Every time I change my Dockerfile, docker re-runs all of my commands even if I change something at the end of the file. The commands are not cached.
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see also github.com/docker/docker/issues/8330Michael_Scharf– Michael_Scharf2014-10-08 15:57:57 +00:00Commented Oct 8, 2014 at 15:57
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1 Answer
In this particular case the image my image was based on contained this statement
ONBUILD ADD . /some/path
That means, no statement in my Dockerfile can be cached when my Dockerfile changes, because the ADD . /some/path is executed just before any of my statements are executed.
In general: if there is an ADD . /some/path statement in the Dockerfile no statement after that statement can be cached, because the change to the Dockerfile invalidates the cache.
My solution was to put the files I want to add into a subdirectory my_data and then add the content of the subdirectory to the path:
ADD my_data /some/path
Unfortunately, adding the Dockerfile to the .dockerignore does not help, because then the docker build cannot execute because it does not find the Dockerfile and you get the error Dockerfile was excluded by .dockerignore pattern 'Dockerfile'
3 Comments
seanmcl
Would you share why you are using ONBUILD? I've never seen a good example of this in the wild. Thanks!
Michael_Scharf
@seanmcl It is in an image that comes form docker: github.com/docker-library/python/blob/… see also registry.hub.docker.com/_/python This allows to just put your python file next to the Dockerfile and you run the app.
Elad Nava
Thanks so much. You saved me from hours of pointless rebuilding because my ADD statement was the first line in the Dockerfile.