1 files changed, 62 insertions, 0 deletions
diff --git a/lib/gitlab/ci/runner_upgrade_check.rb b/lib/gitlab/ci/runner_upgrade_check.rb
new file mode 100644
index 00000000000..baf041fc358
--- /dev/null
+++ b/lib/gitlab/ci/runner_upgrade_check.rb
@@ -0,0 +1,62 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Ci
+    class RunnerUpgradeCheck
+      include Singleton
+
+      def initialize
+        reset!
+      end
+
+      def check_runner_upgrade_status(runner_version)
+        return :unknown unless runner_version
+
+        releases = RunnerReleases.instance.releases
+        parsed_runner_version = runner_version.is_a?(::Gitlab::VersionInfo) ? runner_version : ::Gitlab::VersionInfo.parse(runner_version)
+
+        raise ArgumentError, "'#{runner_version}' is not a valid version" unless parsed_runner_version.valid?
+
+        available_releases = releases.reject { |release| release > @gitlab_version }
+
+        return :recommended if available_releases.any? { |available_release| patch_update?(available_release, parsed_runner_version) }
+        return :recommended if outside_backport_window?(parsed_runner_version, releases)
+        return :available if available_releases.any? { |available_release| available_release > parsed_runner_version }
+
+        :not_available
+      end
+
+      def reset!
+        @gitlab_version = ::Gitlab::VersionInfo.parse(::Gitlab::VERSION)
+      end
+
+      public_class_method :instance
+
+      private
+
+      def patch_update?(available_release, runner_version)
+        # https://docs.gitlab.com/ee/policy/maintenance.html#patch-releases
+        available_release.major == runner_version.major &&
+          available_release.minor == runner_version.minor &&
+          available_release.patch > runner_version.patch
+      end
+
+      def outside_backport_window?(runner_version, releases)
+        return false if runner_version >= releases.last # return early if runner version is too new
+
+        latest_minor_releases = releases.map { |r| version_without_patch(r) }.uniq { |v| v.to_s }
+        latest_version_position = latest_minor_releases.count - 1
+        runner_version_position = latest_minor_releases.index(version_without_patch(runner_version))
+
+        return true if runner_version_position.nil? # consider outside if version is too old
+
+        # https://docs.gitlab.com/ee/policy/maintenance.html#backporting-to-older-releases
+        latest_version_position - runner_version_position > 2
+      end
+
+      def version_without_patch(version)
+        ::Gitlab::VersionInfo.new(version.major, version.minor, 0)
+      end
+    end
+  end
+end