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

Updated the docs with some recent information

Closes #787

See merge request !9

README.md

@@ -2,7 +2,9 @@
 [These are not the runbooks you are looking for](https://gitlab.com/gitlab-com/runbooks)
-[Infrastructure Overview](overview.md)
+## I'm here to see how the GitLab.com infrastructure is made
+
+You should read the [production architecture](production_architecture.md) then.
 ## Where and how to look for data
@@ -31,9 +33,3 @@ There are some metrics that are not visible in this public site because we do no
 * [Host Stats](http://performance.gitlab.net/dashboard/db/host-stats): useful to dive deep into a specific host to understand what is going on with it. Select a host from the dropdown on the top.
 * [Business Stats](http://performance.gitlab.net/dashboard/db/business-stats): shows many pushes, new repos and CI builds.
 * [Daily overview](http://performance.gitlab.net/dashboard/db/daily-overview): shows endpoints with amount of calls and performance metrics. Useful to understand what is slow generally.
-
-## Production Architecture
-
-![Architecture](img/GitLab Infrastructure Architecture.png)
-
-[Source](https://docs.google.com/drawings/d/1MqoemFRdoLm3_p5aKBhzblZM872F1R-tWdoOR5xMQpE/edit), GitLab internal use only

overview.md → production_architecture.md

-# Infrastructure Overview
+# Production Architecture
 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.
+This is what it looks like:
+
+![Architecture](img/GitLab Infrastructure Architecture.png)
+[Source](https://docs.google.com/drawings/d/1MqoemFRdoLm3_p5aKBhzblZM872F1R-tWdoOR5xMQpE/edit), GitLab internal use only
+
 ## Azure
 The main portion of GitLab.com is hosted on Microsoft Azure. We have
@@ -12,23 +17,38 @@ 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
+* 22 front-end nodes of which:
+  * 4 are Web nodes
+  * 8 are API nodes
+  * 10 are Git nodes
+* 10 Sidekiq nodes
+* 4 PostgreSQL servers
 * 5 Redis servers
-* 3 Prometheus monitoring servers
-* 11 NFS servers
+* 3 Prometheus servers
+* 5 NFS servers
+
+Note that these numbers can fluctuate to adapt to the platform needs.
 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.
+All our servers run the latest Ubuntu LTS unless there is a specific need to do otherwise. Every server is configured with a fully fledged set of firewall rules for increased security.
+### Load Balancers
+
+We utilize Azure load balancers in front of our HAProxy nodes. This allows us to leverage on the Azure infrastructure for HA as well as [taking advantage of the power of HAProxy](https://gitlab.com/gitlab-cookbooks/gitlab-haproxy).
+
+Additionally, we utilize an Azure load balancer to manage PostgreSQL failovers.
+
+* The GitLab.com load balancer pool serves git over ssh, git over https, http and https traffic.
+* The GitLab Pages load balancer serves http and https.
+* The AltSSH load balancer serves [git on port 443](https://about.gitlab.com/2016/02/18/gitlab-dot-com-now-supports-an-alternate-git-plus-ssh-port/) and translates it to port 22 on the back-end.
+
+### Service nodes
+Different services have different resource utilization patterns so we use a variety of instance types across our service nodes that are consistent for each group. We have recently isolated traffic by type on dedicated pools of nodes. We hope you noticed the performance improvement.
 ## Digital Ocean
@@ -59,7 +79,7 @@ We are currently investigating Google Cloud.
 # Technology at GitLab
-We use a lot of cool ([but boring](https://about.gitlab.com/handbook/#values)])
+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)
@@ -68,3 +88,5 @@ technologies here at GitLab. Below is a non-exhaustive list of tech we use here.
 * [PostgreSQL](https://www.postgresql.org/)
 * [Redis](https://redis.io/)
 * [ELK Stack](https://www.elastic.co/products)
+* [Terraform](https://www.terraform.io)
+* [Consul](https://www.consul.io)