Shortfix: When updating Dockerfile to use ruby3.0.3-alpine pin alpine to alpine3.13

If you update your Dockerfile to use ruby:3.0.3-alpine and notice the following error while building the image:

ERROR:  While executing gem ... (Gem::FilePermissionError)
    You don't have write permissions for the /usr/local/bundle directory.

First know that 3.0.3-alpine actually is using alpine3.14.

The fix is to pin the alpine version to 3.13 so use in your Dockerfile:

FROM ruby:3.0.3-alpine3.13

Why this happens:

Seems like something changed in alpine3.14 and bundle cannot write in /usr/local/bundle.

Multiple people had this issue:

• Gitlab https://gitlab.com/gitlab-org/gitlab/-/issues/335641
• Ruby Official Docker Library: https://github.com/docker-library/ruby/issues/354

It seems to be related to Docker Version running the Dockerfile:

• https://github.com/docker-library/ruby/issues/351