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High-Level Design (HLD) Interview Guide: What to Cover

High-level design, often called HLD, is about the big picture: which components make up a system, how they talk to each other, and how the system scales and stays reliable. It is the main part of most system design interviews.

What interviewers look for

They want a clear architecture that meets the stated requirements, sensible choices, and the ability to explain trade-offs. Clarity beats cleverness.

Building blocks to know

Be able to explain what each of these does and when to use it: load balancers, application servers, relational and non-relational databases, caches, message queues, object storage, content delivery networks, and API gateways.

Also know the basics of replication, partitioning (sharding), indexing, and the trade-off between consistency and availability.

How to present your design

Start with requirements and rough scale, then draw the components and the data flow for the main use cases. Describe the data model and the key APIs. Then discuss bottlenecks and failure cases.

Common mistakes

Jumping to technology names before understanding the requirements, adding components with no reason, and ignoring failure handling are the most common problems. Justify each component by the problem it solves.

Where it fits

HLD is the architecture level. Class and object details belong to low-level design, which has its own guide. Practice both, since many interview loops include each.

Frequently asked questions

What is the difference between HLD and LLD?

HLD covers the overall architecture and components. LLD covers the internal design of a component, such as classes, interfaces and methods.

Which technologies should I name?

Name ones you understand, and explain why. Concepts matter more than brand names.

Put this into practice.

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