How to Update Your Docker Image Without Starting From Scratch

Hi, it’s me here again! 👋

Ever been in this situation? You have a Docker image that you’ve been using for a while, and suddenly you need to add some new softwares. Building everything from scratch again? Nobody has time for that! 😅

Let me share a neat trick I use to save time.

1 The Situation

Let’s say I have an image called my-image (based on Ubuntu). After using it for a while, I realize I need to install some extra packages. Sure, I could modify the original Dockerfile and rebuild everything, but that would take forever! 🐌

2 The Quick Solution

Here’s a faster way to do it:

1. Create a new Dockerfile (let’s call it Dockerfile.update):

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   FROM my-image USER root RUN apt update && apt install -y your-new-package # Add more commands as needed

2. Build a new image:

   1	docker build -t my-image-new -f Dockerfile.update .

3. Play the name-swapping game:

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   # Backup old image docker tag my-image my-image-backup # Make new image the main one docker tag my-image-new my-image

4. Test it out:

   1	docker run my-image some-command

5. If everything works, clean up:

   1	docker rmi my-image-backup my-image-new

And that’s it! Your image is updated, and your disk space is clean. 🎉

3 Why This is Cool

• Much faster than rebuilding from scratch
• Safe (you have a backup if something goes wrong)
• Saves disk space after cleanup

Remember: Always test your updated image before removing the backup! Better safe than sorry! 😉

Happy Dockering! 🐳