Dockerfile when using ARG in FROM doesn't work

[bilby91]

I was testing the project using this devcontainer specification and envbuilder is failing to build the following Dockerfile => https://github.com/crunchloop/rails-interview/blob/main/.devcontainer/Dockerfile#L3

It throws and error indicating that it can't parse the image. This is working fine with devcontainer cli. I'm going to post the error soon since I don't have it with me.

Removing the VARIANT and hard coding the value made it work.

[bilby91]

Got some time to capture the error:

2023-07-18T20:22:02.964 app[91857917c5d783] eze [info] error: compile devcontainer.json: parse image from dockerfile: parse image ref "mcr.microsoft.com/devcontainers/ruby:${VARIANT}": could not parse reference: mcr.microsoft.com/devcontainers/ruby:${VARIANT}

[kylecarbs]

Ahh, will fix this!

[bilby91]

@kylecarbs Confirmed that this is working now!

[kylecarbs]

Fantastic!