patterns

Circuit breaker resilience pattern with closed, open, and half-open states for protecting services from cascading failures with automatic recovery testing.

Full FlowZap Code

Client { # Client Application
n1: circle label:"Start"
n2: rectangle label:"Initiate service call"
n3: rectangle label:"Receive response"
n4: rectangle label:"Process fallback response"
n5: circle label:"End"
n1.handle(right) -> n2.handle(left)
n2.handle(bottom) -> CircuitBreaker.n6.handle(top) [label="Request"]
n3.handle(right) -> n5.handle(left)
n4.handle(right) -> n5.handle(left)
}
CircuitBreaker { # Circuit Breaker
n6: diamond label:"Circuit state?"
n7: rectangle label:"Allow request through"
n8: rectangle label:"Return cached fallback"
n9: rectangle label:"Increment failure count"
n10: diamond label:"Failure threshold reached?"
n11: rectangle label:"Open circuit"
n12: rectangle label:"Reset failure count"
n13: rectangle label:"Start half-open timer"
n6.handle(right) -> n7.handle(left) [label="Closed"]
n6.handle(bottom) -> n8.handle(top) [label="Open"]
n6.handle(left) -> n7.handle(top) [label="Half-Open"]
n7.handle(bottom) -> ExternalService.n14.handle(top) [label="Forward"]
n8.handle(top) -> Client.n4.handle(bottom) [label="Fallback"]
n9.handle(right) -> n10.handle(left)
n10.handle(right) -> n11.handle(left) [label="Yes"]
n10.handle(bottom) -> n12.handle(top) [label="No"]
n11.handle(right) -> n13.handle(left)
n12.handle(top) -> Client.n3.handle(bottom) [label="Success"]
n13.handle(top) -> Client.n4.handle(bottom) [label="Tripped"]
}
ExternalService { # External Service
n14: rectangle label:"Process request"
n15: diamond label:"Request successful?"
n16: rectangle label:"Return success response"
n17: rectangle label:"Return error response"
n14.handle(right) -> n15.handle(left)
n15.handle(right) -> n16.handle(left) [label="Yes"]
n15.handle(bottom) -> n17.handle(top) [label="No"]
n16.handle(top) -> CircuitBreaker.n12.handle(bottom) [label="OK"]
n17.handle(top) -> CircuitBreaker.n9.handle(bottom) [label="Error"]
}

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