monitor.js

module.exports = class {
	constructor(
		monitor,
		logger,
		instrumentation,
		metric,
		healthCheck,
		container,
		healthCheckMetric
	) {
		this.container = container;
		this.monitor = monitor;
		this.logger = logger;
		this.metric = instrumentation.metric(metric);
		this.healthCheck = healthCheck;
		this.config = [];
		this.healthCheckMetric = instrumentation.metric(healthCheckMetric);
	}

	register({ serviceId, prop, type, name, isRequired, isInitiallyConnected }) {
		if (type && !this.monitor[type]) {
			throw new Error(`Could not find monitor method to handle type ${type}`);
		}

		this.config.push({
			serviceId,
			prop,
			type,
			name,
			isRequired,
			isInitiallyConnected,
		});
	}

	start() {
		return new Promise((resolve, reject) => {
			this.config.map((c) => {
				let monitored = this.container.get(c.serviceId);

				if (c.prop) {
					monitored = monitored[c.prop];
				}

				if (!monitored) {
					return reject(
						new Error(
							`Could not resolve prop ${c.prop} for component ${c.serviceId}`
						)
					);
				}

				let monitorMethod = c.type;

				if (!monitorMethod) {
					monitorMethod = "on";
				}

				let probe = this.monitor[monitorMethod](monitored).as(c.name);

				if (c.isRequired) {
					probe.required();
				}

				if (c.isInitiallyConnected) {
					probe.initiallyConnected();
				}
			});

			this.monitor.probes.map((p) => {
				p.on("connected", () => {
					this.logger.info({ probe: p.name }, `${p.name} connected.`);
					this.metric.set({ probe: p.name }, 1);

					this.healthCheckMetric.set(
						{ healthcheck_name: p.name, healthcheck_result: "unhealthy" },
						0
					);
					this.healthCheckMetric.set(
						{ healthcheck_name: p.name, healthcheck_result: "degraded" },
						0
					);
					this.healthCheckMetric.set(
						{ healthcheck_name: p.name, healthcheck_result: "healthy" },
						1
					);
				});
				p.on("disconnected", (event) => {
					let reason = event ? event.message : "";
					this.logger.info(
						{ probe: p.name, reason },
						`${p.name} disconnected.`
					);
					this.metric.set({ probe: p.name }, 0);

					if (p.isRequired) {
						this.healthCheckMetric.set(
							{ healthcheck_name: p.name, healthcheck_result: "unhealthy" },
							1
						);
						this.healthCheckMetric.set(
							{ healthcheck_name: p.name, healthcheck_result: "degraded" },
							0
						);
						this.healthCheckMetric.set(
							{ healthcheck_name: p.name, healthcheck_result: "healthy" },
							0
						);
					} else {
						this.healthCheckMetric.set(
							{ healthcheck_name: p.name, healthcheck_result: "unhealthy" },
							0
						);
						this.healthCheckMetric.set(
							{ healthcheck_name: p.name, healthcheck_result: "degraded" },
							1
						);
						this.healthCheckMetric.set(
							{ healthcheck_name: p.name, healthcheck_result: "healthy" },
							0
						);
					}
				});

				this.healthCheck.addCheck(p.name, (r) => {
					let reason = p.details && p.details.message ? p.details.message : "";
					if (!p.connected && p.isRequired) {
						r.unhealthy(
							reason || `${p.name} disconnected.`,
							`check ${p.name}.`,
							`${p.name} unavailable.`
						);
					} else if (!p.connected) {
						r.degraded(reason || `${p.name} disconnected.`, `check ${p.name}.`);
					} else {
						r.healthy(`${p.name} connected.`);
					}
				});
				p.init();
			});

			resolve();
		});
	}
};