What is a circuit breaker, and how does it prevent cascading failures? Mention bulkheads too.

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A circuit breaker protects against cascading failure. When a dependency is slow, every call ties up caller resources, threads and connections, waiting on doomed requests. If your timeout is 30 seconds and you have a pool of 200 threads, a dependency that stops responding drains that pool in seconds, and then the caller itself starts failing and the problem propagates upstream. One slow dependency takes down the whole chain. The breaker counts failures, and once they cross a threshold, say 50 percent of the last 20 calls, it opens, and subsequent calls fail fast in about a millisecond instead of hanging. After a cool off, typically around 30 seconds, it goes half open and lets a single trial request through. If that succeeds it closes and normal traffic resumes, if not it stays open. Two things make this powerful. Failing fast frees the caller resources so it stays healthy, and not hammering a struggling dependency gives it room to recover, which is what actually breaks the cascade. The complementary pattern is the bulkhead. I isolate resources per dependency, so each downstream gets its own thread or connection pool, maybe 20 threads each rather than one shared pool of 200. Then one slow dependency can only exhaust its own compartment. The name comes from ship compartments, a breach floods one compartment, not the whole hull. Together, breakers and bulkheads stop a single failing dependency from sinking the entire service.

Answer

What do the open, closed, and half-open states mean?

Closed = normal, calls pass; open = tripped, calls fail fast without hitting the dependency; half-open = a trial period letting one/few calls through to test recovery, closing if they succeed.

Answer

How does a bulkhead differ from a circuit breaker?

A breaker stops calling a failing dependency; a bulkhead isolates resources (separate pools per dependency) so one slow dependency cannot consume the resources others need. They complement each other.

What is a circuit breaker, and how does it prevent cascading failures? Mention bulkheads too.

What is a circuit breaker, and how does it prevent cascading failures? Mention bulkheads too.

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