30-second elevator pitch: "Real-time updates require efficient push channels. I choose based on latency needs: polling for 2-5 second updates, long polling or SSE for near real-time, WebSockets when I need bidirectional low latency. The second hop is Pub/Sub or consistent hashing to fan out updates from the source to servers."

The Problem

Consider a colla…

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30-second elevator pitch: "Multi-step processes fail halfway - payment charged but inventory not reserved. I use workflow engines like Temporal or AWS Step Functions so each step is durable, failures trigger retries or compensation, and the system picks up exactly where it left off after a crash."

What You Will Learn

Approaches

- Single-server orchestratio…

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30-second elevator pitch: "Contention happens when two users act on the same data at once, like two people buying the last concert ticket. I fix it by making operations atomic, using locks when conflicts are common, or optimistic concurrency when they are rare. For distributed systems, I use sagas or two-phase commit. I always exhaust single-database so…

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30-second elevator pitch: "Caching stores frequently accessed data in memory so reads skip the database. I start with cache-aside using Redis as the default, add CDN for global static assets, and choose invalidation strategy based on freshness requirements. Cache-aside handles most scenarios, and I layer additional strategies only when the problem deman…

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30-second elevator pitch: "For any operation that takes more than a few seconds, I return a job ID immediately and process asynchronously. A message queue decouples submission from processing. Workers pull jobs, execute them, and update status. The client polls for completion or gets a webhook callback. I add exponential backoff for retries and a dead l…

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30-second elevator pitch: "Large files bypass my application server entirely. Clients get a presigned URL and upload directly to S3 in chunks. An S3 event triggers async processing like thumbnails or transcoding. Downloads go through a CDN. My server only handles metadata and authorization."

What You Will Learn

Upload Patterns

- Presigned URL upload (bypas…

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30-second elevator pitch: "Write scaling is harder than read scaling because every write must persist to disk. I exhaust vertical scaling and database tuning first. Then I shard by partition key to spread load linearly. For bursty traffic I add queues and load shedding. For extreme volume I batch writes and use hierarchical aggregation. Each tier builds…

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30-second elevator pitch: "Read traffic grows exponentially faster than writes. I handle this in three tiers: first optimize the existing database with indexes and denormalization, then scale horizontally with read replicas, and finally add caching layers. Each tier builds on the previous one, and I always start with the simplest solution."

The Problem

Co…

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