Distributed Cache
Consistent hashing with virtual nodes, stampede prevention, slab allocation, hot keys that sharding cannot fix, and invalidation that is actually correct.
Rate Limiter
Token bucket vs sliding window, atomic Lua enforcement, cross-region drift, fail-open policy, and the hot tenant that melts one Redis shard.
Job Scheduler
Leader election with fencing tokens, hierarchical timing wheels, lease-based worker eviction, idempotent execution, and the thundering herd at every :00.
Notification System
Cross-channel deduplication, provider failover, quiet hours across time zones, priority lanes so OTPs never queue behind marketing, and 100M-user broadcasts.
Metrics Monitoring
High-cardinality time series, Gorilla compression, ingestion at 100M points/sec, rollups, alert evaluation at scale, and defending the TSDB from your own users.