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Say, I have a local dir structure of /var/lib/jenkins and on the resultant container i have the same dir stucture. Now, i need that the jenkins user created through Dockerfile should be able to access the /var/lib/jenkins/.m2/repository existing on local machine. I have mapped the container jenkins userid to the jenkins userid on local using usermod and groupmod in Dockefile. However, I need that /var/lib/jenkins/.m2/repository on local should be accessible inside the container for all processes on it, in a way that local machines's repository maps to container path

Effectively, i need to achieve below cmd inside the dockerfile

docker run -it  --name my_container -v /var/lib/jenkins/.m2/repository:/var/lib/jenkins/.m2/repository my_image

Any guidance on this will be helpful.

Thanks!

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You cannot define a volume source in a Dockerfile, because images may be run on different environments where the source would change. So while you can tell Docker the image has a volume at /var/lib/jenkins/.m2/repository, you cannot tell the image to map that volume to the host directory /var/lib/jenkins/.m2/repository. To specify runtime configurations, you can specify this in a docker-compose.yml file with a volume section like:

version: '3'
services:
  svcname:
    image: my_image
    volumes:
    - /var/lib/jenkins/.m2/repository:/var/lib/jenkins/.m2/repository

I personally recommend against defining a volume inside the Dockerfile. It will generate anonymous volumes if you don't also specify a volume source at runtime. And if you want to make changes to this directory with a RUN command in your Dockerfile after the volume is defined, those changes will not be saved to your image and will be lost when the RUN line completes.

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  • Thanks, @BMitch, for explaining so well. Cleared all doubts. I also do not favor defining volume inside Dockerfiles as it defeats the purpose of Docker portability. However, I was trying to use the mvn repos already downloaded on host to use in the container......But yes, docker compose is the right way to go for this usecase so far. – Valencia Serrao Aug 23 '18 at 11:12
  • I could only accept your answer @BMitch. I am unable to upvote due to StackExchange reputation criteria. – Valencia Serrao Aug 23 '18 at 11:15
  • @ValenciaSerrao if you're looking for the option to have a cache directory on the build host, that functionality is coming with buildkit: github.com/moby/moby/issues/32507#issuecomment-409092581 – BMitch Aug 23 '18 at 11:23
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Yes, it is, you can use VOLUME directive, in your example line will looks like

VOLUME /var/lib/jenkins/.m2/repository

detailed description in documentation

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  • Thanks, @Quantim for responding. Yes. I had tried this instruction earlier too, it only creates an empty directory in the container. It still needs to use 'docker run -it -v ' to be able to access the host path. This is confirmed in another post here (see accepted answer: stackoverflow.com/questions/27735706/docker-add-vs-volume) – Valencia Serrao Aug 23 '18 at 11:03

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