@mojaloop/central-services-shared/src/healthCheck/HealthCheck.js

Shared code for mojaloop central services

/*****
 License
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 Names of the original copyright holders (individuals or organizations)
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 ******/

'use strict'

const {
  statusEnum
} = require('./HealthCheckEnums')
const Logger = require('@mojaloop/central-services-logger')

/**
 * @class HealthCheck
 *
 *
 * HealthCheck is a common class for handling health checks across multiple projects. If you wish to test
 * subservices as part of your health check, create a new HealthCheck, and pass in an array of serviceChecks.
 *
 * @example
 * //Construct a new HealthCheck, and pass through a package.json, and List of ServiceCheckerFuncs
 *
 * const packageJson = require('../package.json')
 * const serviceChecks = [
 *   //Implement these methods
 *   () => Promise.resolve({status: statusEnum.OK, service: serviceName.datastore }),
 *   () => Promise.resolve({status: statusEnum.OK, service: serviceName.broker }),
 * ]
 * const healthCheck = new HealthCheck(packageJson, serviceChecks)
 * const health = await healthCheck.getHealth()
 *
 */
class HealthCheck {
  /**
   * SubServiceHealth
   * @typedef SubServiceHealth An object describing the health of a sub-service
   * @property {StatusEnum} status The status of the service. See HealthCheckEnums.js
   * @property {ServiceName} service The name of the service. See HealthCheckEnums.js
   */

  /**
   * A function that checks the health of a service
   * @typedef {ServiceCheckerFunc} ServiceCheckerFunc
   * @returns {Promise<SubServiceHealth>} SubService health check object
   *
   * @example
   * () => {
   *   return Promise.resolve({status: statusEnum.OK, service: serviceName.datastore })
   * }
   */

  /**
   * @function constructor
   *
   * @param {object} packageJson A standard package.json file
   * @param {object.version} version The version code of the package.json file
   * @param {ServiceCheckerFunc[]} serviceChecks An array of ServiceCheckerFunctions
   */
  constructor (packageJson, serviceChecks) {
    this.packageJson = packageJson
    this.serviceChecks = serviceChecks

    this.getHealth = this.getHealth.bind(this)
  }

  /**
   * @function getHealth
   *
   * @description Gets the health of the service along with sub-services
   *
   */
  async getHealth (context = undefined) {
    // Default values
    let status = statusEnum.OK
    let isHealthy = true
    let subServices = {}

    const uptime = process.uptime() // in seconds by default
    const startTimeDate = new Date(Date.now() - uptime)
    const startTime = startTimeDate.toISOString()
    const versionNumber = this.packageJson.version

    try {
      const services = await Promise.all(this.serviceChecks.map(s => s(context)))
      isHealthy = HealthCheck.evaluateServiceHealth(services)
      subServices = {
        services
      }
    } catch (err) {
      Logger.isErrorEnabled && Logger.error(`HealthCheck.getSubServiceHealth failed with error: ${err.message}`)
      isHealthy = false
    }

    if (!isHealthy) {
      status = statusEnum.DOWN
    }

    return {
      status,
      uptime,
      startTime,
      versionNumber,
      ...subServices
    }
  }

  /**
   * @function evaluateServiceHealth
   *
   * @description
   * Evaluate the health based on the SubService health array
   * if any service.status is DOWN, then the entire service
   * is considered unhealthy (will return false)
   *
   * @param {Array<Service>} services - A list of the services to evaluate
   *
   */
  static evaluateServiceHealth (services) {
    return services.reduce((acc, curr) => {
      if (!acc) {
        return acc
      }
      if (curr.status === statusEnum.DOWN) {
        return false
      }

      return acc
    }, true)
  }
}

module.exports = HealthCheck