const metrics = require('@overleaf/metrics') const logger = require('logger-sharelatex') const os = require('os') const HOST = os.hostname() const PID = process.pid let COUNT = 0 const CHANNEL_MANAGER = {} // hash of event checkers by channel name const CHANNEL_ERROR = {} // error status by channel name module.exports = class HealthCheckManager { // create an instance of this class which checks that an event with a unique // id is received only once within a timeout constructor(channel, timeout) { // unique event string this.channel = channel this.id = `host=${HOST}:pid=${PID}:count=${COUNT++}` // count of number of times the event is received this.count = 0 // after a timeout check the status of the count this.handler = setTimeout(() => { this.setStatus() }, timeout || 1000) // use a timer to record the latency of the channel this.timer = new metrics.Timer(`event.${this.channel}.latency`) // keep a record of these objects to dispatch on CHANNEL_MANAGER[this.channel] = this } processEvent(id) { // if this is our event record it if (id === this.id) { this.count++ if (this.timer) { this.timer.done() } this.timer = undefined // only time the latency of the first event } } setStatus() { // if we saw the event anything other than a single time that is an error const isFailing = this.count !== 1 if (isFailing) { logger.err( { channel: this.channel, count: this.count, id: this.id }, 'redis channel health check error' ) } CHANNEL_ERROR[this.channel] = isFailing } // class methods static check(channel, id) { // dispatch event to manager for channel if (CHANNEL_MANAGER[channel]) { CHANNEL_MANAGER[channel].processEvent(id) } } static status() { // return status of all channels for logging return CHANNEL_ERROR } static isFailing() { // check if any channel status is bad for (const channel in CHANNEL_ERROR) { const error = CHANNEL_ERROR[channel] if (error === true) { return true } } return false } }