Add index section

README.md

@@ -78,3 +78,93 @@ Feel free to submit pull requests to help:
 Content that needs some polishing is placed [under development](#under-development).
 
 Review the [Contributing Guidelines](https://github.com/donnemartin/awesome-aws/blob/master/CONTRIBUTING.md).
+
+## Index of system design topics
+
+> Summaries of various system design topics, including pros and cons.  **Everything is a trade-off**.
+>
+> Each section contains links to more in-depth resources.
+
+![Imgur](http://i.imgur.com/jj3A5N8.png)
+
+* [System design topics: start here](#system-design-topics-start-here)
+    * [Step 1: Review the scalability video lecture](#step-1-review-the-scalability-video-lecture)
+    * [Step 2: Review the scalability article](#step-2-review-the-scalability-article)
+    * [Next steps](#next-steps)
+* [Performance vs scalability](#performance-vs-scalability)
+* [Latency vs throughput](#latency-vs-throughput)
+* [Availability vs consistency](#availability-vs-consistency)
+    * [CAP theorem](#cap-theorem)
+        * [CP - consistency and partition tolerance](#cp-consistency-and-partition-tolerance)
+        * [AP - availability and partition tolerance](#ap-availability-and-partition-tolerance)
+* [Consistency patterns](#consistency-patterns)
+    * [Weak consistency](#weak-consistency)
+    * [Eventual consistency](#eventual-consistency)
+    * [Strong consistency](#strong-consistency)
+* [Availability patterns](#availability-patterns)
+    * [Fail-over](#fail-over)
+    * [Replication](#replication)
+* [Domain name system](#domain-name-system)
+* [Content delivery network](#content-delivery-network)
+    * [Push CDNs](#push-cdns)
+    * [Pull CDNs](#pull-cdns)
+* [Load balancer](#load-balancer)
+    * [Active-passive](#active-passive)
+    * [Active-active](#active-active)
+    * [Layer 4 load balancing](#layer-4-load-balancing)
+    * [Layer 7 load balancing](#layer-7-load-balancing)
+    * [Horizontal scaling](#horizontal-scaling)
+* [Reverse proxy (web server)](#reverse-proxy-web-server)
+    * [Load balancer vs reverse proxy](#load-balancer-vs-reverse-proxy)
+* [Application layer](#application-layer)
+    * [Microservices](#microservices)
+    * [Service discovery](#service-discovery)
+* [Database](#database)
+    * [SQL](#sql)
+        * [Relational database management system (RDBMS)](relational-database-management-system-rdbms)
+        * [Scaling SQL](#scaling-sql)
+            * [Master-slave replication](#master-slave-replication)
+            * [Federation](#federation)
+            * [Sharding](#sharding)
+            * [Denormalization](#denormalization)
+            * [SQL tuning](#sql-tuning)
+    * [NoSQL](#nosql)
+        * [Key-value store](#key-value-store)
+        * [Document store](#document-store)
+        * [Wide column store](#wide-column-store)
+        * [Graph Database](#graph-database)
+    * [SQL or NoSQL](#sql-or-nosql)
+* [Cache](#cache)
+    * [Client caching](#client-caching)
+    * [CDN caching](#cdn-caching)
+    * [Web server caching](#web-server-caching)
+    * [Database caching](#database-caching)
+    * [Application caching](#application-caching)
+    * [Caching at the database query level](#caching-at-the-database-query-level)
+    * [Caching at the object level](#caching-at-the-object-level)
+    * [When to update the cache](#when-to-update-the-cache)
+        * [Cache-aside](#cache-aside)
+        * [Write-through](#write-through)
+        * [Write-behind (write-back)](#write-behind-write-back)
+        * [Refresh-ahead](#refresh-ahead)
+* [Asynchronism](#asynchronism)
+    * [Message queues](#message-queues)
+    * [Task queues](#task-queues)
+    * [Back pressure](#back-pressure)
+* [Communication](#communication)
+    * [Transmission control protocol (TCP)](#transmission-control-protocol-tcp)
+    * [User datagram protocol (UDP)](#user-datagram-protocol-udp)
+    * [Remote procedure call (RPC)](#remote-procedure-call-rpc)
+    * [Representational state transfer (REST)](#representational-state-transfer-rest)
+* [Security](#security)
+* [Appendix](#appendix)
+    * [Powers of two table](#powers-of-two-table)
+    * [Latency numbers every programmer should know](#latency-numbers-every-programmer-should-know)
+* [Under development](#under-development)
+    * [Distributed computing](#distributed-computing)
+    * [Consistent hashing](#consistent-hashing)
+    * [Scatter gather](#scatter-gather)
+    * [Contribute](#contributing)
+* [Credits](#credits)
+* [Contact info](#contact-info)
+* [License](#license)