Description of Linked Ticket

Before to create a sharded collection it is currently required to invoke the enableSharding command. This command doesn't really do much apart from setting a flag in config.databases, that is only consumed by the shardCollection command.

This additional step is not very useful and not really required in order to create a sharded collection, additionally it contributes to make the sharding experience more complicated than than the replica set one without any real benefit.

This ticket contain a proposal to make the enableSharding command optional and to deprecate it.

Proposal:

• It won't be necessary anymore to call enableSharding  before to shard a collection. 
• We will still keep support for enableSharding command  because users are using it to select the database primaryShard before to create a collection. So enableSharding  will really behave like a "createDatabase" that you can use if you want to create a database with specific options, otherwise default options will be chosen automatically on the implicit creation (like the primarShard). 
• Additionally the name "enableSharding" will become misleading since it won't really "enable sharding" anymore, so we will introduce a new  createDatabase command as an alias of the old enableSharding. In this sense the new  createDatabase  command will be very similar to createCollection , it will be optional but you can use it to specify particular options for database creation.