IT 3300 : Virtualization

Docker — Storage

The problem

• A container's writable layer is ephemeral
• Remove the container and that data is gone
• Databases, uploads, logs need to outlive the container

Three ways to persist

• Volumes — Docker-managed storage (the default choice)
• Bind mounts — map a specific host path into the container
• tmpfs — in-memory only, nothing written to disk

Volumes

• Managed by Docker under its own directory

• Portable across containers; easy to back up

• Best for databases and app data

Bind mounts

• Map a host directory straight into the container

• Great for development — edit on the host, see it live inside

• You control the exact host path (and its permissions)

Volumes vs. bind mounts

• Volume — Docker owns the location; portable; production data
• Bind mount — you own the path; tied to the host; dev workflows
• tmpfs — sensitive/scratch data that should never hit disk

Inspecting and cleaning

• docker volume ls — list volumes
• docker volume inspect data — where it lives, who uses it
• docker volume rm data — remove (must be unused)
• docker volume prune — remove all unused volumes (careful)

Lab goals

• Run a database with a named volume; write data; recreate the container
  and confirm the data survived
• Use a bind mount to serve a local folder with nginx and edit it live