question about workers and proxying to dead upstream.

[Adrian Bak]

Hey guys...

We have a setup where we serve static files from our nginx servers and
if the file doesn’t exist we proxy to a backend server (that generates
a static file, and we have another app to delete the static files when
they get to old).

The config file looks something like this (on my machine i am testing
with an apache running on port 8888):

worker_processes  1;
events {
    worker_connections  5; # 5 for testing. would be much higher in production
}

...

upstream dynamic {
        server localhost:8888;
}

location / {
            ssi on;
            try_files $uri $uri/index.html @nothere;
            break;
}

location @nothere {
            break;

            proxy_redirect on;

            # setting extra header
            proxy_set_header   X-Real-IP        $remote_addr;
            proxy_set_header   X-Forwarded-For  $proxy_add_x_forwarded_for;

            # setting timeout values for the proxying
            proxy_connect_timeout      90;
            proxy_send_timeout         90;
            proxy_read_timeout         90;

            # setting proxy buffer sizes
            proxy_buffer_size          4k;
            proxy_buffers              4 32k;
            proxy_busy_buffers_size    64k;
            proxy_temp_file_write_size 64k;

            proxy_pass http://dynamic;
    }

Anyways my question is: what happens if there are 5 (number of
worker_connection*number_worker_processes) connections to a non
existing file (it has to proxy) and the backend server times out (i
have a sleep in my php for testing purpose)?
Can nginx still serve static files (file that exist)?
Will it allow 5 connections to the upstream?

I can’t find the answer on the wiki anywhere and my own test’s with ab
and curl show that it won’t allow for 5 connections to upstream
servers if it’s hanging on one of them (it will show a “The page you
are looking for is temporarily unavailable.
Please try again later.”) - is this correct?

best,
Adrian