What is the link between a fuse, Netflix and the Cloud ?

What is a Fuse ?

Protects appliances and wiring by monitoring failures

• Breaks the circuit when current flow is too high

• Needs manual re-set to close the circuit back

What is the Circuit Breaker pattern ?

Protects applications from catastrophic cascade by monitoring for failures

• Trips the circuit when failures reach a certain threshold

• Implements an automated re wiring process using threshold and half open state

Electric circuit breaker

• Switch oven on
• Power overhead
• Max current limit reached
• Fuse breaks - no more current flowing
• You (pissed) go and change the fuse , or press the CB
• The circuit is closed
• Time to heat up that pizza, at last !

Software circuit breaker

• Web app making a request
• Response latency
• Max failures / timespan reached
• CB opens - no more request sent
• Time to try again - CB is half open
• Transient fault on the remote is resolved
• Request succeeds - CB is Closed

What is Netflix Hystrix ?

Latency and fault tolerance library

Stop cascading failures

Fallbacks and graceful degradation

Fail fast and rapid recovery

=> A real life implementation of the Circuit Breaker Pattern