Enhance rollback to attempt to find a version when one is not specified

lib/kamal/cli/main.rb

@@ -80,22 +80,30 @@ def redeploy
   end
 
   desc "rollback [VERSION]", "Rollback app to VERSION"
-  def rollback(version)
+  def rollback(version = nil)
     rolled_back = false
     runtime = print_runtime do
       with_lock do
         invoke_options = deploy_options
 
-        KAMAL.config.version = version
-        old_version = nil
+        if version.to_s.strip.empty?
+          version = previous_container_version
+          unless version.present?
+            say "No previous version is available on all hosts — aborting automated rollback. Run `kamal app containers` to list available versions.", :red
+          end
+        end
 
-        if container_available?(version)
-          run_hook "pre-deploy", secrets: true
+        if version.present?
+          KAMAL.config.version = version
 
-          invoke "kamal:cli:app:boot", [], invoke_options.merge(version: version)
-          rolled_back = true
-        else
-          say "The app version '#{version}' is not available as a container (use 'kamal app containers' for available versions)", :red
+          if container_available?(version)
+            run_hook "pre-deploy", secrets: true
+
+            invoke "kamal:cli:app:boot", [], invoke_options.merge(version: version)
+            rolled_back = true
+          else
+            say "The app version '#{version}' is not available as a container (use 'kamal app containers' for available versions)", :red
+          end
         end
       end
     end
@@ -279,4 +287,34 @@ def deploy_options
       base_options = base_options.except("no_cache") unless base_options["no_cache"]
       { "version" => KAMAL.config.version }.merge(base_options)
     end
+
+    def previous_container_version
+      versions_per_host_and_role = []
+
+      on(KAMAL.app_hosts) do |host|
+        KAMAL.roles_on(host).each do |role|
+          app = KAMAL.app(role: role, host: host)
+
+          versions_raw = capture_with_info(*app.list_versions("--all"), raise_on_non_zero_exit: false).to_s
+          versions = versions_raw.split("\n").map(&:strip).reject(&:empty?)
+
+          current_raw = capture_with_info(*app.current_running_version, raise_on_non_zero_exit: false).to_s
+          current = current_raw.strip
+
+          rollback_versions = versions - [ current ]
+          versions_per_host_and_role << rollback_versions
+        end
+      end
+
+      return nil if versions_per_host_and_role.empty?
+
+      intersection = versions_per_host_and_role.reduce { |a, b| a & b } || []
+      return nil if intersection.empty?
+
+      ordered_versions = versions_per_host_and_role.flatten.uniq
+      version = ordered_versions.find { |v| intersection.include?(v) }
+      version.presence
+    rescue SSHKit::Runner::ExecuteError, SSHKit::Runner::MultipleExecuteError
+      raise
+    end
 end

test/cli/main_test.rb

@@ -377,6 +377,51 @@ class CliMainTest < CliTestCase
     end
   end
 
+    test "rollback uses previous_container_version when no version supplied" do
+    Object.any_instance.stubs(:sleep)
+
+    Kamal::Cli::Main.any_instance.stubs(:previous_container_version).returns("123")
+
+    [ "web", "workers" ].each do |role|
+      SSHKit::Backend::Abstract.any_instance.expects(:capture_with_info)
+        .with(:docker, :container, :ls, "--all", "--filter", "name=^app-#{role}-123$", "--quiet", raise_on_non_zero_exit: false)
+        .returns("").at_least_once
+      SSHKit::Backend::Abstract.any_instance.expects(:capture_with_info)
+        .with(:docker, :container, :ls, "--all", "--filter", "name=^app-#{role}-123$", "--quiet")
+        .returns("version-to-rollback\n").at_least_once
+      SSHKit::Backend::Abstract.any_instance.expects(:capture_with_info)
+        .with(:sh, "-c", "'docker ps --latest --format '\\''{{.Names}}'\\'' --filter label=service=app --filter label=destination= --filter label=role=#{role} --filter status=running --filter status=restarting --filter ancestor=$(docker image ls --filter reference=dhh/app:latest --format '\\''{{.ID}}'\\'') ; docker ps --latest --format '\\''{{.Names}}'\\'' --filter label=service=app --filter label=destination= --filter label=role=#{role} --filter status=running --filter status=restarting'", "|", :head, "-1", "|", "while read line; do echo ${line#app-#{role}-}; done", raise_on_non_zero_exit: false)
+        .returns("version-to-rollback\n").at_least_once
+    end
+
+    SSHKit::Backend::Abstract.any_instance.expects(:capture_with_info)
+      .with(:docker, :container, :ls, "--all", "--filter", "name=^app-workers-123$", "--quiet", "|", :xargs, :docker, :inspect, "--format", "'{{if .State.Health}}{{.State.Health.Status}}{{else}}{{.State.Status}}{{end}}'")
+      .returns("running").at_least_once
+
+    Kamal::Commands::Hook.any_instance.stubs(:hook_exists?).returns(true)
+
+    run_command("rollback", "--verbose", config_file: "deploy_with_accessories").tap do |output|
+      assert_hook_ran "pre-deploy", output
+      assert_match "docker tag dhh/app:123 dhh/app:latest", output
+      assert_match "docker run --detach --restart unless-stopped --name app-web-123", output
+      assert_match "docker container ls --all --filter name=^app-web-version-to-rollback$ --quiet | xargs docker stop", output, "Should stop the container that was previously running"
+      assert_hook_ran "post-deploy", output
+    end
+  end
+
+  test "rollback prints helpful message and returns when previous_container_version not found" do
+    Thread.report_on_exception = false
+
+    Kamal::Cli::Main.any_instance.stubs(:previous_container_version).returns(nil)
+
+    output = run_command("rollback", "--verbose")
+
+    assert_match /No previous version is available on all hosts\s*—\s*aborting automated rollback\./i, output
+    assert_match /kamal app containers/, output, "Message should suggest `kamal app containers`"
+    assert_no_match /docker run --detach --restart unless-stopped/, output
+  end
+
+
   test "remove" do
     options = { "config_file" => "test/fixtures/deploy_simple.yml", "skip_hooks" => false, "confirmed" => true }
     Kamal::Cli::Main.any_instance.expects(:invoke).with("kamal:cli:proxy:remove", [], options)