- 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.
- AWS – SNS: Fan-out, Filtering and SQS Subscriptions
SNS pushes, SQS pulls, and the useful thing is putting them together: one topic, several queues, each consumer at its own pace. Topics and subscriptions, the confirmation handshake an HTTP endpoint has to complete, message filtering so a consumer is not woken for events it ignores, and the raw message delivery setting that stops your payload arriving wrapped in an envelope you did not ask for.
- MongoDB – $lookup, $unwind and $facet
Joining collections in an aggregation, flattening arrays, running several pipelines at once — and the strict type match that makes a join return nothing.