title: MongoDB to Use Sharding with $lookup Aggregation Operator
body: <p><code>$lookup</code> is new in MongoDB 3.2. It performs a left outer join to an unsharded collection in the same database to filter in documents from the “joined” collection for processing.</p>
  
  <p>To use <code>$lookup</code>, the <code>from</code> collection cannot be sharded.</p>
  
  <p>On the other hand, sharding is a useful horizontal scaling approach.</p>
  
  <p>What's the best practise to use them together?</p>