4 files changed, 12 insertions, 0 deletions
diff --git a/lib/active_storage/service/disk_service.rb b/lib/active_storage/service/disk_service.rb
index 3cde203a31..7e2079385f 100644
--- a/lib/active_storage/service/disk_service.rb
+++ b/lib/active_storage/service/disk_service.rb
@@ -3,6 +3,8 @@ require "pathname"
 require "digest/md5"
 require "active_support/core_ext/numeric/bytes"
 
+# Wraps a local disk path as a Active Storage service. See `ActiveStorage::Service` for the generic API
+# documentation that applies to all services.
 class ActiveStorage::Service::DiskService < ActiveStorage::Service
   attr_reader :root
 
diff --git a/lib/active_storage/service/gcs_service.rb b/lib/active_storage/service/gcs_service.rb
index 4632e5f820..d681a3dc45 100644
--- a/lib/active_storage/service/gcs_service.rb
+++ b/lib/active_storage/service/gcs_service.rb
@@ -1,6 +1,8 @@
 require "google/cloud/storage"
 require "active_support/core_ext/object/to_query"
 
+# Wraps the Google Cloud Storage as a Active Storage service. See `ActiveStorage::Service` for the generic API
+# documentation that applies to all services.
 class ActiveStorage::Service::GCSService < ActiveStorage::Service
   attr_reader :client, :bucket
 
diff --git a/lib/active_storage/service/mirror_service.rb b/lib/active_storage/service/mirror_service.rb
index 54465cad05..7c407f2730 100644
--- a/lib/active_storage/service/mirror_service.rb
+++ b/lib/active_storage/service/mirror_service.rb
@@ -1,5 +1,8 @@
 require "active_support/core_ext/module/delegation"
 
+# Wraps a set of mirror services and provides a single `ActiveStorage::Service` object that will all
+# have the files uploaded to them. A `primary` service is designated to answer calls to `download`, `exists?`,
+# and `url`.
 class ActiveStorage::Service::MirrorService < ActiveStorage::Service
   attr_reader :primary, :mirrors
 
@@ -16,12 +19,15 @@ class ActiveStorage::Service::MirrorService < ActiveStorage::Service
     @primary, @mirrors = primary, mirrors
   end
 
+  # Upload the `io` to the `key` specified to all services. If a `checksum` is provided, all services will
+  # ensure a match when the upload has completed or raise an `ActiveStorage::IntegrityError`.
   def upload(key, io, checksum: nil)
     each_service.collect do |service|
       service.upload key, io.tap(&:rewind), checksum: checksum
     end
   end
 
+  # Delete the file at the `key` on all services.
   def delete(key)
     perform_across_services :delete, key
   end
diff --git a/lib/active_storage/service/s3_service.rb b/lib/active_storage/service/s3_service.rb
index 72ff9f3f36..c21977044d 100644
--- a/lib/active_storage/service/s3_service.rb
+++ b/lib/active_storage/service/s3_service.rb
@@ -1,6 +1,8 @@
 require "aws-sdk"
 require "active_support/core_ext/numeric/bytes"
 
+# Wraps the Amazon Simple Storage Service (S3) as a Active Storage service.
+# See `ActiveStorage::Service` for the generic API documentation that applies to all services.
 class ActiveStorage::Service::S3Service < ActiveStorage::Service
   attr_reader :client, :bucket, :upload_options