Volumes vs networks vs Compose?

Definition:

Volumes provide storage independent of a container's disposable writable layer. Container networks define communication paths and service-name resolution, while Compose declares a set of cooperating containers and their configuration. Together they make a local multi-service setup repeatable without placing every service in one container.

Key points:

• Volumes persist data independently of a container's writable layer.

• Networks let containers communicate; localhost means that same container.

• Compose describes multiple services, networks and volumes in one configuration.

• Persisting a database volume is not a backup; deletion, corruption and operator mistakes still require a recovery plan.

Example — two Compose services:

• App service: api; database service: db; both join the same Compose network.
• The app connects to db:5432, because service-name DNS resolves the database container.
• A host mapping such as 5433:5432 lets a host client use port 5433; the app still uses port 5432 inside the network.
• Database data belongs in a volume, with a separate tested backup procedure.

Interview point:

• A database's host port is for access from outside that network; peer containers normally use the service name and container port.