System design interview template

src: https://leetcode.com/discuss/career/229177/My-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
        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

(7) Key metrics to measure

For example, in the case of designing a search system, we will be interested to see how many keywords are resulting in blank search results. Here the ratio of search hits is important so we also need to know the number of search queries we are receiving per minute. We can use tools like Graphana with Prometheus, AppDynamics, etc.

(8) System health monitoring

Measuring app index, the latency of microservices We can use Newrelic, AppDynamics

(9) Log systems

We can use ELK(Elastic, Logstash, Kibana) or Logtail, etc.