Sharding is MongoDB's solution for horizontal scaling. In Chapter 8, Monitoring, Backup, and Security, we will go over its usage in more detail, but the following are some best practices, based on the underlying data architecture:

• Think about query routing: Based on different shard keys and techniques, the mongos query router may direct the query to some (or all) of the members of a shard. It is important to take our queries into account when designing sharding, so that we don't end up with our queries hitting all of our shards.
• Use tag-aware sharding: Tags can provide more fine-grained distribution of data across our shards. Using the right set of tags for each shard, we can ensure that subsets of data get stored in a specific set of shards. This can be useful for data proximity between application servers, MongoDB shards, and the users.