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Monthly Downloads: 16
Programming language: Haskell
License: BSD 3-clause "New" or "Revised" License
Tags: Network     API     AWS     Amazon    

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README

About

This is a really simple system for handling queued emails. It reads emails out of a database table, and tries to send a specified number every second (well, it delays a second between each sending, so it is upper bounded by the specified number per second, but probably will be less, accounting for latency, request time, etc). It records when a message was sent. It uses the database to lock messages, so many workers can work simultaneously (but they will all try to send out the configured number of messages per second).

If messages fail to send for any reason (this could be connectivity, blacklisted addresses, etc, but NOT bounced messages, as those are sent, but come back later), the message has its failed_count incremented, and when that hits 3, we stop trying to send it. Messages are sent in plain text unless html is true, in which case they are sent as html. Right now there is no way to send both.

Software

This is designed to work with Amazon's Simple Email Service (SES), and PostgreSQL. It wouldn't be too hard to adapt it to other backends, but I wanted to keep it extremely simple, and everything I do is with PostgreSQL.

Setup

To use this, you need to create a table amazon_email_queue with the following colums:

id serial PRIMARY KEY,
to_addr text NOT NULL,
to_name text,
from_addr text NOT NULL,
from_name text NOT NULL,
subject text NOT NULL,
body text NOT NULL,
date timestamptz NOT NULL DEFAULT now(),
sent_at timestamptz,
failed_count integer NOT NULL DEFAULT 0,
html boolean NOT NULL DEFAULT false,
processing boolean NOT NULL DEFAULT false

And you should put an index on sent_at, date, failed_count, and processing (used to filter the messages). A file create.sql is provided that does this.

Then you should create a config file, which uses the configurator package, and should look like:

host = "host for postgresql"

port = 5433

user = "user for postgresql"

pass = "password for postgresql"

db = "database name"

ses-access-key = "AWS access key"

ses-secret-key = "AWS secret key"

limit = 5 -- or higher, if you have a higher rate limit

To start the mailer, pass it the path to this config file. (Note: configurator supports including other config files, and I chose the config names to overlap with the similar config file for the postgres snaplet, if you're using snap. In that case import "path/to/prod.cfg" will get you all the postgres settings).

Finally, in your application, just insert messages into the amazon_email_queue table, and then should get picked up and sent out.

Queue Cleaner

If you send a bunch of emails, eventually the queue will slow down, because even with indexes the operation to get a message from the queue slows down (if someone who knows postgres better than me knows a different sort of index that doesn't have this property, let me know!). Because of this, it makes sense to move messages out of the queue periodically. The included amazon-email-queue-cleaner executable moves messages into an amazon_email_archive table which should have a schema with a subset of the columns in the queue table, and the columns defined in a comma separated list in the config file. It will copy those columns out.

columns = "to_addr, to_name, from_addr, from_name, subject"

It is organized like this because it is often convenient to add additional application specific data to the email rows, and that data should be able to be copied to the archive. Further, there is information that isn't really important (like processing, failed_count) in the archive that is needed for the queue.

It should be run with the same parameters as the amazon-emailer executable, and will move, every minute, all sent messages to the archive table.