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54. Circuit Breaker Pattern

Mini-Project: Circuit Breaker for Agent Tool Calls

A circuit breaker wrapper around agent tool calls that transitions between Closed, Open, and Half-Open states to prevent cascading failures when external services become unavailable.

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Description

Prevents cascading failures when an external service (API, database, LLM provider) becomes unavailable or degraded. Without a circuit breaker, an agent will keep retrying failed calls, wasting resources and potentially causing system-wide failures.

The circuit breaker monitors failure rates for external calls. It has three states: Closed (normal operation), Open (all calls fail fast without trying), and Half-Open (allows a test request to check if the service recovered). After a threshold of failures, the circuit "opens" and all subsequent calls return a fallback response immediately.

Architecture Diagram

stateDiagram-v2
    [*] --> Closed
    Closed --> Open: Failure threshold exceeded
    Open --> HalfOpen: Timeout expires
    HalfOpen --> Closed: Test request succeeds
    HalfOpen --> Open: Test request fails