From ff7a1e6726d50fe263dc933c016c3d23fc273ee7 Mon Sep 17 00:00:00 2001
From: Donal McBreen <donal@basecamp.com>
Date: Thu, 25 May 2023 16:32:54 +0100
Subject: [PATCH] Prune unused images correctly

dangling=true doesn't prune any images, as we are not creating dangling
images.

Using --all should remove unused images, but it considers the Git SHA
tag on the latest image to be unused (presumably because there are two
tags, the SHA and latest and the running container is only considered to
be using "latest"). As a result it deletes the tag, which means that we
can't rollback to that SHA later.

Its a bit more complicated to only remove images that are not referenced
by any containers.

First we find the tags we want to keep from the containers (running and
stopped).

Then we append the latest tag to that list.

Then we get a full list of image tags and remove those tags from that
list (using `grep -v -w`).

Finally we pass the tags to `docker rmi`. That either deletes the tag if
there are other references to the image or both the tag and the image if
it is the only one.
---
 lib/mrsk/commands/prune.rb  | 15 +++++++++++++--
 test/cli/prune_test.rb      |  2 +-
 test/commands/prune_test.rb |  2 +-
 3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/lib/mrsk/commands/prune.rb b/lib/mrsk/commands/prune.rb
index 79da58be..3b68fe3f 100644
--- a/lib/mrsk/commands/prune.rb
+++ b/lib/mrsk/commands/prune.rb
@@ -3,12 +3,15 @@ require "active_support/core_ext/numeric/time"
 
 class Mrsk::Commands::Prune < Mrsk::Commands::Base
   def images
-    docker :image, :prune, "--force", "--filter", "label=service=#{config.service}", "--filter", "dangling=true"
+    pipe \
+      docker(:image, :ls, *service_filter, "--format", "'{{.Repository}}:{{.Tag}}'"),
+      "grep -v -w \"#{active_image_list}\"",
+      "while read tag; do docker rmi $tag; done"
   end
 
   def containers(keep_last: 5)
     pipe \
-      docker(:ps, "-q", "-a", "--filter", "label=service=#{config.service}", *stopped_containers_filters),
+      docker(:ps, "-q", "-a", *service_filter, *stopped_containers_filters),
       "tail -n +#{keep_last + 1}",
       "while read container_id; do docker rm $container_id; done"
   end
@@ -17,4 +20,12 @@ class Mrsk::Commands::Prune < Mrsk::Commands::Base
     def stopped_containers_filters
       [ "created", "exited", "dead" ].flat_map { |status| ["--filter", "status=#{status}"] }
     end
+
+    def active_image_list
+      "$(docker container ls -a --format '{{.Image}}\\|' --filter label=service=#{config.service} | tr -d '\\n')#{config.latest_image}"
+    end
+
+    def service_filter
+      [ "--filter", "label=service=#{config.service}" ]
+    end
 end
diff --git a/test/cli/prune_test.rb b/test/cli/prune_test.rb
index e07f3172..85cdf159 100644
--- a/test/cli/prune_test.rb
+++ b/test/cli/prune_test.rb
@@ -10,7 +10,7 @@ class CliPruneTest < CliTestCase
 
   test "images" do
     run_command("images").tap do |output|
-      assert_match /docker image prune --force --filter label=service=app --filter dangling=true on 1.1.1.\d/, output
+      assert_match "docker image ls --filter label=service=app --format '{{.Repository}}:{{.Tag}}' | grep -v -w \"$(docker container ls -a --format '{{.Image}}\\|' --filter label=service=app | tr -d '\\n')dhh/app:latest\" | while read tag; do docker rmi $tag; done on 1.1.1.", output
     end
   end
 
diff --git a/test/commands/prune_test.rb b/test/commands/prune_test.rb
index 436ed02f..f4025893 100644
--- a/test/commands/prune_test.rb
+++ b/test/commands/prune_test.rb
@@ -10,7 +10,7 @@ class CommandsPruneTest < ActiveSupport::TestCase
 
   test "images" do
     assert_equal \
-      "docker image prune --force --filter label=service=app --filter dangling=true",
+      "docker image ls --filter label=service=app --format '{{.Repository}}:{{.Tag}}' | grep -v -w \"$(docker container ls -a --format '{{.Image}}\\|' --filter label=service=app | tr -d '\\n')dhh/app:latest\" | while read tag; do docker rmi $tag; done",
       new_command.images.join(" ")
   end