Zero downtime deployment with cord file

When replacing a container currently we:
1. Boot the new container
2. Wait for it to become healthy
3. Stop the old container

Traefik will send requests to the old container until it notices that it
is unhealthy. But it may have stopped serving requests before that point
which can result in errors.

To get round that the new boot process is:

1. Create a directory with a single file on the host
2. Boot the new container, mounting the cord file into /tmp and
including a check for the file in the docker healthcheck
3. Wait for it to become healthy
4. Delete the healthcheck file ("cut the cord") for the old container
5. Wait for it to become unhealthy and give Traefik a couple of seconds
to notice
6. Stop the old container

The extra steps ensure that Traefik stops sending requests before the
old container is shutdown.

test/cli/main_test.rb

@@ -176,9 +176,10 @@ class CliMainTest < CliTestCase
   end
 
   test "rollback good version" do
+    Object.any_instance.stubs(:sleep)
     [ "web", "workers" ].each do |role|
       SSHKit::Backend::Abstract.any_instance.expects(:capture_with_info)
-        .with(:docker, :container, :ls, "--filter", "name=^app-#{role}-123$", "--quiet", raise_on_non_zero_exit: false)
+        .with(:docker, :container, :ls, "--all", "--filter", "name=^app-#{role}-123$", "--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")
@@ -191,14 +192,21 @@ class CliMainTest < CliTestCase
         .returns("running").at_least_once # health check
     end
 
+    SSHKit::Backend::Abstract.any_instance.expects(:capture_with_info)
+      .with(:docker, :inspect, "-f '{{ range .Mounts }}{{ .Source }} {{ .Destination }} {{ end }}'", "app-web-version-to-rollback", "|", :awk, "'$2 == \"/tmp/kamal-cord\" {print $1}'", :raise_on_non_zero_exit => false)
+      .returns("corddirectory").at_least_once # health check
+
+    SSHKit::Backend::Abstract.any_instance.expects(:capture_with_info)
+      .with(:docker, :container, :ls, "--all", "--filter", "name=^app-web-version-to-rollback$", "--quiet", "|", :xargs, :docker, :inspect, "--format", "'{{if .State.Health}}{{.State.Health.Status}}{{else}}{{.State.Status}}{{end}}'")
+      .returns("unhealthy").at_least_once # health check
+
     Kamal::Commands::Hook.any_instance.stubs(:hook_exists?).returns(true)
     hook_variables = { version: 123, service_version: "app@123", hosts: "1.1.1.1,1.1.1.2,1.1.1.3,1.1.1.4", command: "rollback" }
 
     run_command("rollback", "123", config_file: "deploy_with_accessories").tap do |output|
-      assert_match "Start container with version 123", output
       assert_hook_ran "pre-deploy", output, **hook_variables
       assert_match "docker tag dhh/app:123 dhh/app:latest", output
-      assert_match "docker start app-web-123", 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, **hook_variables, runtime: "0"
     end
@@ -210,7 +218,7 @@ class CliMainTest < CliTestCase
     Kamal::Utils::HealthcheckPoller.stubs(:sleep)
 
     SSHKit::Backend::Abstract.any_instance.expects(:capture_with_info)
-      .with(:docker, :container, :ls, "--filter", "name=^app-web-123$", "--quiet", raise_on_non_zero_exit: false)
+      .with(:docker, :container, :ls, "--all", "--filter", "name=^app-web-123$", "--quiet", raise_on_non_zero_exit: false)
       .returns("").at_least_once
     SSHKit::Backend::Abstract.any_instance.expects(:capture_with_info)
       .with(:docker, :ps, "--filter", "label=service=app", "--filter", "label=role=web", "--filter", "status=running", "--filter", "status=restarting", "--latest", "--format", "\"{{.Names}}\"", "|", "while read line; do echo ${line#app-web-}; done", raise_on_non_zero_exit: false)
@@ -220,8 +228,7 @@ class CliMainTest < CliTestCase
       .returns("running").at_least_once # health check
 
     run_command("rollback", "123").tap do |output|
-      assert_match "Start container with version 123", output
-      assert_match "docker start app-web-123 || docker run --detach --restart unless-stopped --name app-web-123", output
+      assert_match "docker run --detach --restart unless-stopped --name app-web-123", output
       assert_no_match "docker stop", output
     end
   end