How to use docker tag

When you're working with Docker, one of the commands you'll come across is docker tag. This command is pretty straightforward but super useful. It lets you give a new name, or tag, to an existing Docker image. This can be handy for organizing your images or preparing them for pushing to a Docker registry.

Let's break down how to use docker tag and why you might want to use it.

Why Use docker tag?

Imagine you've just created a Docker image, and you want to give it a more meaningful name or version number. Or maybe you want to upload it to a different registry. That's where docker tag comes in. It allows you to create an additional reference to your image without changing the original.

How to Use docker tag

The basic syntax for docker tag is:

docker tag SOURCE_IMAGE[:TAG] TARGET_IMAGE[:TAG]

Let's go through an example to make this clearer.

Example 1: Tagging an Image with a New Name

Suppose you have an image called myapp:v1. You want to give it a new name, latest-version, without losing the original tag. Here's how you'd do it:

docker tag myapp:v1 myapp:latest-version

After running this command, you'll have two tags pointing to the same image: myapp:v1 and myapp:latest-version.

Example 2: Tagging an Image for a Different Registry

Now, let's say you want to push your image to Docker Hub. You need to tag it with your Docker Hub username. If your username is johnsmith, you could do:

docker tag myapp:v1 johnsmith/myapp:v1

This creates a new tag, johnsmith/myapp:v1, which you can then push to Docker Hub.

Practical Use Case

Let's say you're developing a web application. You've built an image with your app and tagged it as webapp:development. As you're getting ready to deploy it to production, you want to tag it as webapp:production for clarity. Here's how you'd do that:

docker tag webapp:development webapp:production

Now, you can use webapp:production when you're ready to deploy your app to the production environment.

Wrapping Up

The docker tag command is a simple yet powerful tool in your Docker toolkit. It helps you manage your images by allowing you to assign multiple names or versions to the same image. Whether you're organizing your local images or preparing them for different registries, docker tag is there to help you keep everything in order.