Add system design template link

SystemDesignTemplate.md

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+# System Design Template
+
+### (1) FEATURE EXPECTATIONS [5 min]
+
+```
+1. Use cases
+2. Scenarios that will not be covered
+3. Who will use
+4. How many will use
+5. Usage patterns
+```
+
+### (2) ESTIMATIONS [5 min]
+
+```
+1. Throughput (QPS for read and write queries)
+2. Latency expected from the system (for read and write queries)
+3. Read/Write ratio
+4. Traffic estimates
+	- Write (QPS, Volume of data)
+	- Read  (QPS, Volume of data)
+5. Storage estimates
+6. Memory estimates
+	- If we are using a cache, what is the kind of data we want to store in cache
+	- How much RAM and how many machines do we need for us to achieve this ?
+	- Amount of data you want to store in disk/ssd
+```
+### (3) DESIGN GOALS [5 min]
+
+```
+1. Latency and Throughput requirements
+2. Consistency vs Availability  [Weak/strong/eventual => consistency | Failover/replication => availability]
+```
+
+### (4) HIGH LEVEL DESIGN [5-10 min]
+
+```
+1. APIs for Read/Write scenarios for crucial components
+2. Database schema
+3. Basic algorithm
+4. High level design for Read/Write scenario
+```
+
+### (5) DEEP DIVE [15-20 min]
+
+```
+1. Scaling the algorithm
+2. Scaling individual components: 
+	- Availability, Consistency and Scale story for each component
+	- Consistency and availability patterns
+3. Think about the following components, how they would fit in and how it would help
+	- DNS
+ 	- CDN [Push vs Pull]
+ 	- Load Balancers [Active-Passive, Active-Active, Layer 4, Layer 7]
+ 	- Reverse Proxy
+ 	- Application layer scaling [Microservices, Service Discovery]
+ 	- DB [RDBMS, NoSQL]
+		- RDBMS 
+			- Master-slave, Master-master, Federation, Sharding, Denormalization, SQL Tuning
+		- NoSQL
+			- Key-Value, Wide-Column, Graph, Document
+			- Fast-lookups:        
+ 				- RAM  [Bounded size] => Redis, Memcached
+ 				- AP [Unbounded size] => Cassandra, RIAK,Voldemort
+ 				- CP [Unbounded size] => HBase, MongoDB,Couchbase, DynamoDB
+	- Caches
+		- Client caching, CDN caching, Webserver caching, Database caching, Application caching, Cache @Query level, Cache @Object level
+		- Eviction policies:
+			- Cache aside
+			- Write through
+			- Write behind
+			- Refresh ahead
+			- Asynchronism
+			- Message queues
+			- Task queues
+			- Back pressure
+			- Communication
+			- TCP
+			- UDP
+			- REST
+			- RPC
+```
+
+### (6) JUSTIFY [5 min]
+
+```
+1. Throughput of each layer
+2. Latency caused between each layer
+3. Overall latency justification
+```
+
+References:
+
+1. https://leetcode.com/discuss/career/229177/My-System-Design-Template