Images are good and fine, but eventually you'll need a way to share them with people or systems so that they can be executed or deployed. Docker uses mechanisms like docker tag and docker push to make this happen.
First off, you can see the tags that you currently have by running docker images. The output should look like this:
REPOSITORY TAG IMAGE ID CREATED SIZE
banana-smith-image latest 98be87baf87e 28 seconds ago 17.8MB
hello-world latest fce289e99eb9 3 weeks ago 1.84kB
busybox latest 3a093384ac30 3 weeks ago 1.2MB
nginx latest 7042885a156a 4 weeks ago 109MB
The latest tag gets appended to the latest build of a particular image name. However, you can add more tags to that image ID by running:
docker tag 98be87baf87e banana-smith-image:tag-2
Where you can replace 98be87baf87e with the IMAGE ID of your image. Now, if you run docker images, you should see:
REPOSITORY TAG IMAGE ID CREATED SIZE
banana-smith-image tag-2 98be87baf87e 28 seconds ago 17.8MB
banana-smith-image latest 98be87baf87e 28 seconds ago 17.8MB
hello-world latest fce289e99eb9 3 weeks ago 1.84kB
busybox latest 3a093384ac30 3 weeks ago 1.2MB
nginx latest 7042885a156a 4 weeks ago 109MB
Note that you can also use repositories and tags as a source image. For example:
docker tag banana-smith-image:latest banana-smith-image:tag-3
Now, when you run docker images, you should get:
REPOSITORY TAG IMAGE ID CREATED SIZE
banana-smith-image tag-3 98be87baf87e 28 seconds ago 17.8MB
banana-smith-image tag-2 98be87baf87e 28 seconds ago 17.8MB
banana-smith-image latest 98be87baf87e 28 seconds ago 17.8MB
hello-world latest fce289e99eb9 3 weeks ago 1.84kB
busybox latest 3a093384ac30 3 weeks ago 1.2MB
nginx latest 7042885a156a 4 weeks ago 109MB
Now your image has three tags. Note that you can use tags as a way of referencing where to upload your images, but we'll tackle that later.
Docker repositories allow you to share your images with the community. To get started, we'll create a repository by going to Docker Hub and selecting Create A Repository:
Name it however you want. In the below example, we're calling it /my-first-repo:
We're setting it to Private.
Now, remember the images we had earlier? We're going to add a tag - except the tag will be your Docker Hub username, and the repository you have created:
docker tag banana-smith-image:latest banana-smith/my-first-repo
Where banana-smith is your Docker Hub username. Finally, we'll login to Docker Hub with the following command:
docker login
Use your Docker Hub credentials to login. Once you're logged in, you can push your image to Docker Hub:
docker push banana-smith/my-first-repo
Now, we can check if we've uploaded our image to Docker hub. With your browser, go to your Docker Hub repository and check under Tags. Do you see your image?
To verify that your image can be pulled down, you can try running:
docker pull banana-smith/my-first-repo
Now that you know how to login and push images, try creating a Public repository and pushing an image to it. Ask the person next to you to pull the image down and run it.