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    @fastify/circuit-breaker
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    3.0.0 • Public • Published

    @fastify/circuit-breaker

    CI NPM version js-standard-style

    A low overhead circuit breaker for your routes.

    Install

    npm i @fastify/circuit-breaker
    

    Usage

    Register the plugin and, if needed, pass it custom options.
    This plugin will add an onSend hook and expose a circuitBreaker utility.
    Call fastify.circuitBreaker() when declaring the preHandler option of a route, in this way you will put that very specific route under the circuit breaking check.

    const fastify = require('fastify')()
    
    fastify.register(require('@fastify/circuit-breaker'))
    
    fastify.register(function (instance, opts, next) {
      instance.route({
        method: 'GET',
        url: '/',
        schema: {
          querystring: {
            error: { type: 'boolean' },
            delay: { type: 'number' }
          }
        },
        preHandler: instance.circuitBreaker(),
        handler: function (req, reply) {
          setTimeout(() => {
            reply.send(
              req.query.error ? new Error('kaboom') : { hello: 'world' }
            )
          }, req.query.delay || 0)
        }
      })
      next()
    })
    
    fastify.listen(3000, err => {
      if (err) throw err
      console.log('Server listening at http://localhost:3000')
    })

    Options

    You can pass the following options during the plugin registration, in this way the values will be used in all routes.

    fastify.register(require('@fastify/circuit-breaker'), {
      threshold: 3, // default 5
      timeout: 5000, // default 10000
      resetTimeout: 5000, // default 10000
      onCircuitOpen: async (req, reply) => {
        reply.statusCode = 500
        throw new Error('a custom error')
      },
      onTimeout: async (req, reply) => {
        reply.statusCode = 504
        return 'timed out'
      }
    })
    • threshold: is the maximum number of failures accepted before opening the circuit.
    • timeout: is the maximum number of milliseconds you can wait before return a TimeoutError.
    • resetTimeout: number of milliseconds before the circuit will move from open to half-open
    • onCircuitOpen: async function that gets called when the circuit is open due to errors. It can modify the reply and return a string | Buffer | Stream payload. If an Error is thrown it will be routed to your error handler.
    • onTimeout: async function that gets called when the circuit is open due to timeouts. It can modify the reply and return a string | Buffer | Stream | Error payload. If an Error is thrown it will be routed to your error handler.

    Otherwise, you can customize every single route by passing the same options to the circuitBreaker utility:

    fastify.circuitBreaker({
      threshold: 3, // default 5
      timeout: 5000, // default 10000
      resetTimeout: 5000 // default 10000
    })

    If you pass the options directly to the utility, it will take precedence over the global configuration.

    Customize error messages

    If needed you can change the default error message for the circuit open error and the timeout error:

    fastify.register(require('@fastify/circuit-breaker'), {
      timeoutErrorMessage: 'Ronf...', // default 'Timeout'
      circuitOpenErrorMessage: 'Oh gosh!' // default 'Circuit open'
    })

    Caveats

    Since it is not possible to apply the classic timeout feature of the pattern, in this case the timeout will measure the time that the route takes to execute and once the route has finished if the time taken is higher than the timeout it will return an error, even if the route has produced a successful response.

    If you need a classic circuit breaker to wrap around an API call consider using easy-breaker.

    Acknowledgements

    Image curtesy of Martin Fowler.

    License

    MIT

    Copyright © 2018 Tomas Della Vedova

    Install

    npm i @fastify/circuit-breaker

    DownloadsWeekly Downloads

    198

    Version

    3.0.0

    License

    MIT

    Unpacked Size

    31.2 kB

    Total Files

    12

    Last publish

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