Add Reverse proxy section

README.md

@@ -802,3 +802,46 @@ Load balancers can also help with horizontal scaling, improving performance and
 * [Layer 4 load balancing](https://www.nginx.com/resources/glossary/layer-4-load-balancing/)
 * [Layer 7 load balancing](https://www.nginx.com/resources/glossary/layer-7-load-balancing/)
 * [ELB listener config](http://docs.aws.amazon.com/elasticloadbalancing/latest/classic/elb-listener-config.html)
+
+## Reverse proxy (web server)
+
+<p align="center">
+  <img src="http://i.imgur.com/p7xHS4Z.png">
+  <br/>
+  <i><a href=https://commons.wikimedia.org/wiki/File:Proxy_concept_en.svg>Source: Wikipedia</a></i>
+  <br/>
+</p>
+
+A reverse proxy is a web server that centralizes internal services and provides unified interfaces to the public.  Requests from clients are forwarded to a server that can fulfill it before the reverse proxy returns the server's response to the client.
+
+Additional benefits include:
+
+* **Increased security** - Hide information about backend servers, blacklist IPs, limit number of connections per client
+* **Increased scalability and flexibility** - Clients only see the reverse proxy's IP, allowing you to scale servers or change their configuration
+* **SSL termination** - Decrypt incoming requests and encrypt server responses so backend servers do not have to perform these potentially expensive operations
+    * Removes the need to install [X.509 certificates](https://en.wikipedia.org/wiki/X.509) on each server
+* **Compression** - Compress server responses
+* **Caching** - Return the response for cached requests
+* **Static content** - Serve static content directly
+    * HTML/CSS/JS
+    * Photos
+    * Videos
+    * Etc
+
+### Load balancer vs reverse proxy
+
+* Deploying a load balancer is useful when you have multiple servers.  Often, load balancers  route traffic to a set of servers serving the same function.
+* Reverse proxies can be useful even with just one web server or application server, opening up the benefits described in the previous section.
+* Solutions such as NGINX and HAProxy can support both layer 7 reverse proxying and load balancing.
+
+### Disadvantage(s): reverse proxy
+
+* Introducing a reverse proxy results in increased complexity.
+* A single reverse proxy is a single point of failure, configuring multiple reverse proxies (ie a [failover](https://en.wikipedia.org/wiki/Failover)) further increases complexity.
+
+### Source(s) and further reading
+
+* [Reverse proxy vs load balancer](https://www.nginx.com/resources/glossary/reverse-proxy-vs-load-balancer/)
+* [NGINX architecture](https://www.nginx.com/blog/inside-nginx-how-we-designed-for-performance-scale/)
+* [HAProxy architecture guide](http://www.haproxy.org/download/1.2/doc/architecture.txt)
+* [Wikipedia](https://en.wikipedia.org/wiki/Reverse_proxy)