Merge branch 'infra-overview-doc' into 'master'

Add Overview Doc

See merge request !6

README.md

@@ -2,6 +2,8 @@
 [These are not the runbooks you are looking for](https://gitlab.com/gitlab-com/runbooks)
+[Infrastucture Overview](overview.md)
+
 ## Where and how to look for data
 ### General System Health

overview.md

+# Infrastructure Overview
+
+Our core infrastructure is currently hosted on several cloud providers,
+all with different functions. This document does not cover servers that
+are not integral to the public facing operations of GitLab.com. 
+
+## Azure
+
+The main portion of GitLab.com is hosted on Microsoft Azure. We have
+the following servers there.
+
+* 5 HAProxy load balancers for GitLab.com
+* 2 HAProxy load balancers for GitLab Pages
+* 2 HAProxy nodes for altssh.GitLab.com
+* 20 worker nodes (Nginx, Workhorse, Unicorn + Rails, Redis + Sidekiq)
+* 2 PostgreSQL servers
+* 5 Redis servers
+* 3 Prometheus monitoring servers
+* 11 NFS servers
+
+We also use availability sets to ensure that a minimum number of servers in each
+group are available at any given time. This ensures that Azure will not reboot
+all instances in the same availability set at the same time for anything that
+is planned.
+
+Additionally, we utilize an Azure load balancer to manage PostgreSQL failovers
+and to front-end the HA-Proxy servers with a single virtual IP address.
+
+![Architecture](img/GitLab Infrastructure Architecture.png)
+
+This constitutes our core infrastructure.
+
+## Digital Ocean
+
+Digital Ocean houses several servers that do not need to directly interact
+with our main infrastructure. There are many of these that do a variety of
+things, however not all will be listed here.
+
+The primary things on Digital Ocean at this time are: 
+
+* Chef Configuration Management Servers
+* Blackbox monitoring servers
+* Shared runner managers
+* Runner cache servers
+* ELK servers
+
+## AWS
+
+We host our DNS with route53 and we have several EC2 instances for various
+purposes. The servers you will interact with most are listed Below
+
+* Version
+* Mattermost
+* License
+
+## Google Cloud
+
+We are currently investigating Google Cloud.
+
+# Technology at GitLab
+
+We use a lot of cool ([but boring](https://about.gitlab.com/handbook/#values)])
+technologies here at GitLab. Below is a non-exhaustive list of tech we use here.
+
+* [Ruby](https://www.ruby-lang.org/) (probably goes without saying)
+* [Chef](https://www.chef.io/chef/)
+* [Prometheus](https://prometheus.io/)
+* [PostgreSQL](https://www.postgresql.org/)
+* [Redis](https://redis.io/)
+* [ELK Stack](https://www.elastic.co/products)