Crack the System Design Interview - Puncsky CS Notebook

Crack the System Design Interview - Puncsky CS Notebook

1.3 Step 3. Discuss individual components and how they interact in detail

When we truly understand a system, we should be able to identify what each component is and explain how they interact with one another. Take these components in the above diagram and specify each one by one. This could lead to more general discussions, such as the three common topics in Section 2, and to more specific domains, like how to design the photo storage data layout…

1.3.1 Load Balancer

Generally speaking, load balancers fall into three categories:

• DNS Round Robin (rarely used): clients get a randomly-ordered list of IP addresses.
  • pros: easy to implement and free
  • cons: hard to control and not responsive, since DNS cache needs time to expire
• L3/L4 Load Balancer: traffic is routed by IP address and port. L3 is network layer (IP). L4 is session layer (TCP).
  • pros: better granularity, simple, responsive
• L7 Load Balancer: traffic is routed by what is inside the HTTP protocol. L7 is application layer (HTTP).

It is good enough to talk in this level of detail on this topic, but in case the interviewer wants more, we can suggest exact algorithms like round robin, weighted round robin, least loaded, least loaded with slow start, utilization limit, latency, cascade, etc.

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