PowerShell SMTP server for Elastic Beanstalk

Applications developed in .net commonly send email by creating mime files (.eml files) and dropping them into a specified folder.  The actual sending often depends on Microsoft's IIS 6 SMTP server.

SMTP server replacement in Elastic Beanstalk

When such applications get migrated to Elastic Beanstalk (EB), every instance of the application runs on it's own instance (server).  Any functionality that rights locally, writes to the local storage of that instance, which can be replaced at any time.  Each instance also has to have it's own SMTP server installation, and IIS 6 can't be easily scripted.

An alternative method is therefore required to pick up .eml files generated and emailing them.  Ideally, the applications should be changed, but as this is not always practical, I created a solution to schedule a task to regularly run a PowerShell script.  The script checks for files in a location (dropmail folder), and processes them.

The simplest way to make changes to Elastic Beanstalk instances is through “.config” files in the .ebextensions folder.  A file “schedulemail.config” is created in the .ebextensions folder.

The solution is a simple way that illustrates a number of things, including the use of ebextensions with Windows Elastic Beanstalk applications, scheduling tasks with PowerShell, and sending .eml files with PowerShell (more later).

The .config files you create in .ebextensions are YAML files.  The key things to know about these files are:

• indentation is critical (think Python)
• you can't use tabs, only spaces
• elastic beanstalk applications simply fail if there's anything wrong.

I have found that the most common reason for a simple, silent, failure of an EB deployment is a tab in a .config file.

This config file creates three files:
c:/software/sendFile.ps1
c:/software/archiveEmail.ps1
c:/software/scheduleMail.ps1

It then runs the last of these as a command.  This creates a scheduled task that runs sendFile.ps1 every minute and archiveEmail.ps1 every 10 minutes.

Emails are archived to an S3 bucket, where a lifecycle rule can be set up to delete anything older than 2 weeks, but that can be modified as required.  Of course, whether or not it is necessary to archive the email files would depend entirely on your application.

The actual sendFile.ps1 in this file sends email using Mandrill, but on the way there I also used two other methods for sending .eml files.  Any of them can very easily be substituted.

The config file can be downloaded from my github repository and modified.  You will have to add your own key, and if you want to receive notification in the event of failure, add your own email.