Moving billions of messages from MongoDB to Cassandra
How Discord escaped MongoDB tail-latency degradation by rethinking their message data model around Cassandra partition semantics.
Deadline driven preparation
Core Concepts
01Request and Response02DNS and CDN03Load Balancers and API Gateways04Parallelism and Concurrency05Storage06Numbers to Know07Back-of-the-Envelope Calculations08Indexes and MVCC09Caching10Queues and Retries11Distributed Systems and CAP12Replication13Sharding14Errors, Logs and Telemetry15Tokens, Embeddings and RAG
Low-Level Design
High-Level Design
GitTrack an AI wrapper from local setup through pull requests, recovery, and releases.
DockerShip a festival's video service with its dependencies, persistent media, and a repeatable deployment.
PostgresChoose a relational model for workshop bookings, then handle concurrent reservations and growing queries.
MongoDBModel an irregular equipment catalog with documents, validation, useful indexes, and safe updates.
RedisKeep a live quiz leaderboard, shared sessions, and bounded caches responsive across API instances.
KafkaLet parcel scans feed tracking, notifications, and analytics independently, with replay and retry handling.
CassandraDistribute a fleet’s temperature history around bounded partitions, predictable reads, and retention.
ElasticsearchFind the right runbook through imperfect queries, then evolve and rebuild its search index.
SnowflakeReconcile business reports across source systems without borrowing checkout’s compute.
KubernetesKeep a lunch-delivery API running through a rush, a failed node, and an application rollout.
HelmMaintain one webhook-relay chart for customer installations, with reviewed values and release history.
TerraformRecreate a signing service’s infrastructure through reviewed plans, shared state, and deliberate imports.
aws cliGrow a receipt-processing app through EC2, S3, SQS, RDS, ECR, EKS, and DynamoDB as each becomes useful.
BookShelf
Frontend Engineering
Build accessible interfaces that stay fast as applications grow.
Backend Engineering
Design reliable services that handle data and requests at scale.
DevOps
Package, deploy, and operate software with reliable releases.
High-Level Design (HLD)
Design distributed systems and reason through their tradeoffs.
Low-Level Design (LLD)
Model software with clear objects, interfaces, and responsibilities.
Language Fundamentals
Learn how five languages handle data, execution, and memory.
From fanout-on-write to hybrid delivery
How Twitter's news feed moved away from pre-computing timelines for all followers as accounts reached millions of followers.
The BGP leak that took down Cloudflare
How a single misconfigured route advertisement propagated globally and what Cloudflare changed about their route filtering and BGP safety nets.
The Slack message storm incident
How a feedback loop between presence updates and reconnecting clients took down Slack and what changes in their notification and connection handling prevented recurrence.