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  
  
```js  
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<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 fallback to isReady.

const health = await checkDependenciesHealth(dependencies)  

License

(MIT)

Copyright (c) 2023 Lee Crowe

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