Debugging failed builds

[peterwaller-arm]

I have a build step which takes a long time to run (imagine, e.g. hours). Sometimes it fails.

It would be nice when that happens if the image continued to be around, so I could:

• Go and dig out logs which the build machinery saves into /tmp/...buildfailure...log. (This is unpredictable and unconfigurable, since there are quite a number of things going on in the build.)
• Quickly go in and run commands in the same failing context, without having to repeat ~hours worth of build to get to the point of failure.

I might have expected an option like --keep-failed, but I didn't yet find it.

[tonistiigi]

moby/buildkit#1472