Pushing images to registry in Docker - Commands & Configuration

Introduction

When you build a container image on your computer, it stays local. To share it with others or use it on servers, you need to upload it to a central place called a registry. Pushing images to a registry lets you store and share your container images easily.

When you want to share your app's container image with your team.

When you need to deploy your container image to a cloud server.

When you want to keep a backup of your container images online.

When you want to use the same container image on multiple machines.

When you want to automate deployments using images stored in a registry.

Commands

This command builds a container image from the current folder and tags it as 'my-app' with version '1.0'. Tagging helps identify the image later.

Terminal

docker build -t my-app:1.0 .

Expected Output

Sending build context to Docker daemon  2.048kB

Step 1/3 : FROM alpine

 ---> a24bb4013296

Step 2/3 : RUN echo "Hello from my app"

 ---> Running in 123abc456def

Removing intermediate container 123abc456def

 ---> 789def012ghi

Step 3/3 : CMD ["echo", "Hello from my app"]

 ---> Running in 456ghi789jkl

Removing intermediate container 456ghi789jkl

 ---> 345jkl678mno

Successfully built 345jkl678mno

Successfully tagged my-app:1.0

→

-t - Tags the image with a name and version

This command tags your local image with the registry address so Docker knows where to push it.

Terminal

docker tag my-app:1.0 myregistry.example.com/my-app:1.0

Expected Output

No output (command runs silently)

This command logs you into the registry so you have permission to upload images. It will ask for your username and password.

Terminal

docker login myregistry.example.com

Expected Output

Username: user123

Password: 

Login Succeeded

This command uploads your tagged image to the registry so others can download and use it.

Terminal

docker push myregistry.example.com/my-app:1.0

Expected Output

The push refers to repository [myregistry.example.com/my-app]

1.0: Pushed

Digest: sha256:abcdef1234567890abcdef1234567890abcdef1234567890abcdef1234567890

Status: Image is up to date for myregistry.example.com/my-app:1.0

This command lists all local images so you can verify your image is built and tagged correctly.

Terminal

docker images

Expected Output

REPOSITORY                          TAG       IMAGE ID       CREATED          SIZE

my-app                             1.0       345jkl678mno   2 minutes ago    5MB

myregistry.example.com/my-app      1.0       345jkl678mno   2 minutes ago    5MB

Key Concept

If you remember nothing else from this pattern, remember: tag your image with the registry address before pushing it so Docker knows where to upload.

Common Mistakes

Trying to push an image without tagging it with the registry address.

Docker does not know where to send the image, so the push fails.

Use 'docker tag' to add the registry address to your image before pushing.

Not logging into the registry before pushing.

The registry denies permission, so the push is rejected.

Run 'docker login' with the registry URL and enter your credentials first.

Using 'latest' tag unintentionally when pushing.

It can cause confusion about which version is deployed or used.

Always tag images with explicit version numbers like '1.0' to avoid ambiguity.

Summary

Build your container image locally and tag it with a name and version.

Tag the image again with the registry address to prepare for upload.

Log in to the registry to authenticate your push.

Push the tagged image to the registry so it can be shared or deployed.

Verify your images locally to confirm tagging and building.