Express Circuit Breaker

Provides error protection within an express route

• Express Circuit Breaker
  • Installation
  • Usage
    • API
      • opts.catchError(e)
      • opts.handleLater = false
      • opts.handleBlockedRequest(req, res)
    • Workflow
  • Example implementation

Installation

npm i express-circuit-breaker

var breaker = require('express-circuit-breaker')

Usage

express-circuit-breaker produces a middleware that will block requests if an error was thrown from a previous use.

API

For breaker(opts)

opts.catchError(e)

Called when a child node throws an error. Must return trip or reset.

• return 'trip': Trips the breaker and blocks future requests
• return 'reset': Resets the breaker to it's untripped state and allows future requests

opts.handleLater = false

Does not block request, instead allows request to be handled by next middleware. Breaker status is communicated in the req.breakerTripped. If true, breaker will not run handleBlockedRequest.

opts.handleBlockedRequest(req, res)

A middleware for handling incoming requests that were blocked by the breaker

Workflow

request(/protected) -> server -> breaker(open) -> endpoint

      |
      V

request(receives error 500) <- server <- breaker(tripped) <- endpoint(throws error)

Then later...

request(/protected) -> server <- breaker(tripped, sends back 500) -- endpoint(never touched)

Example implementation

var app = require('express')()
var breaker = require('express-circuit-breaker')

var CB = breaker({
  catchError: e => 'trip',
  handleBlockedRequest: (req, res) => res.sendStatus(500)
})

app.get('/unprotected', (req, res) => res.sendStatus(200))

app.get('/protected', CB, (req, res) => res.sendStatus(200))