maintenance-bot/modules/checkers/health-checker.js

import getLogger from "../../libs/logger.js"
import settings  from "../../libs/settings.js"
import https     from "https"

const log = getLogger("Health Checker", settings.checkers["health-checker"].color)

// This function is a mess -- I know.
function checkService(serviceDomain) {
    log(`Checking service '${serviceDomain}'`)
    return new Promise(
        (resolve, reject) => {
            const req = https.request({
                hostname: serviceDomain,
                port:     443,
                path:     "/",
                method:   "GET"
            }, res => {
                res.on("error", () => reject())
                res.on("end",   () => res.statusCode === 200 ? resolve() : reject())
                res.on("close", () => res.statusCode === 200 ? resolve() : reject())
                return res.statusCode === 200 ? resolve() : reject()
            })
            req.on("error", () => reject())
            req.end()
        }
    )
}

export function start(sendMessage) {
    log("Starting up the health checker...")
    log("Services to watch:", settings.checkers["health-checker"].services)

    function checkServices(serviceDomains) {
        for (const serviceDomain of serviceDomains) {
            checkService(serviceDomain).then(
                () => log(`Service '${serviceDomain}' seems to be running!`)
            ).catch(
                () => {
                    const message = `**IMPORTANT!** Service '${serviceDomain}' seems to have stopped!`
                    log(message)
                    sendMessage(message)
                }
            )
        }
    }

    checkServices(settings.checkers["health-checker"].services)

    setInterval(
        () => checkServices(settings.checkers["health-checker"].services),
        (settings.checkers["health-checker"].interval ?? 300) * 1000
    )

    return
}