How can I save docker container state during builds?

Question

I'm building a docker image that does a lot of apt-get installs and when one fails the container build errors and after fixing the Dockerfile docker build -t tag . will still download dependencies that were successfully installed in the first build. How can I make docker build to continue where it left off?

Answer 1

One option to consider is using separate Dockerfiles. Then you can simply use the --cache-from flag, per the documentation , to use the base image as cache.

See also: How to rebuild dockerfile quick by using cache?

Answer 2

Docker will run whole RUN commands, and caching is at that level. Usually it's beneficial to have just one RUN apt-get install line, but there's nothing actually wrong with breaking it up

FROM ubuntu:18.04
RUN apt-get update \
 && DEBIAN_FRONTEND=noninteractive \
    apt-get install package1 package2 package3
RUN apt-get update \
 && DEBIAN_FRONTEND=noninteractive \
    apt-get install package4 package5 package6

Then if something fails downloading package5 , re-running the docker build will start after the cached layer with the first three packages installed.

(If you're installing so many packages that this is routinely a problem, also consider whether you can reduce the scope of your container to something smaller that needs fewer initial downloads.)