express-service-readiness-middleware

express-service-readiness-middleware

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

When critical dependencies are not ready the middleware will intercept requests and a 502 status code will be returned for non whitelisted routes.

Once the service has been deemed ready it will be ready for its lifetime. So if a critical dependency goes down a 502 status code WILL NOT be returned for non whitelisted routes.

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

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

Installation

With npm

$ npm install express-service-readiness-middleware@1.0.16 --save

Example usage

const {  
  checkDependenciesHealth, 
  createReadinessMiddleware,
  criticalDependenciesReady,
  setLogger
} = require('express-service-readiness-middleware')
  
// if a 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 (isHealthy is optional, isReady is used if not defined)
const dependencies = [{ 
     name: 'dependency-one',
     data: { 
         connectionString: 'protocol:://{user}:{password}/test'
     },
     critical: true,
     isReady: () => Promise.resolve(true),
     isHealthy: () => Promise.resolve(true)
}]  
  
// 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:  
{
  "allDependenciesHealthy": true,
  "allCriticalDependenciesHealthy": true,  
  "dependencies": [
    {
      name": "dependency-one",
      "critical": true, 
      "data": {
        "connectionString": "protocol:://{user}:{password}/test", },
        "healthy": true
      }
    }
  ]
}  
*/

// check whether all critical dependencies are ready
const ready = criticalDependenciesReady()

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<boolean>) Indicates whether the dependency is ready
• isHealthy: (optional, Promise<boolean>) Indicates whether the dependency is healthy. isReady is used if not defined.
• 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 fall back to isReady.

const health = await checkDependenciesHealth(dependencies)

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

criticalDependenciesReady

Boolean function that can be called to determine whether all critical dependencies are ready.

const ready = criticalDependenciesReady()

stopCheckingReadiness

Stops checking whether service dependencies are ready

stopCheckingReadiness()

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
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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
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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
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SOFTWARE.