Push an immutable tag on release

Push an immutable tag on release

This commit will allow old mobystash container images to linger on Docker Hub after a new release.

Docker Hub

In turn, this will allow users to pin to a specific image hash (and be confident that it will not disappear unexpectedly), and roll back to an earlier mobystash release in the event of a regression. The mutable :latest tag behaves as it did before.

This version number is the simplest thing that could possibly work. It is syntactically compliant with semver.org, though these version numbers are not chronologically or semantically comparable. For now, we only require a unique ref per release. If necessary, semantics may be trivially introduced in the future by bumping the MINOR version.

diff --git a/Rakefile b/Rakefile
index ca464b3..263c5be 100644
--- a/Rakefile
+++ b/Rakefile
@@ -12,6 +12,21 @@ rescue Bundler::BundlerError => e
   exit e.status_code
+def git_describe
+  @git_describe ||= `git describe --always --dirty`.chomp
+def version
+  build_metadata = git_describe()
+  raise RuntimeError.new("Received empty build metadata from 'git describe'") unless build_metadata.length > 0
+  "0.0.1-git+#{build_metadata}"
+def docker_tagify(tag)
+  # https://docs.docker.com/engine/reference/commandline/tag/
+  tag.tr_s('^A-Za-z0-9_.\-', '-').sub(/^-+/, '')
 require 'yard'
 task :rubocop do
@@ -37,14 +52,18 @@ RSpec::Core::RakeTask.new :test do |t|
 namespace :docker do
+  tag = docker_tagify(version())
   desc "Build a new docker image"
   task :build do
     sh "docker pull ruby:2.3-alpine"
     sh "docker build -t discourse/mobystash --build-arg=http_proxy=#{ENV['http_proxy']} --build-arg=GIT_REVISION=$(git rev-parse HEAD) ."
+    sh "docker tag discourse/mobystash discourse/mobystash:#{tag}"
   desc "Publish a new docker image"
   task publish: :build do
+    sh "docker push discourse/mobystash:#{tag}"
     sh "docker push discourse/mobystash"

GitHub sha: c3191695