In this post, we'll take a look at how to use circuit breakers to build more resilient backend systems. We'll first define what a circuit breaker is and how it works. We'll then see how to use a circuit breaker in a simple Node.js application.
A circuit breaker is a software design pattern that is used to increase the resilience of systems. It does this by providing a mechanism to detect when a system is unavailable or unresponsive, and by failing fast and gracefully when this is the case.
The idea behind circuit breakers is that they can prevent cascading failures. If one part of a system is unavailable, the circuit breaker can prevent other parts of the system from trying to access it, and thus prevent them from becoming unavailable as well.
A circuit breaker has three states: closed
, open
, and half-open
.
In the closed
state, the circuit breaker allows requests to pass through to the backend system. If the backend system is unavailable or unresponsive, the circuit breaker will transition to the open
state.
In the open
state, the circuit breaker will not allow any requests to pass through. This is to prevent the backend system from becoming overloaded. After a period of time, the circuit breaker will transition to the half-open
state.
In the half-open
state, the circuit breaker will allow a limited number of requests to pass through. This is to allow the backend system to recover. If the backend system is still unavailable or unresponsive, the circuit breaker will transition back to the open
state.
Let's see how to use a circuit breaker in a simple Node.js application. We'll use the opossum
library.
First, we need to install the opossum
library:
npm install opossum
Next, we need to require the library:
const opossum = require('opossum');
Now, we can create a circuit breaker:
const circuitBreaker = new opossum.CircuitBreaker(function () {
// This is the function that will be called when the circuit breaker is `closed`
// It should return a promise that resolves when the backend system is available
// and rejects when the backend system is unavailable
});
We can now use the circuitBreaker
object to make requests to the backend system:
circuitBreaker.fire()
.then(function (result) {
// The request was successful
})
.catch(function (err) {
// The request failed
});
If the backend system is unavailable or unresponsive, the fire
method will return a rejected promise, and the catch
handler will be executed.
In this post, we've seen how to use circuit breakers to build more resilient backend systems. We've seen how circuit breakers work, and how to use them in a simple Node.js application.