@byu-oit/healthcheck

Standardized web server health checks

Motivation

The Health Check Response RFC Draft for HTTP APIs establishes a standard model for health check responses. Some implementations of the RFC Draft already exist in Node.js, however, none provide a standard interface for implementing and running executors. This library aims at standardizing how Node.js developers create and run health checks within their web servers.

Terminology

An overview of the terminology used in the code base. More specific RFC Draft information can be found at: https://inadarei.github.io/rfc-healthcheck.

health check: An REST response used to determine the overall health of a web server. It contains a map of component keys and component responses. In the RFC Draft, this is also known as the Checks Object. For additional information about the information that a health check response may contain, please see the published RFC Draft.

component key: a component has a name and a metric associated with it. The name and metric make up what is known as the component key and are formatted {name}:{metric}. The metric portion of the key is optional and if omitted, the name will be the key.

component or check: a section of the health check response containing information about the status of infrastructure that the web server depends on. For more information about what a component response contains, please refer to the published RFC Draft.

executor: a function used to establish the status of a component. The returned value must be in the shape of a component response object as defined per the RFC Draft.

Installation

npm install @byu-oit/healthcheck

Usage

Fastify

Health check executors and their dependencies can be imported from external files for better code organization. For demonstration purposes, I've included all the pieces in a comprehensive example below:

// server.ts
import {HealthCheck, Status, healthCheckFastify, noopExecutorFactory} from '@byu-oit/healthcheck'
import {FastifyRequest} from 'fastify'

const healthCheck = new HealthCheck<[FastifyRequest?]>({info: {version: '1', releaseId: '1.2.2'}})
    .add('noop', 'alive', noopExecutorFactory(Status.Text.PASS))

export const app = fastify()

app.register(healthCheckFastify, {
    logLevel: 'error',
    path: '/health/details',
    healthCheck
})

Rather than calling the add function, the above example could be changed to pass in the check options in the HealthCheck constructor like so:

import {FastifyRequest, Status} from 'fastify'
import {HealthCheck} from '@byu-oit/healthcheck'

const healthCheck: HealthCheck<[FastifyRequest?]> = new HealthCheck([
    {
        name: 'noop',
        metric: 'alive',
        executor: noopExecutorFactory(Status.Text.PASS)
    }
], {info: {version: '1', releaseId: '1.2.2'}})

export const app = fastify()

app.register(healthCheckFastify, {
    logLevel: 'error',
    path: '/health/details',
    healthCheck
})

The RFC Draft allows metadata on the top level of the health check response. More information about the top-level metadata can be found on the RFC Draft website. Here is an example of passing in all the allowed top-level metadata.

const healthCheck = new HealthCheck({
    info: {
        version: "1",
        releaseId: "1.2.2",
        notes: [""],
        output: "",
        serviceId: "f03e522f-1f44-4062-9b55-9587f91c9c41",
        description: "health of authz service",
        links: {
            about: "http://api.example.com/about/authz",
            'http://api.x.io/rel/thresholds': "http://api.x.io/rel/thresholds"
        }
    }
})

Plugins

Plugins or middleware are implementations of the RFC Draft for specific web server frameworks such as fastify. Plugins must be imported directly to not bloat the required dependencies to run this package. Additionally, all plugin dependencies must be installed.

Executor Factories

Executor Factories assist in replicating common patterns for checking system statuses. like plugins, must be imported directly and require all their dependencies (if any) to be installed.

Executor	Import Path	Dependencies	Description
noopExecutorFactory	@byu-oit/healthcheck/dist/executors/noop	None	An executor for testing purposes.
fetchExecutorFactory	@byu-oit/healthcheck/dist/executors/fetch	npm install node-fetch@2	Pass in node-fetch configurations to make HTTP requests. Status Codes 2xx and 3xx will set a status of 'pass' in the health check. Any other status codes will result in a status of 'fail'.