index.md

Now that we've built an image, let's share it! To share Docker images, you have to use a Docker registry. The default registry is Docker Hub and is where all of the images we've used have come from.

Create a Repo

To push an image, we first need to create a repo on Docker Hub.

1. Go to Docker Hub and log in if you need to.

2. Click the Create Repository button.

3. For the repo name, use 101-todo-app. Make sure the Visibility is Public.

4. Click the Create button!

If you look on the right-side of the page, you'll see a section named Docker commands. This gives an example command that you will need to run to push to this repo.

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Pushing our Image

1. Back in your PWD instance, try running the command. You should get an error that looks something like this:

   $ docker push dockersamples/101-todo-app
   The push refers to repository [docker.io/dockersamples/101-todo-app]
   An image does not exist locally with the tag: dockersamples/101-todo-app
   

   Why did it fail? The push command was looking for an image named dockersamples/101-todo-app, but didn't find one. If you run docker image ls, you won't see one either.

   To fix this, we need to "tag" our image, which basically means give it another name.

2. Login to the Docker Hub using the command docker login -u YOUR-USER-NAME.

3. Use the docker tag command to give the docker-101 image a new name. Be sure to swap out YOUR-USER-NAME with your Docker ID.

   docker tag docker-101 YOUR-USER-NAME/101-todo-app

4. Now try your push command again. If you're copying the value from Docker Hub, you can drop the tagname portion, as we didn't add a tag to the image name.

   docker push YOUR-USER-NAME/101-todo-app

Running our Image on a New Instance

Now that our image has been built and pushed into a registry, let's try running our app on a brand new instance that has never seen this container!

1. Back in PWD, click on Add New Instance to create a new instance.

2. In the new instance, start your freshly pushed app.

   docker run -dp 3000:3000 YOUR-USER-NAME/101-todo-app

   You should see the image get pulled down and eventually start up!

3. Click on the 3000 badge when it comes up and you should see the app with your modifications! Hooray!

Recap

In this section, we learned how to share our images by pushing them to a registry. We then went to a brand new instance and were able to run the freshly pushed image. This is quite common in CI pipelines, where the pipeline will create the image and push it to a registry and then the production environment can use the latest version of the image.

Now that we have that figured out, let's circle back around to what we noticed at the end of the last section. As a reminder, we noticed that when we restarted the app, we lost all of our todo list items. That's obviously not a great user experience, so let's learn how we can persist the data across restarts!