README

Opossum Circuit Breaker Adapter ·

Circuit breaker adapter with Opossum.

Installation

Make sure we have the core module @Drizzle-Http/core installed.

npm i @drizzle-http/core
npm i @drizzle-http/opossum-circuit-breaker

Usage

Usage typically looks like the example below:

import { CircuitBreakerCallAdapterFactory } from "@drizzle-http/opossum-circuit-breaker";
import { DrizzleBuilder } from "@drizzle-http/core";
import { UndiciCallFactory } from "@drizzle-http/undici";
import { CircuitBreaker } from "@drizzle-http/opossum-circuit-breaker";
import { Fallback } from "@drizzle-http/opossum-circuit-breaker";
import { GET } from "@drizzle-http/core";

class CustomerApi {
  @GET('/customers')
  @CircuitBreaker({ /* Opossum CircuitBreaker.Options */ })
  @Fallback('customersAlt')
  customers(): Promise<Customer[]> { }
}

class CustomerApiFallbacks {
  customersAlt(id: string, error: Error): Promise<Customer> {
    // Fallback implementation
  }
}

const factory = new CircuitBreakerCallAdapterFactory({ options: { /* global options */ }, fallbacks: new CustomerApiFallbacks() })
const api = DrizzleBuilder
  .newBuilder()
  .baseUrl(/* base url */)
  .callFactory(new UndiciCallFactory())
  .addCallAdapterFactories(factory)
  .build()
  .create(CustomerApi)

Features

All functionalities from Opossum are available.
Some features and extensions:

Fallback

Fallback methods follow Opossum specification, same argument list and an error argument at the end.
There are 3 ways to specify a fallback for a circuit breaker:

Specify a fallback class in CircuitBreakerCallAdapterFactory constructor. If a method name matches the one specified in the API class, it will be used as a fallback automatically.
Apply the decorator @Fallback() and:
- If @Fallback() decorator argument is a string, it will try to find the method on the fallback class specified in the CircuitBreakerCallAdapterFactory constructor.
- If @Fallback decorator receives a function, this function will be the fallback.

Make sure the fallback methods have right signature: same argument list + error at the end and same return type.

Registry

All circuit breakers associated with a CircuitBreakerCallAdapterFactory are stored in a registry instance. CircuitBreakerCallAdapterFactory accepts a parameter registry. You can pass a custom Registry implementation.

The circuit breaker instance is only stored in the registry after the first execution. If you want to change the circuit breaker behaviour, prefer to use a LifeCycleListener implementation.

Usage no npm install needed!