Your MongoDB write throughput is saturating a single primary. How do you scale?

Options in order of complexity: 1) Write optimization first: bulkWrite for batching, reduce document size, remove unnecessary indexes. 2) Vertical scaling: upgrade to a larger machine (quick but has limits). 3) Sharding: choose a good shard key (high cardinality + even distribution). Enable sharding on the database and collection. sh.shardCollection('db.collection', {userId: 'hashed'}) for even di