ostrio:mailer

v2.4.0Published 4 months ago

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MailTime

Micro-service package for mail queue, with Server and Client API. Build on top of nodemailer package.

Every MailTime instance can be configured to be a Server or Client.

Main difference of Server from Client - Server handles queue and actually sends email. While Client is only put emails into the queue.

"Mail-Time" is a micro-service package for mail queue, with Server and Client APIs. Build on top of the nodemailer package.

Every MailTime instance can get configured as Server or Client.

The main difference between Server and Client modes is that the Server handles the queue and sends email. While the Client only adds emails into the queue.

ToC

Main features:

  • 👨‍🔬 ~92% tests coverage;
  • 📦 Two simple dependencies, written from scratch for top performance;
  • 🏢 Synchronize email queue across multiple servers;
  • 💪 Bulletproof design, built-in retries.

How does it work?

Redundant solution for email transmission.

Single point of failure

Issue - classic solution with a single point of failure:

|----------------|         |------|         |------------------|
|  Other mailer  | ------> | SMTP | ------> |  ^_^ Happy user  |
|----------------|         |------|         |------------------|

The scheme above will work as long as SMTP service is available
or connection between your server and SMPT is up. Once network
failure occurs or SMTP service is down - users won't be happy

|----------------|  \ /    |------|         |------------------|
|  Other mailer  | --X---> | SMTP | ------> | 0_o Disappointed |
|----------------|  / \    |------|         |------------------|
                     ^- email lost in vain

Single SMTP solution may work in case of network or other failures
As long as MailTime has not received confirmation what email is sent
it will keep the letter in the queue and retry to send it again

|----------------|    /    |------|         |------------------|
|   Mail Time    | --X---> | SMTP | ------> |  ^_^ Happy user  |
|---^------------|  /      |------|         |------^-----------|
     \-------------/ ^- We will try later         /
      \- put it back into queue                  /
       \----------Once connection is back ------/

Multiple SMTP providers

Backup scheme with multiple SMTP providers

                           |--------|
                     /--X--| SMTP 1 |
                    /   ^  |--------|
                   /    \--- Retry with next provider
|----------------|/        |--------|         |------------------|
|   Mail Time    | ---X--> | SMTP 2 |      /->|  ^_^ Happy user  |
|----------------|\   ^    |--------|     /   |------------------|
                   \  \--- Retry         /
                    \      |--------|   /
                     \---->| SMTP 3 |--/
                           |--------|

Cluster issue

It is common to create a "Cluster" of servers to balance the load and add a durability layer for horizontal scaling of quickly growing applications.

Most modern application has scheduled or recurring emails. For example, once a day — with recent news and updates. It won't be an issue with a single server setup — the server would send emails at a daily interval via timer or CRON. While in "Cluster" implementation — each server will attempt to send the same email. In such cases, users will receive multiple emails with the same content. We built MailTime to address this and other similar issues.

Here is how this issue is solved by using MailTime:

|===================THE=CLUSTER===================| |=QUEUE=| |===Mail=Time===|
| |----------|     |----------|     |----------|  | |       | |=Micro-service=|   |--------|
| |   App    |     |   App    |     |   App    |  | |       | |               |-->| SMTP 1 |------\
| | Server 1 |     | Server 2 |     | Server 3 |  | |    <--------            |   |--------|       \
| |-----\----|     |----\-----|     |----\-----|  | |    -------->            |                |-------------|
|        \---------------\----------------\---------->      | |               |   |--------|   |     ^_^     |
| Each of the "App Server" or "Cluster Node"      | |       | |               |-->| SMTP 2 |-->| Happy users |
| runs Mail Time as a Client which only puts      | |       | |               |   |--------|   |-------------|
| emails into the queue. Aside to "App Servers"   | |       | |               |                    /
| We suggest running Mail Time as a Micro-service | |       | |               |   |--------|      /
| which will be responsible for making sure queue | |       | |               |-->| SMTP 3 |-----/
| has no duplicates and to actually send emails   | |       | |               |   |--------|
|=================================================| |=======| |===============|

Features

  • Queue - Managed via MongoDB, will survive server reboots and failures
  • Support for multiple server setups - "Cluster", Phusion Passenger instances, Load Balanced solutions, etc.
  • Emails concatenation by addressee email - Reduce amount of sent emails to a single user with concatenation, and avoid mistakenly doubled emails
  • When concatenation is enabled - Same emails won't be sent twice, if for any reason, due to bad logic or application failure emails are sent twice or more times - this is solution to solve this annoying behavior
  • Balancing for multiple nodemailer's transports, two modes - backup and balancing. This is the most useful feature — allowing to reduce the cost of SMTP services and add extra layer of durability. If one transport failing to send an email mail-time will switch to the next one
  • Sending retries for network and other failures
  • Templating support with Mustache-like placeholders

Installation

To implement Server functionality — as a first step install nodemailer, although this package meant to be used with nodemailer, it's not added as the dependency, as nodemailer not needed by Client, and you're free to choose nodemailer's version to fit your project needs:

npm install --save nodemailer

Install MailTime package:

# for node@>=8.9.0
npm install --save mail-time

# for node@<8.9.0
npm install --save mail-time@=0.1.7

Basic usage

Require package:

1const MailTime = require('mail-time');

Create nodemailer's transports (see nodemailer docs):

1const transports = [];
2const nodemailer = require('nodemailer');
3
4// Use DIRECT transport
5// and enable sending email from localhost
6// install "nodemailer-direct-transport" NPM package:
7const directTransport = require('nodemailer-direct-transport');
8const directTransportOpts = {
9  pool: false,
10  direct: true,
11  name: 'mail.example.com',
12  from: 'no-reply@example.com',
13};
14transports.push(nodemailer.createTransport(directTransport(directTransportOpts)));
15// IMPORTANT: Copy-paste passed options from directTransport() to
16// transport's "options" property, to make sure it's available to MailTime package:
17transports[0].options = directTransportOpts;
18
19// Private SMTP
20transports.push(nodemailer.createTransport({
21  host: 'smtp.example.com',
22  from: 'no-reply@example.com',
23  auth: {
24    user: 'no-reply',
25    pass: 'xxx'
26  },
27}));
28
29// Google Apps SMTP
30transports.push(nodemailer.createTransport({
31  host: 'smtp.gmail.com',
32  from: 'no-reply@mail.example.com',
33  auth: {
34    user: 'no-reply@mail.example.com',
35    pass: 'xxx'
36  },
37}));
38
39// Mailing service (SparkPost as example)
40transports.push(nodemailer.createTransport({
41  host: 'smtp.sparkpostmail.com',
42  port: 587,
43  from: 'no-reply@mail2.example.com',
44  auth: {
45    user: 'SMTP_Injection',
46    pass: 'xxx'
47  },
48}));

As the next step initiate mail-time in the Server mode, it will be able to send and add emails to the queue. Connecting to a MongoDB before initiating new MailTime instance:

1const MongoClient = require('mongodb').MongoClient;
2const MailTime    = require('mail-time');
3const dbName      = 'DatabaseName';
4
5// We're using environment variable MONGO_URL
6// to store connection string to MongoDB
7// example: "MONGO_URL=mongodb://127.0.0.1:27017/myapp node mail-micro-service.js"
8MongoClient.connect(process.env.MONGO_URL, (error, client) => {
9  const db = client.db(dbName);
10
11  const mailQueue = new MailTime({
12    db, // MongoDB
13    type: 'server',
14    strategy: 'balancer', // Transports will be used in round robin chain
15    transports,
16    from(transport) {
17      // To pass spam-filters `from` field should be correctly set
18      // for each transport, check `transport` object for more options
19      return `"Awesome App" <${transport.options.from}>`;
20    },
21    concatEmails: true, // Concatenate emails to the same addressee
22    concatDelimiter: '<h1>{{{subject}}}</h1>', // Start each concatenated email with it's own subject
23    template: MailTime.Template // Use default template
24  });
25});

Only one MailTime Server instance required to send email. In the other parts of an app (like UI units or in sub-apps) use mail-time in the Client mode to add emails to queue:

1const MongoClient = require('mongodb').MongoClient;
2const MailTime    = require('mail-time');
3const dbName      = 'DatabaseName';
4
5MongoClient.connect(process.env.MONGO_URL, (error, client) => {
6  const db = client.db(dbName);
7
8  const mailQueue = new MailTime({
9    db,
10    type: 'client',
11    strategy: 'balancer', // Transports will be used in round robin chain
12    concatEmails: true // Concatenate emails to the same address
13  });
14});

Send email example:

1mailQueue.sendMail({
2  to: 'user@gmail.com',
3  subject: 'You\'ve got an email!',
4  text: 'Plain text message',
5  html: '<h1>HTML</h1><p>Styled message</p>'
6});

Two MailTime instances usage example

Create two MailTime instances with different settings.

1// USE FOR NON-URGENT EMAILS WHICH IS OKAY TO CONCATENATE
2const mailQueue = new MailTime({
3  db: db,
4  interval: 35,
5  strategy: 'backup',
6  failsToNext: 1,
7  concatEmails: true,
8  concatThrottling: 16,
9  zombieTime: 120000
10});
11
12// USE FOR TRANSACTIONAL EMAILS AND ALERTS
13const mailInstantQueue = new MailTime({
14  db: db,
15  prefix: 'instant',
16  interval: 2,
17  strategy: 'backup',
18  failsToNext: 1,
19  concatEmails: false,
20  zombieTime: 20000
21});
22
23mailQueue.sendMail({
24  to: 'user@gmail.com',
25  subject: 'You\'ve got an email!',
26  text: 'Plain text message',
27  html: '<h1>HTML</h1><p>Styled message</p>'
28});
29
30mailInstantQueue.sendMail({
31  to: 'user@gmail.com',
32  subject: 'Sign in request',
33  text: 'Your OTP login code: xxxx:',
34  html: '<h1>Code:</h1><code>XXXX</code>'
35});

Passing variables to the template

All options passed to the .sendMail() method is available inside text, html, and global templates

1const templates = {
2  global: '<html xmlns="http://www.w3.org/1999/xhtml"><head><title>{{subject}}</title></head><body>{{html}}<footer>Message sent to @{{username}} user ({{to}})</footer></body></html>',
3  signInCode: {
4    text: 'Hello @{{username}}! Here\'s your login code: {{code}}'
5    html: `<h1>Sign-in request</h1><p>Hello @{{username}}! Copy your login code below <pre><code>{{code}}</code></pre>`
6  }
7}
8
9const mailQueue = new MailTime({
10  db: db,
11  template: templates.global
12});
13
14mailQueue.sendMail({
15  to: 'user@gmail.com',
16  subject: 'Sign-in request',
17  username: 'johndoe',
18  code: 'XXXXX-YY'
19  text: templates.signInCode.text,
20  html: templates.signInCode.html
21});

Meteor.js usage:

Mail-Time package can be installed and used within Meteor.js via NPM or Atmosphere

Installation & Import (via NPM):

Install NPM mail-time package:

meteor npm install --save mail-time

Meteor.js: ES6 Import NPM package:

1import MailTime from 'mail-time';

Installation & Import (via Atmosphere):

Install Atmosphere ostrio:mailer package:

meteor add ostrio:mailer

Meteor.js: ES6 Import atmosphere package:

1import MailTime from 'meteor/ostrio:mailer';

Usage:

mail-time package usage examples in Meteor.js

1import { MongoInternals } from 'meteor/mongo';
2
3import MailTime from 'mail-time';
4import nodemailer from 'nodemailer';
5// Use DIRECT transport
6// To enable sending email from localhost
7// install "nodemailer-direct-transport" NPM package:
8import directTransport from 'nodemailer-direct-transport';
9
10const transports = [];
11const directTransportOpts = {
12  pool: false,
13  direct: true,
14  name: 'mail.example.com',
15  from: 'no-reply@example.com',
16};
17transports.push(nodemailer.createTransport(directTransport(directTransportOpts)));
18// IMPORTANT: Copy-paste passed options from directTransport() to
19// transport's "options" property, to make sure it's available to MailTime package:
20transports[0].options = directTransportOpts;
21
22////////////////////////
23// For more transports example see sections above and read nodemailer's docs
24////////////////////////
25
26const mailQueue = new MailTime({
27  db: MongoInternals.defaultRemoteCollectionDriver().mongo.db, // MongoDB
28  transports,
29  from(transport) {
30    // To pass spam-filters `from` field should be correctly set
31    // for each transport, check `transport` object for more options
32    return '"Awesome App" <' + transport.options.from + '>';
33  }
34});

API

All available constructor options and .sendMail() method API overview

new MailTime(opts) constructor

  • opts {Object} - Configuration object
  • opts.db {Db} - [Required] Mongo's Db instance. For example returned in callback of MongoClient.connect()
  • opts.type {String} - [Optional] client or server, default - server
  • opts.from {Function} - [Optional] A function which returns String of from field, format: "MyApp" <user@example.com>
  • opts.transports {Array} - [Optional] An array of nodemailer's transports, returned from nodemailer.createTransport({})
  • opts.strategy {String} - [Optional] backup or balancer, default - backup. If set to backup, first transport will be used unless failed to send failsToNext times. If set to balancer - transports will be used equally in round robin chain
  • opts.failsToNext {Number} - [Optional] After how many failed "send attempts" switch to next transport, applied only for backup strategy, default - 4
  • opts.prefix {String} - [Optional] Use unique prefixes to create multiple MailTime instances on same MongoDB
  • opts.maxTries {Number} - [Optional] How many times resend failed emails, default - 60
  • opts.interval {Number} - [Optional] Interval in seconds between send re-tries, default - 60
  • opts.zombieTime {Number} - [Optional] Time in milliseconds, after this period - pending email will be interpreted as "zombie". This parameter allows to rescue pending email from "zombie mode" in case when: server was rebooted, exception during runtime was thrown, or caused by bad logic, default - 32786. This option is used by package itself and passed directly to JoSk package
  • opts.keepHistory {Boolean} - [Optional] By default sent emails not stored in the database. Set { keepHistory: true } to keep queue task as it is in the database, default - false
  • opts.concatEmails {Boolean} - [Optional] Concatenate email by to field, default - false
  • opts.concatSubject {String} - [Optional] Email subject used in concatenated email, default - Multiple notifications
  • opts.concatDelimiter {String} - [Optional] HTML or plain string delimiter used between concatenated email, default - <hr>
  • opts.concatThrottling {Number} - [Optional] Time in seconds while emails are waiting to be concatenated, default - 60
  • opts.revolvingInterval {Number} - [Optional] Interval in milliseconds in between queue checks, default - 256. Recommended value — between opts.minRevolvingDelay and opts.maxRevolvingDelay
  • opts.minRevolvingDelay {Number} - [Optional] Minimum revolving delay — the minimum delay between tasks executions in milliseconds, default - 64. This option is passed directly to JoSk package
  • opts.maxRevolvingDelay {Number} - [Optional] Maximum revolving delay — the maximum delay between tasks executions in milliseconds, default - 256. This option is passed directly to JoSk package
  • opts.template {String} - [Optional] Mustache-like template, default - {{{html}}}, all options passed to sendMail is available in Template, like to, subject, text, html or any other custom option. Use {{opt}} for string placeholders and {{{opt}}} for html placeholders

sendMail(opts [, callback])

  • Alias - send()
  • opts {Object} - Configuration object
  • opts.sendAt {Date} - When email should be sent, default - new Date() use with caution on multi-server setup at different location with the different time-zones
  • opts.template - Email specific template, this will override default template passed to MailTime constructor
  • opts.concatSubject - Email specific concatenation subject, this will override default concatenation subject passed to MailTime constructor
  • opts[key] {Mix} - Other custom and NodeMailer specific options, like text, html and to, see more here. Note attachments should work only via path, and file must exists on all micro-services servers
  • callback {Function} - Callback called after the email was sent or failed to be sent. Do not use on multi-server setup

static MailTime.Template

Simple and bulletproof HTML template, see its source. Usage example:

1const MailTime  = require('mail-time');
2// Make it default
3const mailQueue = new MailTime({
4  db: db, // MongoDB
5  /* .. */
6  template: MailTime.Template
7});
8
9// For single letter
10mailQueue.sendMail({
11  to: 'user@gmail.com',
12  /* .. */
13  template: MailTime.Template
14});

Template Example

Pass custom template via template property to .sendMail() method

1mailQueue.sendMail({
2  to: 'user@gmail.com',
3  userName: 'Mike',
4  subject: 'Sign up confirmation',
5  text: 'Hello {{userName}}, \r\n Thank you for registration \r\n Your login: {{to}}',
6  html: '<div style="text-align: center"><h1>Hello {{userName}}</h1><p><ul><li>Thank you for registration</li><li>Your login: {{to}}</li></ul></p></div>',
7  template: '<body>{{{html}}}</body>'
8});

Testing

  1. Clone this package
  2. In Terminal (Console) go to directory where package is cloned
  3. Then run:

Test NPM package:

# Before run tests make sure NODE_ENV === development
# Install NPM dependencies
npm install --save-dev

# Before run tests you need to have running MongoDB
DEBUG="true" EMAIL_DOMAIN="example.com" MONGO_URL="mongodb://127.0.0.1:27017/npm-mail-time-test-001" npm test

# Be patient, tests are taking around 2 mins

Test Atmosphere (meteor.js) package:

# Default
EMAIL_DOMAIN="example.com" meteor test-packages ./ --driver-package=meteortesting:mocha

# With custom port
DEBUG="true" EMAIL_DOMAIN="example.com" meteor test-packages ./ --driver-package=meteortesting:mocha --port 8888

# With local MongoDB and custom port
DEBUG="true" EMAIL_DOMAIN="example.com" MONGO_URL="mongodb://127.0.0.1:27017/meteor-mail-time-test-001" meteor test-packages ./ --driver-package=meteortesting:mocha --port 8888

# Be patient, tests are taking around 2 mins

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