Dockerfile copy running when file appears unchanged

Docker Desktop for Mac
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1

Expected behavior

dockerfile copy command should not execute when file is unchanged.

Actual behavior

on occasion, the copy command executes even though the file is apparently unchanced.

Information

  • the output of:
    • Moby Menu > Diagnose & Feedback on OSX
  • a reproducible case if this is a bug, Dockerfiles FTW
  • page URL if this is a docs issue or the name of a man page
  • host distribution and version ( OSX 10.10.x, OSX 10.11.x, Windows, etc )

Diagnostic id - C72B6511-1232-4B96-9926-EA87494D869F
OS X 10.11.5
dockerfile - https://gist.github.com/mattkime/387acee42ac494910060f6f20eea86d9

Steps to reproduce the behavior

docker run it a few times. sometimes the images will cache properly, sometimes not.

2

The issue is that the files you are copying include the Dockerfile: https://gist.github.com/mattkime/387acee42ac494910060f6f20eea86d9#file-dockerfile-L7

If you change the dockerfile, or you change the files (or anything in that directory or its children) it will invalidate your cache and any subsequent commands below it. Since the only commands you have after it are non-functional commands you may not have noticed that those too are not cached.

3

Ah, good point!

I was copying my source over early in the Dockerfile and it should be one of the last commands.

I need to work with this for a few days to verify but I’m pretty sure that was my problem.