variable content >From the current documentation it was not immediately obvious that nginx does not set the $proxy_host variable to the hosts specified in an upstream block, but literally uses the name used in the proxy_pass directive. This patch clarifies this behavior. Based on the following exchange: http://mailman.nginx.org/pipermail/nginx/2018-November/057184.html diff -r e2e71f9477a8 -r 4db5b4e69bc0 xml/en/docs/http/ngx_http_proxy_module.xml --- a/xml/en/docs/http/ngx_http_proxy_module.xml Fri Nov 30 18:28:54 2018 +0300 +++ b/xml/en/docs/http/ngx_http_proxy_module.xml Tue Dec 04 16:26:00 2018 +0100 @@ -1386,6 +1386,11 @@ used in a round-robin fashion. In addition, an address can be specified as a <link doc="ngx_http_upstream_module.xml">server group</link>. +Note that nginx will stil use the name specified in the +<literal>proxy_pass</literal> directive as the +<link id="var_proxy_host"><var>$proxy_host</var>variable</link>, +not the the hostnames of the individual servers specified in the +upstream block. </para> <para> diff -r e2e71f9477a8 -r 4db5b4e69bc0 xml/en/docs/http/ngx_http_upstream_module.xml --- a/xml/en/docs/http/ngx_http_upstream_module.xml Fri Nov 30 18:28:54 2018 +0300 +++ b/xml/en/docs/http/ngx_http_upstream_module.xml Tue Dec 04 16:26:00 2018 +0100 @@ -47,6 +47,11 @@ } } </example> +Note that in the above example nginx will use the name specified in the +<link doc="ngx_http_proxy_module.xml" id="proxy_pass">proxy_pass</link> +directive as the <link doc="ngx_http_proxy_module.xml" id="var_proxy_host"> +<var>$proxy_host</var> variable</link>, not the the hostnames of the +individual servers specified in the upstream block. </para> <para>
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