title: ngx_slab_alloc() failed: no memory in upstream zone
body: <pre><code>2017/06/29 18:37:56 [crit] 2470#2470: ngx_slab_alloc() failed: no memory in upstream zone "backends"
  2017/06/29 18:37:56 [error] 2470#2470: cannot add new server to upstream "&lt;redacted&gt;", memory exhausted
  </code></pre>
  
  <p>I am receiving a stream of critical errors in my log that indicate various upstream zones cannot be added to various upstreams because memory is exhausted.</p>
  
  <p>That said, I have plenty of free memory. I'm guessing I need to increase some setting somewhere, but for the life of me, The Google doesn't seem to be able to tell me what I need to increase.</p>
  
  <p>We use nginx as a reverse proxy for service discovery with our AWS ECS Docker container cluster.</p>