email-failover-app

Demo simple email integration app, with failover

How it works

It's a Spring 5 non-blocking app that is configured to use two email services. It makes use of Spring Boot for simple app bootstrapping. It exposes a endpoint that can be called via HTTP POST in order to send an email. It will first attempt to use the primary configured email service provider, and if that fails it will attempt the second. If that also fails it will return with a non 2xx code.

Build and run

You'll need Gradle 4.4+ installed.

Put any API keys, domain strings into /resources/application.yaml

To build: gradle build

To run: gradle bootRun

To run tests: gradle test

Send an email

Make a HTTP POST request to /send. For example, if the server is running locally on port 8080 the full URL will be http://localhost:8080/send. The endpoint consumes a JSON object in the body.

Request body

• to: required A list of email addresses to send the email to
• cc optional A list of email addresses to send the email in cc to
• bcc optional A list of email addresses to send the email in bcc (blind carbon copy) to
• from required An email address of the sender. Replies will be directed to this address.
• subject required The email subject line
• body required The email body contents, in plain text

Example:

{
  "to": ["first@email.com", "second@email.com"],
  "cc": ["cc@email.com"],
  "from": "sender@email.com",
  "subject": "Check out this example email!",
  "body": "Not bad huh?"
}

Response

A JSON object describing the result of the transaction.

{
  "status": 200,
  "message": "Email sent successfully"
}

Response codes

• 200 OK The email was sent by a Email Service Provider successfully.
• 400 CLIENT ERROR The request was not valid, check the message in the response object for why
• 406 NOT ACCEPTABLE A field(s) in the request body does not pass validation, check the message in the response for a hint
• 500 SERVER ERROR Something went wrong in the app, and the email could not be sent

Configuration

Config lives in /resources/application.yaml.

You can edit this file to add any API keys, URLs or other configuration options. Please note a restart is required for any changes to take effect.

Improvements that could be made

• Better failover logic - at the moment it's just try primary, and if that fails try secondary.
• Potentially throttling the calls to the email service providers to prevent flooding them
• Instead of static primary/secondary email service providers configured at bootstrap, there could be a collection assigned. This would allow for more than 2 email services.
• More informative response information on what has happened, both good and bad
• Generic HTTP REST email client. They both follow a similar pattern: Map request JSON to vendor request body, and dispatch. I could use generics to abstract this further.
• Simple web page with a form for creating an email EDIT I created a simple one at /index.html, it doesn't show do much except post the form - no response apart from the console, or input validation
• Better input validation, with more informative responses