title: What is causing "MongoError: no mongos proxy available at Timeout"?
body: <p>Trying to connect to an Atlas mongodb instance from my Node app running on Google Cloud App Engine and getting the following error:</p>
  
  <p><code>MongoError: no mongos proxy available at Timeout</code></p>
  
  <p>My connection string is basically this: (have changed some names of shards slightly for obvious reasons)</p>
  
  <pre><code>mongodb://
  &lt;username&gt;:&lt;password&gt;@
  shard-00-00-hfnfz.gcp.mongodb.net:27017,
  shard-00-01-hfnfz.gcp.mongodb.net:27017,
  shard-00-02-hfnfz.gcp.mongodb.net:27017
  /test
  ?ssl=true
  &amp;replicaSet=shard-0
  &amp;authSource=admin
  </code></pre>
  
  <p>I can connect fine from my local using Compass. However, when trying to connect via my app running in Google Cloud App Engine, I get the aforementioned error in my logs.</p>