title: Which MQTT server for > 1M connections
body: <p>With a budget of perhaps a few million to setup a MQTT server farm how would you do so?  </p>
  
  <p>It must have the following properties:</p>
  
  <ul>
  <li>Support for 4-5M connections across all data centers.</li>
  <li>300k msg/s of around 1kb each</li>
  <li>Geographic redundancy</li>
  <li>Can't lose messages QOS1</li>
  <li>Each client will publish to a single topic but subscribe to their own unique topic.  This implies 4-5 million topics.</li>
  </ul>
  
  <p>MQTT Server brokers can be found here:
  <a href="https://github.com/mqtt/mqtt.github.io/wiki/server-support#capabilities" rel="noreferrer">https://github.com/mqtt/mqtt.github.io/wiki/server-support#capabilities</a></p>
  
  <p>However capabilities are usually not published.</p>