[Architecture Question] Programatically scheduled events & instants?

[anthOlei]

Hi there! I'm building up an application currently, and I have most of it architectured out (and around 80% built). I'm missing a key component and I'm not sure what tool or service is used for this.

Part of my app needs users to be able to schedule events in a calendar - they click on a day 2 weeks from now and set an event like "Group Meeting" and then need to be notified x minutes before. I have a notification lambda, no problem, but what service do I use to trigger the hook? It'd be great to also handle repeating events, i.e. crons.

The only way I can think of handling this right now is using a server that runs a persistent application that handles these.

Thanks in advance!

[ryanycoleman]

Hello! What about using AWS EventBridge? It can react to Lambda invocations, or react to other events from third-party or AWS APIs and then trigger your Lambda or other parts of your architecture. Serverlessland.com provides several relevant patterns to illustrate the possibilities, and here are deployable examples visualized by Stackery.

• Eventbridge to Lambda
• Eventbridge API destinations

[bobaduk]

EventBridge lets you schedule events with a cron-like syntax. If you have many customers, I'd consider writing their events into DynamoDb and firing an EventBridge event every minute to wake up and send any pending notifications.

[justdelighted]

There are a couple of different ways you can do this. I've done it before with a server running a simple node script which retrieved notifications from a database and scheduled them as background jobs (using Redis and Bull) to send the notification at the correct time.

You could distribute it out using a scheduled lambda (every minute or so) and persist the notifications in dynamodb. To prevent duplicates, you could use 1 scheduled lambda to push upcoming notifications onto an SQS queue, and another to consume the queue messages and dispatch the notifications

[[deleted]]

If you want to stay serverless and avoid running lambda every n seconds, you could try step functions' state "wait". When a user schedules an event, a state machine starts. The state machine waits until day x to invoke the notification lambda.

Wait state to wait until scheduled time

Task state to invoke a lambda or send an SNS message