Microservice Application … Docker Volume for Databases or no Docker Volume?

I have an application (JHipster Gateway, UAA, Registry, 5 microservices) and each application source builds a Docker image and pushes to GitLab registry. Currently I’m running everything on Rancher using a Docker-Compose file. My volumes for Mongo databases are currently in each container.

I need advice about volume mounts. Here are my options as I see them.
1. Leave data in containers and monitor and backup
2. Use external mounts and monitor volumes on host.

If I leave Mongo data in the containers, do I just set up to just cluster and when the internal volumes fill, the database just scales? I am looking for some explanation to help my choice with Mongo database mounts, internal or external (on host)?

Thanks in advance,

David L. Whitehurst

Source: StackOverflow