Merge branch 'mailroom-arbitration' into 'master'

Enable arbitration in MailRoom

Fixes #2870.

See merge request !1566

Gemfile

@@ -290,7 +290,7 @@ gem 'newrelic-grape'
 gem 'octokit', '~> 3.7.0'
-gem "mail_room", "~> 0.5.2"
+gem "mail_room", "~> 0.6.0"
 gem 'email_reply_parser', '~> 0.5.8'

Gemfile.lock

@@ -392,7 +392,7 @@ GEM
       systemu (~> 2.6.2)
     mail (2.6.3)
       mime-types (>= 1.16, < 3)
-    mail_room (0.5.2)
+    mail_room (0.6.0)
     method_source (0.8.2)
     mime-types (1.25.1)
     mimemagic (0.3.0)
@@ -854,7 +854,7 @@ DEPENDENCIES
   jquery-ui-rails (~> 4.2.1)
   kaminari (~> 0.16.3)
   letter_opener (~> 1.1.2)
-  mail_room (~> 0.5.2)
+  mail_room (~> 0.6.0)
   minitest (~> 5.7.0)
   mousetrap-rails (~> 1.4.6)
   mysql2 (~> 0.3.16)

config/mail_room.yml.example

@@ -12,8 +12,10 @@
     # :email: "gitlab-incoming@gmail.com"
     # # Email account password
     # :password: "password"
+
     # # The name of the mailbox where incoming mail will end up. Usually "inbox".
     # :name: "inbox"
+
     # # Always "sidekiq".
     # :delivery_method: sidekiq
     # # Always true.
@@ -25,5 +27,13 @@
     #   :namespace: resque:gitlab
     #   # Always "incoming_email".
     #   :queue: incoming_email
-    #   # Always "EmailReceiverWorker"
+    #   # Always "EmailReceiverWorker".
     #   :worker: EmailReceiverWorker
+
+    # # Always "redis".
+    # :arbitration_method: redis
+    # :arbitration_options:
+    #   # The URL to the Redis server. Should match the URL in config/resque.yml.
+    #   :redis_url: redis://localhost:6379
+    #   # Always "mail_room:gitlab".
+    #   :namespace: mail_room:gitlab

doc/incoming_email/README.md

@@ -2,10 +2,6 @@
 GitLab can be set up to allow users to comment on issues and merge requests by replying to notification emails.
-**Warning**: Do not enable Reply by email if you have **multiple GitLab application servers**. 
-Due to an issue with the way incoming emails are read from the mail server, every incoming reply-by-email email will result in as many comments being created as you have application servers.
-[A fix is being worked on.](https://github.com/tpitale/mail_room/issues/46)
-
 ## Get a mailbox
 Reply by email requires an IMAP-enabled email account, with a provider or server that supports [email sub-addressing](https://en.wikipedia.org/wiki/Email_address#Sub-addressing). Sub-addressing is a feature where any email to `user+some_arbitrary_tag@example.com` will end up in the mailbox for `user@example.com`, and is supported by providers such as Gmail, Yahoo! Mail, Outlook.com and iCloud, as well as the Postfix mail server which you can run on-premises.
@@ -118,8 +114,10 @@ To set up a basic Postfix mail server with IMAP access on Ubuntu, follow [these
         :email: "incoming"
         # Email account password
         :password: "[REDACTED]"
+
         # The name of the mailbox where incoming mail will end up. Usually "inbox".
         :name: "inbox"
+
         # Always "sidekiq".
         :delivery_method: sidekiq
         # Always true.
@@ -133,6 +131,14 @@ To set up a basic Postfix mail server with IMAP access on Ubuntu, follow [these
           :queue: incoming_email
           # Always "EmailReceiverWorker"
           :worker: EmailReceiverWorker
+
+        # Always "redis".
+        :arbitration_method: redis
+        :arbitration_options:
+          # The URL to the Redis server. Should match the URL in config/resque.yml.
+          :redis_url: redis://localhost:6379
+          # Always "mail_room:gitlab".
+          :namespace: mail_room:gitlab
     ```
     ```yaml
@@ -151,8 +157,10 @@ To set up a basic Postfix mail server with IMAP access on Ubuntu, follow [these
         :email: "gitlab-incoming@gmail.com"
         # Email account password
         :password: "[REDACTED]"
+
         # The name of the mailbox where incoming mail will end up. Usually "inbox".
         :name: "inbox"
+
         # Always "sidekiq".
         :delivery_method: sidekiq
         # Always true.
@@ -166,6 +174,14 @@ To set up a basic Postfix mail server with IMAP access on Ubuntu, follow [these
           :queue: incoming_email
           # Always "EmailReceiverWorker"
           :worker: EmailReceiverWorker
+
+        # Always "redis".
+        :arbitration_method: redis
+        :arbitration_options:
+          # The URL to the Redis server. Should match the URL in config/resque.yml.
+          :redis_url: redis://localhost:6379
+          # Always "mail_room:gitlab".
+          :namespace: mail_room:gitlab
     ```
 5. Edit the init script configuration at `/etc/default/gitlab` to enable `mail_room`:
@@ -228,8 +244,10 @@ To set up a basic Postfix mail server with IMAP access on Ubuntu, follow [these
         :email: "gitlab-incoming@gmail.com"
         # Email account password
         :password: "[REDACTED]"
+
         # The name of the mailbox where incoming mail will end up. Usually "inbox".
         :name: "inbox"
+
         # Always "sidekiq".
         :delivery_method: sidekiq
         # Always true.
@@ -243,6 +261,14 @@ To set up a basic Postfix mail server with IMAP access on Ubuntu, follow [these
           :queue: incoming_email
           # Always "EmailReceiverWorker"
           :worker: EmailReceiverWorker
+
+        # Always "redis".
+        :arbitration_method: redis
+        :arbitration_options:
+          # The URL to the Redis server. Should match the URL in config/resque.yml.
+          :redis_url: redis://localhost:6379
+          # Always "mail_room:gitlab".
+          :namespace: mail_room:gitlab
     ```
 4. Uncomment the `mail_room` line in your `Procfile`: