monitor

Monitor Library

A convenient library to wrap up all of the pieces needed for a Taskcluster service to record metrics and write structured logs. By default it will report any errors that cause the process to exit, and report as warnings any errors that cause stats writing to not work. To disable any of these, you can see the Options and Defaults section below.

Taskcluster has some generic concepts that are able to be monitored easily using utility functions in this package. The Usage section lists these cases and shows how to use this package to measure them.

Usage

This library is initialized early in the Node process's lifetime, while modules are still being loaded. At this time, the static method MonitorManager.register can be called to register new log message types:

import { MonitorManager } from 'taskcluster-lib-monitor';

MonitorManager.register({
  name: 'somethingHappened',
  title: 'Something Happened',
  type: 'something-happened',
  version: 1,
  level: 'info',
  description: 'A thing, it has occurred.',
  fields: {
    thing: 'The thing in question',
  },
});

Typically, message types are registered in the module where they are produced. Where multiple modules in a service produce the same message, those can be declared in src/monitor.js and that file required from src/main.js. Other Taskcluster libraries also register message types for messages that they send.

Once the service begins running, call the setup method on the monitor manager to get the "root" monitor instance. This is typically done in a loader component:

  monitor: {
    requires: ['process', 'profile', 'cfg'],
    setup: ({process, profile, cfg}) => MonitorManager.setup({
      serviceName: 'some-service',
      processName: process,
      verify: profile !== 'production',
      ...cfg.monitoring,
    }),
  },

That monitor can then be used to log, measure, count, or even create child monitors.

Typically the log references are passed to an instance of taskcluster-lib-references.

register

This library allows creating custom message types, and documents those in the service documentation. To add a message type, do the following:

MonitorManager.register({
  name: 'email',
  title: 'Email Request',
  type: 'email',
  version: 1,
  level: 'info',
  description: 'A request to send an email.',
  fields: {
    address: 'The requested recepient of the email.',
  },
});

MonitorManager.register({
  name: 'errorReport',
  title: 'Error Report',
  type: 'error-report',
  version: 1,
  level: 'any', // Notice that this is `any`
  description: 'A generic error report.',
  fields: {
    stack: 'A stack trace.',
  },
});

Given the above, the log message can be generated with

monitor.log.email({address: req.body.address});
// An example with an `any` level
monitor.log.errorReport({stack: '...'}, {level: 'warning'});

The options to register are:

• name - This will be made available on your monitor under a .log prefix.
• type - This will be the Type field of the logged message.
• version - This will end up in a v field of the Fields part of a logged message. Bump this if making a backwards-incompatible change
• level - This will be the level that this message logs at. This must either be a syslog level or any. If it is any, you must pass an object with the field level as the second argument to the logging function.
• description - A description of what this logging message means
• fields - An object where every key is the name of a required field to be logged. Corresponding values are documentation of the meaning of that field.
• serviceName - If set, then this log type appears only on this service; otherwise the log type is considered generic to all services.

If the verify option is set to true during manager setup, this library will verify that at least the required fields have been passed into the logger upon invoking it.

setup

The available options to the setup function are:

• serviceName - The name of the service
• level - A syslog logging level. Any messages with less severity than this level will not be logged.
• patchGlobal - If true (the default), any uncaught errors in the service will be reported.
• processName - If set to a string that identifies this process, cpu and memory usage of the process will be reported on an interval.
• resourceInterval - The interval (in seconds) on which to report process resources
• bailOnUnhandledRejection - If true, exit the process when an unhandled rejection occurs (the default)
• fake - If true, the monitoring object will be a fake that stores data for testing
• metadata - an object of extra fields to attach to any logs generated by this object. If one field is traceId, it is bumped to the top-level of the log.
• debug - If true, logging output will be sent to the debug log in a human-readable format
• destination - A stream to which formatted logs should be written.
• verify - If this is true, log messages that have been registered will be verified to define all of the required fields.
• errorConfig - An optional object containing a reporter field and any arguments to pass to a reporter. See below.

Error Configuration

This library supports pluggable error reporting. At the current time, the only supported plugin is SentryReporter. This will send any errors reported through monitor.reportError() (including crashes and unhandled rejections) to a sentry instance. It takes a single configration value of dsn which must be supplied.

errorConfig: {
  reporter: 'SentryReporter',
  dsn: '...',
},

Monitor objects

Monitor objects are intended to be passed around to the various things that might need to submit data for monitoring. The setup function returns a "root" monitor, and other "child" monitors can be created from the root.

To create a child monitor, call monitor.childMonitor(name, metadata). The name if given will be appended to the parent monitor's name. The metadata, if given, will be included in the fields of any logs generated by this object, in addition to the parent monitor's metadata. At least one of name and metadata must be given. The messages these child monitors produce will have a value of Logger corresponding to their full name.

Logging

A monitor instance provides the following functions:

  emerg(type, fields) // Not recommended for use
  alert(type, fields)
  crit(type, fields)
  err(type, fields)
  warning(type, fields)
  notice(type, fields)
  info(type, fields)
  debug(type, fields)

If you leave out type, the first argument will be used for fields. If fields is a string or number, we will log it in a generic message. If fields contains a traceId key, it will be moved to the top-level of the log structure. If fields contains a requestId key, it will be moved to the top-level of the log structure. This is useful for something like simple debug logging, that can be enabled in production when necessary. For example,

monitor.debug('Whatever you want to say');

results in

{Fields: {message: 'Whatever you want to say'}, ...}

Measuring and Counting Things

Note: You should prefer logging specific types rather than these generic counts and measures. They exist mostly for backwards compatibility.

To record a current measurement of a named value:

monitor.measure('foo', 10);

To increment the count of some value:

monitor.count('bar');
monitor.count('bar', 4); // increment by 4

These events will have types of monitor.measure and monitor.count respectively. The fields will have key and val.

Reporting Errors

There are lots of options for reporting errors:

// Report error as a string
monitor.reportError('Something went wrong!');
// Report error (from catch-block or something like that)
monitor.reportError(new Error("..."));
// Report an error with extra info
monitor.reportError(new Error("..."), {foo: 'bar'});
// (DEPRECATED) Report error as a warning. This will simply append 'warning' to fields
monitor.reportError(new Error("..."), 'warning');

The "extra" information is passed to the error reporting plugin and may appear there as "tags".

The Sentry error reporter will look for a sentryFingerprint property on any reported errors, and send that string to Sentry along with the default fingerprint. See the Sentry docs for details.

Monitoring CPU & Memory

// Begin monitoring CPU & Memory
const stopMonitor = monitor.resources('web');

you can later call stopMonitor() to gracefully shut down the monitoring.

Timing Functions/Promises

Often we wish to measure how long time an operation takes, synchronous or asynchronous, this can done using the monitor.timer(key, funcOrPromise) method. It takes a key (as name of the metric) and a function or promise to measure the time of. If the function returns a promise, it'll include the time it takes for the promise to resolve.

The following examples are valid usages:

// Timing a synchronous operation
const root = monitor.timer('compute-sqrt', () => {
  return Math.sqrt(25);
})
assert(root === 5);

// Timing a single asynchronous function (promise)
const task = await monitor.timer('load-task', queue.task(taskId));
assert(task.workerType == '...'); // task is the task definition response

// Timing an asynchronous function
const task = await monitor.timer('poll-for-task', async () => {
  while (true) {
    try {
      return await queue.task(taskId);
    } catch (err) {
      // Ignore error and try again
      // In the real would you want a maximum time before you stop polling
      // And probably some sleeping between each polling attempt...
    }
  }
});
assert(task.workerType == '...'); // task is the task definition response

Rejected promises and errors will bubble up, and the time be will measured and recoded just like successful functions or promises.

Timing Handlers

A common pattern in Taskcluster projects is to have handler functions in a worker that take a message as an argument and perform some action. These can be timed (in milliseconds) by wrapping them with taskcluster-lib-monitor:

const handler = function(message) {
  console.log(message);
};

const consumer = libPulse.consume({..},
  monitor.timedHandler('pulse-listener', handler));

Specifically, timedHandler takes a function and wraps it with timing logic, returning a function with the same signature.

Timing Arbitary Steps

If none of the above options are convenient for you, you can also just start and stop timers whenever you want. A timer may only be started and measured once. Any attempts over that will cause it to throw an Error.

const doodad = monitor.timeKeeper('metricName', {optional: 'extra data'});
// Do some stuff here that takes some amount of time
// ...
// Keep doing stuff here however long you like
doodad.measure();

Monitoring One-Shot Processes

Many Taskcluster services use one-shot processes to expire old data. The expectation is that these processes will be started at specific times, do their business, and exit. The oneShot method is designed to wrap such processs with timing and error handling support.

  'expire-info': {
    requires: ['cfg', 'monitor'],
    setup: ({cfg, monitor}) => {
      return monitor.oneShot('expire-info', () => {
        // do the expiration stuff
      });
    },
  },

This function will:

• time the invocation, measured as duration
• count the invocation if successful, measured as done
• report any errors or promise rejections
• shut down and flush monitoring
• call process.exit on success or failure Note, then, that the function does not return.

Testing

If the fake option is true, then all messges logged are available from the messages property on the MonitorManager, in the format {Type, Fields, Logger, Severity}. Setting this up is generally handled by the Testing library's withMonitor method.

The accumulated messages can be cleared with the reset() method. This allows tests to assert that a message was logged correctly:

assert.deepEqual(helper.monitor.messages.find(({Type}) => Type === 'task-claimed'), {
  Type: 'task-claimed',
  Fields: {...}
});

Level Configuration

If you set the level during setup to a single valid syslog level, it will be propagated to all child loggers. If you would like more control, you can use a specifically formatted string:

LEVEL='root:info api:debug handler:warning'

When you use this format, you specify a prefix without root included and after a : you specify a valid syslog level. You must set a value for root in these cases and any unspecified prefixes will default to that.

Mesage Format

This library writes logs to stdout in the mozlog format.

We add an extra message field to the top level if any of the contents of Fields are message or stack. This is for compatibility with the logging tools we use. We will add configurable output formats later if wanted.

We have both a Severity and severity field to support both our logging tooling requiremtents and mozlog's. The lowercase property reports in a string version of severity and uppercase is the syslog number for each level.

We also add a serviceContext which is used in our tooling. This contains a single field with the name of the service, and the version.

The result looks like this:

{
  "Timestamp": <time since unix epoch in nanoseconds>,
  "Type": "...",
  "Logger": "...",
  "message": "...",
  "serviceContext": {"service": "..."},
  "Hostname": "...",
  "EnvVersion": "2.0",
  "Severity": ...,
  "severity": ...,
  "Pid": ...,
  "Fields": {...}
}

The type will be set in the event object as the Type field in the mozlog format. Everything in fields will be set in the Fields. We default to info logging level so normally debug logs will not be logged.