What is a Circuit Breaker?

Circuit Breaker is a design pattern used to increase the resilience of distributed systems. It prevents continuous attempts to access a non-functioning service, helping to avoid cascading failures and excessive load.

Working principle:

• When a certain number of errors is exceeded, the Circuit Breaker "opens" and blocks further calls to the problematic service.
• After some time, it attempts to "close" the circuit and check if the service has recovered.
• If the service responds successfully, the Circuit Breaker returns to its normal state.

In Node.js, this is often implemented using libraries such as opossum.

Example of usage with the opossum library:

const CircuitBreaker = require('opossum');

function asyncServiceCall() {
  return new Promise((resolve, reject) => {
    // emulate call to an external service
    if (Math.random() > 0.7) resolve('Success');
    else reject('Failure');
  });
}

const breaker = new CircuitBreaker(asyncServiceCall, {
  timeout: 3000, // response timeout
  errorThresholdPercentage: 50, // error threshold for triggering
  resetTimeout: 5000 // time before attempting to recover
});

breaker.fire()
  .then(console.log)
  .catch(console.error);