Updating our App

As a small feature request, we've been asked by the product team to change the "empty text" when we don't have any todo list items. They would like to transition it to the following:

You have no todo items yet! Add one above!

Pretty simple, right? Let's make the change.

Updating our Source Code

  1. In the src/static/js/app.js file, update line 56 to use the new empty text.

    -                <p className="text-center">No items yet! Add one above!</p>
    +                <p className="text-center">You have no todo items yet! Add one above!</p>
  2. Let's build our updated version of the image, using the same command we used before.

    docker build -t getting-started .
  3. Let's start a new container using the updated code.

    docker run -dp 3000:3000 getting-started

Uh oh! You probably saw an error like this (the IDs will be different):

docker: Error response from daemon: driver failed programming external connectivity on endpoint laughing_burnell 
(bb242b2ca4d67eba76e79474fb36bb5125708ebdabd7f45c8eaf16caaabde9dd): Bind for failed: port is already allocated.

So, what happened? We aren't able to start the new container because our old container is still running. The reason this is a problem is because that container is using the host's port 3000 and only one process on the machine (containers included) can listen to a specific port. To fix this, we need to remove the old container.

Replacing our Old Container

To remove a container, it first needs to be stopped. Once it has stopped, it can be removed. We have two ways that we can remove the old container. Feel free to choose the path that you're most comfortable with.

Removing a container using the CLI

  1. Get the ID of the container by using the docker ps command.

    docker ps
  2. Use the docker stop command to stop the container.

    # Swap out <the-container-id> with the ID from docker ps
    docker stop <the-container-id>
  3. Once the container has stopped, you can remove it by using the docker rm command.

    docker rm <the-container-id>

Pro tip

You can stop and remove a container in a single command by adding the "force" flag to the docker rm command. For example: docker rm -f <the-container-id>

Removing a container using the Docker Dashboard

If you open the Docker dashboard, you can remove a container with two clicks! It's certainly much easier than having to look up the container ID and remove it.

  1. With the dashboard opened, hover over the app container and you'll see a collection of action buttons appear on the right.

  2. Click on the trash can icon to delete the container.

  3. Confirm the removal and you're done!

Docker Dashboard - removing a container

Starting our updated app container

  1. Now, start your updated app.

    docker run -dp 3000:3000 getting-started
  2. Refresh your browser on http://localhost:3000 and you should see your updated help text!

Updated application with updated empty text


While we were able to build an update, there were two things you might have noticed:

  • All of the existing items in our todo list are gone! That's not a very good app! We'll talk about that shortly.
  • There were a lot of steps involved for such a small change. In an upcoming section, we'll talk about how to see code updates without needing to rebuild and start a new container every time we make a change.

Before talking about persistence, we'll quickly see how to share these images with others.