Trim long hostnames

lib/kamal/cli/app/boot.rb

@@ -47,7 +47,8 @@ def old_version_renamed_if_clashing
     def start_new_version
       audit "Booted app version #{version}"
       execute *app.tie_cord(role.cord_host_file) if uses_cord?
-      execute *app.run(hostname: "#{host}-#{SecureRandom.hex(6)}")
+      hostname = "#{host.to_s[0...51].gsub(/\.+$/, '')}-#{SecureRandom.hex(6)}"
+      execute *app.run(hostname: hostname)
       Kamal::Cli::Healthcheck::Poller.wait_for_healthy(pause_after_ready: true) { capture_with_info(*app.status(version: version)) }
     end
 

test/cli/app_test.rb

@@ -236,6 +236,26 @@ class CliAppTest < CliTestCase
     end
   end
 
+  test "long hostname" do
+    stub_running
+
+    hostname = "this-hostname-is-really-unacceptably-long-to-be-honest.example.com"
+
+    stdouted { Kamal::Cli::App.start([ "boot", "-c", "test/fixtures/deploy_with_uncommon_hostnames.yml", "--hosts", hostname ]) }.tap do |output|
+      assert_match /docker run --detach --restart unless-stopped --name app-web-latest --hostname this-hostname-is-really-unacceptably-long-to-be-hon-[0-9a-f]{12} /, output
+    end
+  end
+
+  test "hostname is trimmed if will end with a period" do
+    stub_running
+
+    hostname = "this-hostname-with-random-part-is-too-long.example.com"
+
+    stdouted { Kamal::Cli::App.start([ "boot", "-c", "test/fixtures/deploy_with_uncommon_hostnames.yml", "--hosts", hostname ]) }.tap do |output|
+      assert_match /docker run --detach --restart unless-stopped --name app-web-latest --hostname this-hostname-with-random-part-is-too-long.example-[0-9a-f]{12} /, output
+    end
+  end
+
   private
     def run_command(*command, config: :with_accessories)
       stdouted { Kamal::Cli::App.start([ *command, "-c", "test/fixtures/deploy_#{config}.yml", "--hosts", "1.1.1.1" ]) }

test/fixtures/deploy_with_uncommon_hostnames.yml

@@ -0,0 +1,8 @@
+service: app
+image: dhh/app
+servers:
+  - "this-hostname-with-random-part-is-too-long.example.com"
+  - "this-hostname-is-really-unacceptably-long-to-be-honest.example.com"
+registry:
+  username: user
+  password: pw