Use an ARG in Dockerfile FROM for dynamic image specification
Dockerfile
s have been able to use ARG
s to allow passing in parameters during a docker build
using the CLI argument --build-arg
for some time. But until recently (Docker's 17.05 release, to be precise), you weren't able to use an ARG
to specify all or part of your Dockerfile
's mandatory FROM
command.
But since the pull request Allow ARG in FROM was merged, you can now specify an image / repository to use at runtime. This is great for flexibility, and as a concrete example, I used this feature to allow me to pull from a private Docker registry when building a Dockerfile in production, or to build from a local Docker image that was created as part of a CI/testing process inside Travis CI.
To use an ARG
in your Dockerfile
's FROM
: