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GOV.UK Ruby Images

What's in this repo

The govuk-ruby-images repository defines OCI container images for building and running production Ruby applications on Kubernetes.

  • govuk-ruby-base is a base image for production application containers; it provides:

    • a Ruby runtime that can run as an unprivileged user with a read-only filesystem
    • database client libraries
    • a Node.js runtime

  • govuk-ruby-builder is for building application container images; it provides the same as govuk-ruby-base plus:

    • a C/C++ toolchain and various build tools and utilities
    • Yarn, for building/installing Node.js package dependencies
    • configuration to speed up and optimise building Ruby applications

Usage

Use the two images in your app's Dockerfile.

Specify the image tag that corresponds to the <major>.<minor> Ruby version that your application needs.

ARG ruby_version=3.3
ARG base_image=ghcr.io/alphagov/govuk-ruby-base:$ruby_version
ARG builder_image=ghcr.io/alphagov/govuk-ruby-builder:$ruby_version

FROM $builder_image AS builder

# your build steps here

FROM $base_image

# your app image steps here

See alphagov/frontend/Dockerfile for a full, real-world example.

Supported tags

Our version maintenance policy is similar to upstream except that we drop support for a (major.minor) version series once it's no longer in use in GOV.UK.

See build-matrix.json for the list of Ruby versions we currently support.

Important

Please do not attempt to specify the Ruby patch version. See below for alternatives.

If you suspect a bug

If you encounter a bug in govuk-ruby-images that breaks your application or your build:

  • if absolutely necessary, you may temporarily pin a known-good base and/or builder image by SHA or SHA prefix, for example:

    # TODO(https://github.com/alphagov/govuk-ruby-images/issues/96): remove pinned image once bug is fixed.
ARG builder_image=ghcr.io/alphagov/govuk-ruby-builder:3.3-acecafe

  • if you pin a base/builder image SHA, you must:

    • file an issue so that the maintainers know there is a problem that needs to be addressed
    • add a TODO containing a link to the issue, so that the workaround can be cleaned up once the issue is fixed

If you are unsure, ask Platform Engineering team for advice.

Common problems and resolutions

ERROR: failed to solve: cannot copy to non-directory: /var/lib/docker/overlay2/.../merged/app/tmp

Add tmp/ to your .dockerignore. This is necessary because we symlink $APP_HOME/tmp to /tmp as a workaround for some badly-behaved gems that assume they can write to Path.join(Rails.root, 'tmp') so that we can run with readOnlyRootFilesystem.

Maintenance

Add or update a Ruby version

The file build-matrix.json defines the Ruby versions and image tags that we build.

The checksum field is currently the SHA-256 hash of the Ruby source tarball. We verify this in the build.

See Ruby Releases for the list of available Ruby tarballs and their SHA digests.

Team

GOV.UK Platform Engineering team looks after this repo. If you're inside GDS, you can find us in #govuk-platform-engineering or view our project board.