To run the microservice

• git clone ...
• cd mailing-microservice
• npm run install
• cp .env.example .env
• vim .env
• Fill in the value of the environment
• npm run dev OR if have pm2 installed globally then run pm2 start server.ts

Microservice archtiecture

• This microservice following message Queue principle

• We have two sources of the emails -- 1.APIs --.Events

• The above two email sources will add the email content( body, recipients) into the queue, and a message will be populated to the end user tells him that system is processing his email.

Notes

- We have one Consumer running all the time to check the email Queue and deal with them.

- The consumer will check every 2 seconds on the queue

- If got any email, will pull it and update it's status to be under processingstatus, and after sending the email the status will be updated to be one of [SENT, FAILED] depending on the email delivery gateway response.

- We have added some logic to ensure that we have a fixed gap between each sending email processes.

- Regardless the taken time of sending the email (becuase it's not a fixed time, it depends on many factors like [internet connetion, mail delivery service, etc...]) we have a fixed gap between calls,

- We have accomplished the fixed gap by adding setTimeout where we call the recursion.

- The microservice has been tested using this library https://www.npmjs.com/package/loadtest and the result has been attached below.

- We can increase the speed of the microservice by decreasing the gap between the mail delivery API calls, and by pulling more than 1 email from the queue

the attached chart will explain the steps.

Scalability

We have increased the availability of the app by running it on all EC2 processors using pm2 start server.ts -i -1

and in my EC2 case the app will be cloned 2 times

Things to Do:

Build UI using React to submit a new email (submit the recipients and email body)

Build UI to show the progress, How many remaning emails in the queue and so on