- Designing Amazon
An e-commerce system at the scale where every easy answer stops working. Catalog modelling for wildly different product types, search and faceting, the cart that must survive a logout, inventory reservation and oversell, the order state machine and why payment is a saga rather than a transaction, fulfilment across warehouses, and recommendations that are computed offline rather than at request time.
- AWS – Kinesis: Streams, Firehose and When to Use SQS Instead
Most teams reaching for Kinesis want SQS, so this starts with the table that tells them apart: replay, ordering, and many consumers reading the same records. Then shards and the partition key that decides your hot shard, the retention window, and Data Firehose for the case where you only wanted the data in S3. Note the names changed — Firehose and Managed Service for Apache Flink are not called Kinesis now.
- MongoDB – Replication and Sharding
Replica sets, the oplog, read preference and write concern — and an honest look at when sharding is the answer and when it is not.
- AWS – Elastic Beanstalk, and Whether to Use It in 2026
Beanstalk still works and still deploys a web app in one command, and it is still the fastest path from a zip file to a URL with a load balancer in front. What it actually creates on your behalf, `.ebextensions` and where the abstraction leaks, the deployment policies and which ones can serve two versions at once — and an honest comparison against ECS Fargate and App Runner before you commit.
- MongoDB – Atomicity and Transactions
Single-document atomicity covers more than you would think. What multi-document transactions cost, and when you genuinely need one.