Merge branch 'gitlab_architecture' into 'master'

Refactor GitLab architecture document

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/14236

See merge request !3694

doc/development/architecture.md

@@ -52,7 +52,9 @@ To serve repositories over SSH there's an add-on application called gitlab-shell
 
 ### Components
 
-![GitLab Diagram Overview](gitlab_diagram_overview.png)
+![GitLab Diagram Overview](gitlab_architecture_diagram.png)
+ 
+_[edit diagram (for GitLab team members only)](https://docs.google.com/drawings/d/1fBzAyklyveF-i-2q-OHUIqDkYfjjxC4mq5shwKSZHLs/edit)_
 
 A typical install of GitLab will be on GNU/Linux. It uses Nginx or Apache as a web front end to proxypass the Unicorn web server. By default, communication between Unicorn and the front end is via a Unix domain socket but forwarding requests via TCP is also supported. The web front end accesses `/home/git/gitlab/public` bypassing the Unicorn server to serve static pages, uploads (e.g. avatar images or attachments), and precompiled assets. GitLab serves web pages and a [GitLab API](https://gitlab.com/gitlab-org/gitlab-ce/tree/master/doc/api) using the Unicorn web server. It uses Sidekiq as a job queue which, in turn, uses redis as a non-persistent database backend for job information, meta data, and incoming jobs.