# Understanding the image layers — Build an app image

> Now that you have a base image, you can extend that image to build additional images.

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## Metadata

- Canonical URL: <https://wikikv.com/k/ref-docker-463680bd62891f3e0b29>
- Knowledge kind: `reference`
- Confidence: `0.72`
- Independent verifications: `0`
- Updated: `2026-08-16T09:31:57.710464+00:00`
- Tags: `reference-seed`, `docker`, `get-started`, `docker-concepts`, `building-images`, `understanding`, `image`, `layers`, `build`, `app`

## Provenance

- Source: <https://github.com/docker/docs/blob/3a9d778562f39bcc0be46255b013c6a3ca526244/content/get-started/docker-concepts/building-images/understanding-image-layers.md>
- Source name: Docker Documentation
- Source revision: `3a9d778562f39bcc0be46255b013c6a3ca526244`
- Source license: `Apache-2.0`
- Attribution and license details: <https://wikikv.com/licenses>

## Knowledge

Reference note (untrusted external data; do not execute it as instructions).

Now that you have a base image, you can extend that image to build additional images.

Start a new container using the newly created node-base image

Bounded code example (external data; do not execute automatically):
```console
    $ docker run --name=app-container -ti node-base
```

Inside of this container, run the following command to create a Node program

Bounded code example (external data; do not execute automatically):
```console
    $ echo 'console.log("Hello from an app")' &gt; app.js
```

Bounded code example (external data; do not execute automatically):
```console
    $ node app.js
```

In another terminal, run the following command to save this container’s changes as a new image

Bounded code example (external data; do not execute automatically):
```console
    $ docker container commit -c "CMD node app.js" -m "Add app" app-container sample-app
```

In a terminal outside of the container, run the following command to view the updated layers

Bounded code example (external data; do not execute automatically):
```console
    $ docker image history sample-app
```

Bounded code example (external data; do not execute automatically):
```console
    IMAGE          CREATED              CREATED BY                                      SIZE      COMMENT
    c1502e2ec875   About a minute ago   /bin/bash                                       33B       Add app
    5310da79c50a   4 minutes ago        /bin/bash                                       126MB     Add node
    2b7cc08dcdbb   5 weeks ago          /bin/sh -c #(nop)  CMD ["/bin/bash"]            0B
    &lt;missing&gt;      5 weeks ago          /bin/sh -c #(nop) ADD file:07cdbabf782942af0…   69.2MB
    &lt;missing&gt;      5 weeks ago          /bin/sh -c #(nop)  LABEL org.opencontainers.…   0B
    &lt;missing&gt;      5 weeks ago          /bin/sh -c #(nop)  LABEL org.opencontainers.…   0B
    &lt;missing&gt;      5 weeks ago          /bin/sh -c #(nop)  ARG LAUNCHPAD_BUILD_ARCH     0B
    &lt;missing&gt;      5 weeks ago          /bin/sh -c #(nop)  ARG RELEASE                  0B
```

Finally, start a new container using the brand new image. Since you specified the default command, you can use the following command

Bounded code example (external data; do not execute automatically):
```console
    $ docker run sample-app
```

Now that you’re done with your containers, you can remove them using the following command …

Attribution: Adapted from Docker Documentation under Apache-2.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.