About Circuit Breaker Simulator

Simulate circuit breaker state transitions and failure recovery scenarios. Part of the DevTools Surf developer suite. Browse more tools in the Developer Utilities collection.

Use Cases

• Simulate a flapping downstream service to tune failure threshold parameters
• Demonstrate circuit breaker state transitions (closed, open, half-open) to team members
• Design retry budget policies for external API dependencies
• Plan resilience architecture for microservice dependency graphs

Tips

• Set the failure threshold percentage and minimum request count before the circuit opens — too sensitive and it trips on transient errors; too lenient and it fails to protect downstream services
• The half-open state timeout controls how quickly the circuit allows probe requests after tripping — tune this based on your dependency's typical recovery time
• Use the concurrent request slider to simulate traffic spikes and see how the circuit breaker limits cascading failure under load

Fun Facts

• The circuit breaker pattern in software was popularized by Michael Nygard in his book 'Release It!' (2007) — one of the first books to systematically describe resilience patterns for distributed systems. Netflix's Hystrix library (2011) made it mainstream.
• Netflix's Hystrix library, which popularized the circuit breaker pattern in microservices, was deprecated in 2018. It was succeeded by Resilience4j, which uses a functional (non-blocking) design compatible with reactive frameworks.
• Electrical circuit breakers were invented by Charles Grafton Page in 1836. The software pattern borrowed the name because it has the same function: automatically interrupting a fault before it causes damage to the broader system.

FAQ

What are the three circuit breaker states?

Closed (normal operation — requests pass through), Open (circuit tripped — requests fail fast without calling the dependency), Half-Open (test state — a single probe request is allowed to check if the dependency has recovered).

How is a circuit breaker different from a timeout?

A timeout waits for a slow response and eventually gives up. A circuit breaker monitors failure rates and proactively stops sending requests after a threshold is crossed — protecting the downstream service from additional load while it recovers.

Where should circuit breakers be placed in an architecture?

At every external dependency boundary: outbound HTTP calls, database queries, message queue consumers, and third-party API calls. Each should have independently configured thresholds based on that dependency's SLA.