Distributed systems patterns every backend engineer should know

Building distributed systems is hard because the assumptions that work on a single machine break down at scale. Networks are unreliable, clocks are imprecise, and partial failures are the norm. Learning the core patterns helps you build systems that survive these realities.

The saga pattern manages distributed transactions across multiple services. Instead of a two-phase commit, a saga breaks the transaction into a series of local transactions with compensating actions for rollback. If step three fails, the saga executes the compensation for steps two and one. Sagas can be choreographed or orchestrated. Choreographed sagas are more decoupled but harder to reason about. Orchestrated sagas are easier to debug but create a central point of coordination.

The outbox pattern ensures reliable message publishing. When a service needs to publish an event as part of a database transaction, it writes the event to an outbox table in the same database transaction. A separate process reads the outbox and publishes the events. This guarantees that the event is published if and only if the transaction commits, eliminating the dual-write problem.

The circuit breaker pattern prevents cascading failures. When a downstream service starts failing, the circuit breaker trips and subsequent calls fail immediately without attempting the call. After a timeout, the circuit allows a few test requests to see if the service has recovered. This gives the failing service time to recover without being overwhelmed by retries.

The bulkhead pattern isolates failures by partitioning resources. Each service or component gets its own thread pool and connection pool. A failure in one partition cannot consume resources from another. This prevents a noisy neighbor from taking down the entire system.

Leader election picks one node to coordinate a group of replicas. Algorithms like Raft and Paxos ensure that at most one leader exists at any time. Leader election is essential for systems that need a single writer or coordinator.

The sidecar pattern deploys helper functionality alongside your main service in a separate container. Sidecars handle cross-cutting concerns like logging, monitoring, and service mesh traffic management without modifying the main application code.

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Rizwan Saleem | https://rizwansaleem.co