Docker storage: volumes, bind mounts, and persistence

Data categories

Non-persistent
- Ephemeral data.
- Every container has it (the writable top layer of the image filesystem).
- Tied to the container lifecycle.
Persistent
- Volumes.
- Decoupled from individual containers.

All containers use local storage by default.
Storage locations:
- Linux: /var/lib/docker/<STORAGE-DRIVER>/
- Windows: c:\ProgramData\Docker\windowsfilter\
Common drivers by distro:
- RHEL: overlay2
- Ubuntu: overlay2 or aufs
- SUSE: btrfs
- Windows: its own driver

See Storage drivers for UnionFS driver details.

Bind mounts have existed since early Docker releases. They are more limited than volumes.

A bind mount mounts a file or directory from the host into the container.

Use them when you need to mount configuration files into a container.

Volumes use a directory under Docker’s storage path on the host. Docker manages that directory.

Use a volume for persistent data:
1. Create the volume.
2. Create your container.
Mounted to a path inside the container.
Data is written to the volume.
Deleting a container does not delete the volume.
First-class objects with their own API and subcommands.
Default local driver creates storage on the Docker host.
Third-party drivers:
- Block storage (high performance): Amazon EBS, OpenStack Cinder.
- File storage: NetApp FAS, Azure File Storage, Amazon EFS.
- Object storage (large, rarely changed files): Amazon S3, Ceph, MinIO, OpenStack Swift.
Storage locations:
- Linux: /var/lib/docker/volumes/
- Windows: c:\ProgramData\Docker\volumes