19-Usage-Billing-Engine

Appearance

14.17 Classic System Design Problems ​

1. Designing AWS CloudWatch Billing ​

  • Requirements: Ingest 100M telemetry metrics/sec; bill customers per metric alarm and metric stream.
  • Architecture: Ingestion fronted by AWS Kinesis; continuous aggregation in Apache Flink; hourly aggregates committed to DynamoDB; billing period reconciliation queries pre-aggregated rollups.

2. Designing a High-Throughput URL Shortener ​

  • Requirements: 10,000 writes/sec, 100,000 reads/sec.
  • Architecture: Base62 encoding on distributed 64-bit sequence counters; Redis cache with LRU eviction for top 20% hot URLs; Cassandra / PostgreSQL backing store.

3. 30-Second Interview Answer ​

"The building blocks of our billing engine—idempotent ingestion, sequence counter locking, and double-entry journals—apply directly to classic system design problems like AWS CloudWatch Billing or distributed rate limiters. In every case, the key is decoupling high-speed ingestion via streaming buffers from durable transactional storage."