### Build an app image

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

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

    ```console
    $ docker run --name=app-container -ti node-base
    ```

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

    ```console
    $ echo 'console.log("Hello from an app")' > app.js
    ```

    To run this Node program, you can use the following command and see the message printed on the screen:

    ```console
    $ node app.js
    ```

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

    ```console
    $ docker container commit -c "CMD node app.js" -m "Add app" app-container sample-app
    ```

    This command not only creates a new image named `sample-app`, but also adds additional configuration to the image to set the default command when starting a container. In this case, you are setting it to automatically run `node app.js`.

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

    ```console
    $ docker image history sample-app
    ```

    You’ll then see output that looks like the following. Note the top layer comment has “Add app” and the next layer has “Add node”:

    ```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
    <missing>      5 weeks ago          /bin/sh -c #(nop) ADD file:07cdbabf782942af0…   69.2MB
    <missing>      5 weeks ago          /bin/sh -c #(nop)  LABEL org.opencontainers.…   0B
    <missing>      5 weeks ago          /bin/sh -c #(nop)  LABEL org.opencontainers.…   0B
    <missing>      5 weeks ago          /bin/sh -c #(nop)  ARG LAUNCHPAD_BUILD_ARCH     0B
    <missing>      5 weeks ago          /bin/sh -c #(nop)  ARG RELEASE                  0B
    ```

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

    ```console
    $ docker run sample-app
    ```

    You should see your greeting appear in the terminal, coming from your Node program.

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

    ```console
    $ docker rm -f app-container
    ```

## Additional resources

If you’d like to dive deeper into the things you learned, check out the following resources:

* [`docker image history`](/reference/cli/docker/image/history/)
* [`docker container commit`](/reference/cli/docker/container/commit/)


## Next steps

As hinted earlier, most image builds don’t use `docker container commit`. Instead, you’ll use a Dockerfile which automates these steps for you.

{{< button text="Writing a Dockerfile" url="writing-a-dockerfile" >}}