title: nginx 'invalid number of arguments in "map" directive'
body: <p>I'm trying to reverse-proxy a websocket, which I've done with nginx before with no issue. Weirdly, I can't seem to re-create my prior success with something so simple. I've been over and over the config file but can't seem to find my error.</p>
  
  <p>Here's my full <code>default.conf</code>:</p>
  
  <pre><code>map $http_upgrade $connection_upgrade {
      default upgrade;
      '' close;
  }
  
  server {
    listen 80;
  
    location /api/ {
      proxy_pass ${API_LOCATION};
    }
  
    location / {
      proxy_pass ${UI_LOCATION};
      proxy_http_version 1.1;
      proxy_set_header Upgrade $http_upgrade;
      proxy_set_header Connection $connection_upgrade;
    }
  }
  </code></pre>
  
  <p>The error I'm getting:</p>
  
  <pre><code>2016/10/10 23:30:24 [emerg] 8#8: invalid number of arguments in "map" directive in /etc/nginx/conf.d/default.conf:1
  nginx: [emerg] invalid number of arguments in "map" directive in /etc/nginx/conf.d/default.conf:1
  </code></pre>
  
  <p>And the exact Dockerfile that I'm using, in case you want to replicate my setup (save <code>default.conf</code> as <code>conf.templates/default.conf</code> relative to the Dockerfile:</p>
  
  <pre><code>FROM nginx
  COPY conf /etc/nginx/conf.templates
  CMD /bin/bash -c "envsubst &lt; /etc/nginx/conf.templates/default.conf &gt; /etc/nginx/conf.d/default.conf &amp;&amp; nginx -g 'daemon off;'"
  </code></pre>