Hello world!
There are some issues that looks simple, stupid, however they take hours if not days to fix.
One example I had recently was with a failing docker build. “It should work! It must work!”
However, it took me I guess an hour to figure out what was wrong.
tl;dr: Prepend your docker build with
DOCKER_BUILDKIT=0and enter the last working image cache.
Buildkit 🔗
Buildkit is a Docker feature that improves the Docker backend to build images. I can’t do better than the official Docker documentation, so please have a look here.
The major improvenets I can list are improved build speed because the Docker Engine can solve the build graph in parallel: The new build uses a fully concurrent build graph solver. That’s why we have much faster builds.
However, with the new user experience, we no longer have the hashes of the built image layers. That’s a problem, because each image layer can be accessed, so the idea is to find the last built image, and run a container of that image to find issues.
How to find the issue? 🔗
The image hashes was an information available in the legacy builder. It turns out that we can temporarily build using the legacy builder: By appending our docker build with DOCKER_BUILDKIT=0, which disables Buildkit, forcing the engine to use the legacy builder.
In our example, we have:
Here we see that the last successful layer has the hash ``.
We can run into that image using docker run like the following:
Final words 🔗
Cheers,
Hassen