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copied!<p>EDIT: I do see in the original question that there was no problems running under Linux, however, I was facing difficulties on Linux as well, under "high load" scenarioes (i.e +50 concurrent requests) so this might apply to OS X as well...</p> <p>I dug a little deeper into this problem and I found a solution to my setup - I'm no longer recieving 502 Bad Gateway errors when load testing my simple hello world application. I tested everyting on Ubuntu 13.10 with a fresh compile of Mono 3.2.3 installed in /opt/mono.</p> <p>When you start the mono-fastcgi-4 server with "/verbose=True /printlog=True" you will notice the following output:</p> <pre><code>Root directory: /some/path/you/defined Parsed unix:/tmp/nginx-1.sockets as URI unix:/tmp/nginx-1.sockets Listening on file /tmp/nginx-1.sockets with default permissions Max connections: 1024 Max requests: 1024 </code></pre> <p>The important lines are "max connections" and "max requests". These basically tells how many active TCP connections and requests the mono-fastcgi server will be able to handle - in this case 1024.</p> <p>My NGINX configuration read:</p> <pre><code>worker_processes 4; events { worker_connections 1024; } </code></pre> <p>So I have 4 workers, <em>which each can have 1024 connections</em>. Thus NGINX happily accepts 4096 concurrent connections, which are then sent to mono-fastcgi (who only wishes to handle 1024 conns). Therefore, mono-fastcgi is "protecting it self" and stops serving requests. There are two solutions to this:</p> <ol> <li>Lower the amount of requests that NGINX can accept</li> <li>Increase your fastcgi upstream pool</li> </ol> <p>1 is trivially solved by changing NGINX configuration to read something like:</p> <pre><code>worker_processes 4; # <-- or 1 here events { worker_connections 256; # <--- if 1 above, then 1024 here } </code></pre> <p>However, this could verly likely mean that you're not able to max the resources on your machine. </p> <p>The solution to 2. is a bit more tricky. First, mono-fastcgi must be started multiple times. For this I created the following script (inside the website that should be started):</p> <pre><code>function startFastcgi { /opt/mono/bin/fastcgi-mono-server4 /loglevels=debug /printlog=true /multiplex=false /applications=/:`pwd` /socket=$1 & } startFastcgi 'unix:/tmp/nginx-0.sockets' startFastcgi 'unix:/tmp/nginx-1.sockets' startFastcgi 'unix:/tmp/nginx-2.sockets' startFastcgi 'unix:/tmp/nginx-3.sockets' chmod 777 /tmp/nginx-* </code></pre> <p>Which starts 4 mono-fastcgi workers that can each accept 1024 connections. Then NGINX should be configured something like this:</p> <pre><code>upstream servercom { server unix:/tmp/nginx-0.sockets; server unix:/tmp/nginx-1.sockets; server unix:/tmp/nginx-2.sockets; server unix:/tmp/nginx-3.sockets; } server { listen 80; location / { fastcgi_buffer_size 128k; fastcgi_buffers 4 256k; fastcgi_busy_buffers_size 256k; fastcgi_pass servercom; include fastcgi_params; } } </code></pre> <p>This configures NGINX with a pool of 4 "upstream workers" which it will use in a <a href="http://nginx.org/en/docs/http/ngx_http_upstream_module.html" rel="noreferrer" title="round-robin fashion">round-robin fashion</a>. Now, when I'm hammering my server with <a href="https://github.com/tarekziade/boom" rel="noreferrer" title="Boom">Boom</a> in concurrency 200 for 1 minute, it's all good (aka no 502 at all).</p> <p>I hope you can somehow apply this to your code and make stuff work :)</p> <p>P.S:</p> <p>You can download my Hello World ServiceStack code that I used to test <a href="https://github.com/nover/service-stack-fastcgi-heroku" rel="noreferrer" title="here">here</a>.</p> <p>And you can download my full NGINX.config <a href="http://ge.tt/5xxs8Ry/v/0%20here" rel="noreferrer">here</a>.</p> <p>There are some paths that needs to be adjusted though, but it should serve as a good base.</p>

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