Asset paths

During deployments both the old and new containers will be active for a
small period of time. There also may be lagging requests for older CSS
and JS after the deployment.

This can lead to 404s if a request for old assets hits a new container
or visa-versa.

This PR makes sure that both sets of assets are available throughout the
deployment from before the new version of the app is booted.

This can be configured by setting the asset path:

```yaml
asset_path: "/rails/public/assets"
```

The process is:
1. We extract the assets out of the container, with docker run, docker
cp, docker stop. Docker run sets the container command to "sleep" so
this needs to be available in the container.
2. We create an asset volume directory on the host for the new version
of the app on the host and copy the assets in there.
3. If there is a previous deployment we also copy the new assets into
its asset volume and copy the older assets into the new asset volume.
4. We start the new container mapping the asset volume over the top of
the container's asset path.

This means the both the old and new versions have replaced the asset
path with a volume containing both sets of assets and should be able
to serve any request during the deployment. The older assets will
continue to be available until the next deployment.

test/configuration/role_test.rb

@@ -80,6 +80,15 @@ class ConfigurationRoleTest < ActiveSupport::TestCase
     assert_equal expected_env, @config_with_roles.role(:workers).env_file
   end
 
+  test "container name" do
+    ENV["VERSION"] = "12345"
+
+    assert_equal "app-workers-12345", @config_with_roles.role(:workers).container_name
+    assert_equal "app-web-12345", @config_with_roles.role(:web).container_name
+  ensure
+    ENV.delete("VERSION")
+  end
+
   test "env args" do
     assert_equal ["--env-file", ".kamal/env/roles/app-workers.env"], @config_with_roles.role(:workers).env_args
   end
@@ -180,19 +189,67 @@ class ConfigurationRoleTest < ActiveSupport::TestCase
     assert !@config_with_roles.role(:workers).uses_cord?
   end
 
-  test "cord host directory" do
-    assert_match %r{\$\(pwd\)/.kamal/cords/app-web-[0-9a-f]{32}}, @config_with_roles.role(:web).cord_host_directory
-  end
-
   test "cord host file" do
-    assert_match %r{\$\(pwd\)/.kamal/cords/app-web-[0-9a-f]{32}/cord}, @config_with_roles.role(:web).cord_host_file
+    assert_match %r{.kamal/cords/app-web-[0-9a-f]{32}/cord}, @config_with_roles.role(:web).cord_host_file
   end
 
-  test "cord container directory" do
-    assert_equal "/tmp/kamal-cord", @config_with_roles.role(:web).cord_container_directory
+  test "cord volume" do
+    assert_equal "/tmp/kamal-cord", @config_with_roles.role(:web).cord_volume.container_path
+    assert_match %r{.kamal/cords/app-web-[0-9a-f]{32}}, @config_with_roles.role(:web).cord_volume.host_path
+    assert_equal "--volume", @config_with_roles.role(:web).cord_volume.docker_args[0]
+    assert_match %r{\$\(pwd\)/.kamal/cords/app-web-[0-9a-f]{32}:/tmp/kamal-cord}, @config_with_roles.role(:web).cord_volume.docker_args[1]
   end
 
   test "cord container file" do
     assert_equal "/tmp/kamal-cord/cord", @config_with_roles.role(:web).cord_container_file
   end
+
+  test "asset path and volume args" do
+    ENV["VERSION"] = "12345"
+    assert_nil @config_with_roles.role(:web).asset_volume_args
+    assert_nil @config_with_roles.role(:workers).asset_volume_args
+    assert_nil @config_with_roles.role(:web).asset_path
+    assert_nil @config_with_roles.role(:workers).asset_path
+    assert !@config_with_roles.role(:web).assets?
+    assert !@config_with_roles.role(:workers).assets?
+
+    config_with_assets = Kamal::Configuration.new(@deploy_with_roles.dup.tap { |c|
+      c[:asset_path] = "foo"
+    })
+    assert_equal "foo", config_with_assets.role(:web).asset_path
+    assert_equal "foo", config_with_assets.role(:workers).asset_path
+    assert_equal ["--volume", "$(pwd)/.kamal/assets/volumes/app-web-12345:foo"], config_with_assets.role(:web).asset_volume_args
+    assert_nil config_with_assets.role(:workers).asset_volume_args
+    assert config_with_assets.role(:web).assets?
+    assert !config_with_assets.role(:workers).assets?
+
+    config_with_assets = Kamal::Configuration.new(@deploy_with_roles.dup.tap { |c|
+      c[:servers]["web"] = { "hosts" => [ "1.1.1.1", "1.1.1.2" ], "asset_path" => "bar" }
+    })
+    assert_equal "bar", config_with_assets.role(:web).asset_path
+    assert_nil config_with_assets.role(:workers).asset_path
+    assert_equal ["--volume", "$(pwd)/.kamal/assets/volumes/app-web-12345:bar"], config_with_assets.role(:web).asset_volume_args
+    assert_nil config_with_assets.role(:workers).asset_volume_args
+    assert config_with_assets.role(:web).assets?
+    assert !config_with_assets.role(:workers).assets?
+
+  ensure
+    ENV.delete("VERSION")
+  end
+
+  test "asset extracted path" do
+    ENV["VERSION"] = "12345"
+    assert_equal ".kamal/assets/extracted/app-web-12345", @config_with_roles.role(:web).asset_extracted_path
+    assert_equal ".kamal/assets/extracted/app-workers-12345", @config_with_roles.role(:workers).asset_extracted_path
+  ensure
+    ENV.delete("VERSION")
+  end
+
+  test "asset volume path" do
+    ENV["VERSION"] = "12345"
+    assert_equal ".kamal/assets/volumes/app-web-12345", @config_with_roles.role(:web).asset_volume_path
+    assert_equal ".kamal/assets/volumes/app-workers-12345", @config_with_roles.role(:workers).asset_volume_path
+  ensure
+    ENV.delete("VERSION")
+  end
 end

test/configuration/volume_test.rb

@@ -0,0 +1,13 @@
+require "test_helper"
+
+class ConfigurationVolumeTest < ActiveSupport::TestCase
+  test "docker args absolute" do
+    volume = Kamal::Configuration::Volume.new(host_path: "/root/foo/bar", container_path: "/assets")
+    assert_equal ["--volume", "/root/foo/bar:/assets"], volume.docker_args
+  end
+
+  test "docker args relative" do
+    volume = Kamal::Configuration::Volume.new(host_path: "foo/bar", container_path: "/assets")
+    assert_equal ["--volume", "$(pwd)/foo/bar:/assets"], volume.docker_args
+  end
+end