Tutorial: 8-Interfaces

Interfaces are tools you can use to improve your process management.

For the following examples, you can use a basic task.js:

// task.js
var ipc = process.relieve.ipc

module.exports = {
  start: function() {
    ipc.on('ping', function() {
      ipc.send('pong')
    })

    setInterval(e => {
      console.log('Still alive')
    }, 1000)
  }
}

Logs

For example, you may want to set up relieve-logger to output logs in a file and handle log rotation out of the box:

npm install relieve-logger --save #you should have relieve already

// worker.js
var Logger = require('relieve-logger')
var ScriptTask = require('relieve/tasks/ScriptTask')

var logger = new Logger(`logs/out.log`, `logs/err.log`, {delay: '1d'}) // creates a logger that rotates files every day

var task = new ScriptTask('task.js', {
  interfaces: [logger]
})

Yes, that's all you need to do so that task.js outputs its logs in logs/out|err.log with file rotation!

FailSafe

Now, with relieve, we're in a world where there is a Worker (Master) and one or more Tasks (Child). You may be wondering what happens to your Task if the Worker exits. Well, as we use IPC by default, and that the child process is not detached, the Task will also die.

This may be a problem, especially if the Task is way more important then the worker. Usually the worker is only there to manage the tasks, and the task should have no trouble working without the worker.

For this to work, let me introduce the FailSafe interface. Instead of using the IPC protocol, it transparently replaces it by a TCP protocol having the same API.

First let's install the FailSafe interface:

npm install relieve-failsafe --save

To use this, simply add the interface:

// worker.js
var CallableTask = require('relieve/tasks/ScriptTask')
var FailSafe = require('relieve-failsafe')

var task = new ScriptTask('task.js', {
  interfaces: [new FailSafe()]
})

task.start()
.then(() => {
  task.on('pong', () => console.log('got pong'))

  task.call('ping')
})

Now launch the worker.js script, your task is up. Kill the worker, the task is still up. Restart the worker, it'll re-attach the task.

But wait, how do I kill my task now?

Just use task.stop() from the worker:

task.stop()

Combine everything

A more complex example sets up a full-featured task with automatic logging, master-independent and a method to get usage data:

var CallableTask = require('relieve/tasks/ScriptTask')
var Logger = require('relieve-logger')
var FailSafe = require('relieve-failsafe')
var monitorContainer = require.resolve('relieve/containers/MonitorContainer')

var logger = new Logger('out.log', 'err.log')
var failSafety = new FailSafe()

var t = new CallableTask(task.script, {
  interfaces: [logger, failSafety],
  childprocess: {
    env: {
      SOME_ENV_VARIABLE: 'foobar'
    }
  },
  containers: [monitorContainer],
  restart: true
})