First, the key terms.

Image
A template used to create a container.
Volume
Storage whose lifecycle can be independent of the container’s writable layer.

The idea, explained

Both approaches help create repeatable environments, but their isolation boundaries differ. A container image is a template; a running container also has runtime configuration, permissions and possibly persistent storage. A container’s writable filesystem is not automatically durable. Resource limits, least privilege and image updates matter. Neither packaging format makes an application secure simply by being used.

STEP 1

Locate the isolation boundary

Containers typically share the host kernel, whereas virtual machines run a guest operating system over virtualized hardware. The exact security boundary depends on the platform and configuration, not just the packaging label.

STEP 2

Plan replacement and recovery

Application containers are often replaced during upgrades. Store important data in appropriately persistent storage with backups. Never assume a new image includes the previous running instance’s database.

Follow a worked example.

A school deploys the same learning application image on two mini PCs. It stores student work in a persistent volume rather than the container’s disposable writable layer, so replacing the application does not erase that work.

Walk it through, one step at a time

  1. An offline classroom app stores completed exercises in a database.
  2. Deploy a new application image while keeping the database on a persistent volume. Verify compatibility and backup recovery before upgrading.
  3. Deleting the old container should not be the only copy of students’ work or the only rollback plan.

Where people get stuck

An image containing the application is not a backup of its live database or uploaded files.

Now try it yourself.

Pause before opening each answer. Explain your reasoning in your own words.

1. Check the core idea

Why should persistent data usually live outside a disposable container layer?

Reveal the answer & reasoning

Container replacement can discard that layer. A separate persistent storage strategy lets application upgrades and data retention have different lifecycles.

2. Apply what you learned

Does rebuilding an image restore the live data it processed?

Reveal the answer & reasoning

No. Rebuilding recreates the packaged software and included files. Runtime data needs its own persistence and recovery mechanism.