express-service-readiness-middleware

express-service-readiness-middleware

This module provides express middleware for determining whether routes are exposed based on service critical dependency health.

When critical dependencies are not ready a 502 status code will be returned for non whitelisted routes.

Routes will still be exposed if non-critical dependencies are not ready!

Specific routes can also be whitelisted to be exposed if critical dependencies are not yet ready.

Installation

With npm

$ npm install express-service-readiness-middleware --save

Example usage

const {
  checkDependenciesHealth,
  createReadinessMiddleware,
  setLogger
} = require('express-service-readiness-middleware')

// if s logger is not set no informational logging will occur.  Logging can be set using the 'setLogger' function.  The object must have a 'log' function.
setLogger(console)

// create dependencies
const dependencies = [
  {
    name: 'dependency-one',
    data: {
      connectionString: 'protocol:://{user}:{password}/test'
    },
    critical: true,
    isReady: () => Promise.resolve(true),
    isHealthy: () => Promise.resolve(true) // optional, isReady is used if not defined
  }
]

// register the middleware, ideally you would do this before all other middlware
const config = { whitelistedPaths: [ '/liveness' ]}
app.use(createReadinessMiddleware(dependencies, config))

// check dependency health
const health = await checkDependenciesHealth(dependencies)

console.log(JSON.stringify(health, null, 2))
/*
^^ would output:
{
  "name": "dependency-one",
  "critical": true,
  "data":  {
    "connectionString": "protocol:://{user}:{password}/test",
  },
  "healthy": true
}
*/

API

createReadinessMiddleware

const readinessMiddleware = createReadinessMiddleware(dependencies, config)

dependencies

Array of dependency objects. A dependency has the following properties:

• name: (string) The name of the dependency
• data: (object) Informational data about the dependency
• critical: (boolean) Indicates whether the dependency is critical
• isReady: (Promise) Indicates whether the dependency is ready
• isHealthy: (Promise) Indicates whether the dependency is healthy
• retryIntervalInMilliseconds: (number) Interval in milliseconds in which to check if the dependency is ready

config (optional)

• retryIntervalInMilliseconds: (default: 2000) Interval in milliseconds in which to check if a dependency is ready.
• maximumWaitTimeForServiceReadinessInMilliseconds: (default: 30000) Maximum time in milliseconds to wait for all dependencies to be ready.
• whitelistedPaths: (default: []) Paths to still route traffic to even if dependencies are not yet ready.

checkDependenciesHealth

You may want to periodically check or expose an endpoint to check whether dependencies are healthy.

The checkDependenciesHealth will check all dependencies health and return a result. isHealthy will be used if defined on a dependency otherwise it will fallback to isReady.

const health = await checkDependenciesHealth(dependencies)

License

(MIT)

Copyright (c) 2023 Lee Crowe

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.