This was quite a large task and really highlighted the benefit of having tools to automate mass deployments.

We migrated from our manually created and maintained mongo database running across ec2 instances to a fully managed documentdb cluster. There were a multitude of services that needed updated to switch over to the new cluster (which there are plans further down the road to change how everything speaks to the document database) as well as the task of migrating all the data across.

Remember - communication is key, have a rollback plan, and make use of tooling (or write some) to aid in large complex operations.