Queue the builds CDN purge instead of sleeping in the request

lib/bob/artifacts.ex

@@ -21,11 +21,12 @@ defmodule Bob.Artifacts do
   @erlang_arch_repos ~w(hexpm/erlang-amd64 hexpm/erlang-arm64)
   @docker_cleanup_per_arch_repos ~w(hexpm/elixir-amd64 hexpm/elixir-arm64) ++ @erlang_arch_repos
 
+  # The CDN purge sleeps 4 seconds between each of its three requests, so it is
+  # queued rather than run in the agent's POST /api/artifacts/add.
   def add(attrs) do
     upsert(attrs)
     generate_builds_txt(attrs.arch, attrs.os)
-    Bob.Fastly.purge_builds(purge_keys(attrs.arch, attrs.os, attrs.name))
-    :ok
+    Bob.Queue.add(Bob.Job.PurgeBuilds, [purge_keys(attrs.arch, attrs.os, attrs.name)])
   end
 
   def add_docker_tag(repo, tag, archs, built_at \\ DateTime.utc_now()) do

lib/bob/job/purge_builds.ex

@@ -0,0 +1,9 @@
+defmodule Bob.Job.PurgeBuilds do
+  def run(keys) do
+    Bob.Fastly.purge_builds(keys)
+  end
+
+  def priority(), do: 1
+  def weight(), do: 1
+  def concurrency(), do: :shared
+end

lib/bob/queue.ex

@@ -10,12 +10,16 @@ defmodule Bob.Queue do
 
   # Periodic scheduler jobs re-run every interval and must not be suppressed by
   # backoff after a transient failure; only the build jobs they enqueue back off.
+  # A builds purge is queued once per uploaded artifact and nothing re-queues it,
+  # so backing off after a failed purge would skip the next build's purge of the
+  # same keys.
   @no_backoff [
     Bob.Job.OTPChecker,
     Bob.Job.DockerChecker,
     Bob.Job.Reconcile,
     Bob.Job.ReconcileBaseImages,
-    Bob.Job.DockerCleanup
+    Bob.Job.DockerCleanup,
+    Bob.Job.PurgeBuilds
   ]
 
   @dedup_conflict_target {:unsafe_fragment,

test/bob/artifacts_test.exs

@@ -163,7 +163,7 @@ defmodule Bob.ArtifactsTest do
   end
 
   describe "add/1" do
-    test "upserts and regenerates builds.txt" do
+    test "upserts, regenerates builds.txt and queues the CDN purge" do
       Bob.FakeHttpClient.reset()
 
       Bob.FakeHttpClient.stub(
@@ -175,6 +175,13 @@ defmodule Bob.ArtifactsTest do
 
       assert Artifacts.add(attrs()) == :ok
       assert [%Artifact{name: "OTP-27.0"}] = Repo.all(Artifact)
+
+      assert Bob.Queue.queued() == [
+               {Bob.Job.PurgeBuilds,
+                [
+                  "builds/otp/amd64/ubuntu-24.04/txt builds/otp/amd64/ubuntu-24.04/OTP-27.0"
+                ]}
+             ]
     end
   end
 

test/bob/job/purge_builds_test.exs

@@ -0,0 +1,18 @@
+defmodule Bob.Job.PurgeBuildsTest do
+  use ExUnit.Case
+
+  alias Bob.Job.PurgeBuilds
+
+  test "exposes the runner callbacks" do
+    assert PurgeBuilds.priority() == 1
+    assert PurgeBuilds.weight() == 1
+    assert PurgeBuilds.concurrency() == :shared
+  end
+
+  test "run/1 purges the keys, a no-op when Fastly is not configured" do
+    System.delete_env("BOB_FASTLY_KEY")
+    System.delete_env("BOB_FASTLY_SERVICE_BUILDS")
+
+    assert PurgeBuilds.run("builds/otp/amd64/ubuntu-24.04/txt") == :ok
+  end
+end

test/bob/queue_test.exs

@@ -154,6 +154,17 @@ defmodule Bob.QueueTest do
     end
   end
 
+  test "a failed builds purge does not back off the next purge of the same keys" do
+    keys = "builds/otp/amd64/ubuntu-24.04/txt builds/otp/amd64/ubuntu-24.04/master"
+
+    Queue.add(Bob.Job.PurgeBuilds, [keys])
+    {:ok, {id, [^keys]}} = Queue.start(Bob.Job.PurgeBuilds)
+    Queue.failure(id)
+    Queue.add(Bob.Job.PurgeBuilds, [keys])
+
+    assert size(Bob.Job.PurgeBuilds) == 1
+  end
+
   test "success clears any existing backoff for the job" do
     # Set up a previously-failed job that is now running again, by inserting
     # the rows directly (a backed-off job will not re-enter the queue on its own).