System Design Template

system-design-template.md

(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
            a) DNS
            b) CDN [Push vs Pull]
            c) Load Balancers [Active-Passive, Active-Active, Layer 4, Layer 7]
            d) Reverse Proxy
            e) Application layer scaling [Microservices, Service Discovery]
            f) 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
            g) 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
            h) Asynchronism
                    > Message queues
                    > Task queues
                    > Back pressure
            i) Communication
                    > TCP
                    > UDP
                    > REST
                    > RPC

(6) JUSTIFY [5 min]

(1) Throughput of each layer
(2) Latency caused between each layer
(3) Overall latency justification