Tag: circuit breaker pattern

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I’m an experienced mountain climber (I know, I’m pretty cool), standing at the base of a challenging peak. Each time I face this mountain, I must assess the weather conditions before making my ascent. In this scenario, the mountain represents an external service my Node.js application depends on, and the weather conditions symbolize the service’s current availability and reliability.

Before I start climbing, I have my trusty circuit breaker, akin to a seasoned expedition guide. This guide helps me decide whether it’s safe to proceed or if I should hold off until conditions improve. As I begin my journey, the guide keeps a close eye on the weather, just as a circuit breaker monitors the success or failure of requests to the external service.

If the weather starts to turn sour and becomes dangerous, my guide advises me to stop and wait. Similarly, if the circuit breaker detects a series of failures in the external service, it trips and halts further requests. This prevents my application from wasting resources on a service that is currently down, much like how I avoid risking my life in hazardous conditions.

While we wait, my guide allows me to try a different path occasionally to check if the weather has improved. This mirrors the circuit breaker’s “half-open” state, where it permits a limited number of requests to see if the service has recovered. If the weather clears up and conditions are favorable again, my guide gives me the green light to proceed with my climb. Likewise, if the external service starts responding successfully, the circuit breaker closes, and my application resumes normal operations.

In this way, the circuit breaker pattern in my Node.js application acts as a wise guide, ensuring that I only make the climb when it’s safe, preserving my energy and resources. By implementing this pattern, I can maintain the stability and resilience of my application in the face of potential service disruptions.

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Here’s a basic example of how I might set up a circuit breaker using opossum:

const CircuitBreaker = require('opossum');

function climbMountain() {
  // Simulating a request to an external service
  return new Promise((resolve, reject) => {
    //  this is where we check the weather or service availability
    const serviceIsAvailable = Math.random() > 0.5;
    if (serviceIsAvailable) {
      resolve('Climb successful!');
    } else {
      reject('Weather conditions are bad, climb aborted.');
    }
  });
}

// Create a circuit breaker for the climbMountain function
const breaker = new CircuitBreaker(climbMountain, {
  timeout: 3000, // 3 seconds timeout for the request
  errorThresholdPercentage: 50, // Open the circuit if 50% of requests fail
  resetTimeout: 10000 // After 10 seconds, try again
});

breaker.fallback(() => 'Fallback: Staying at base camp, waiting for better conditions.');

breaker.on('open', () => console.log('Circuit is open. Halting further climbs.'));
breaker.on('halfOpen', () => console.log('Circuit is half-open. Testing the conditions.'));
breaker.on('close', () => console.log('Circuit is closed. Resuming climbs.'));

async function attemptClimb() {
  try {
    const result = await breaker.fire();
    console.log(result);
  } catch (error) {
    console.log(`Error: ${error}`);
  }
}

// Attempt multiple climbs to see the circuit breaker in action
setInterval(attemptClimb, 2000);

In this example, the climbMountain function represents a potentially unreliable operation, such as calling an external API. The CircuitBreaker is configured with rules similar to our guide’s assessment of weather conditions: it times out requests after 3 seconds, opens the circuit if more than 50% of requests fail, and waits 10 seconds before attempting to close the circuit again.

Key Takeaways:

1. Resource Management: A circuit breaker helps manage resources by preventing wasted requests to unreliable services, similar to avoiding dangerous climbs in bad weather.
2. Resilience: By implementing a circuit breaker, applications can become more resilient, maintaining stability even when dependent services fail temporarily.
3. Monitoring and Feedback: Just as a guide monitors conditions, a circuit breaker provides feedback through events like ‘open’, ‘halfOpen’, and ‘close’, helping developers understand service reliability and application behavior.