Users need to be able to subscribe to notifications about the changes in flight information. Leveraging and building upon the designs of the web-api and airline-application we can use cloud services provided by AWS to handle our notification mechanism.
The web api will expose a subscribe enpoint which will allow the users get notifications for flights they are interested in. The subscriptions will be saved in the dynamo db as a new table to keep track of what flights users are interested in.
A dynamo db trigger will be set up on the flights table, this trigger will invoke a Lambda which will publish a message with the change to the aws topic.
AWS SNS will be responsible for sending the Push notifications. If we need to introduce other means of notifications like email or sms we can implement a fan out pattern using SNS to achieve this.
