EventBridge

“EventBridge is a serverless service that uses events to connect application components together.” Most AWS services dispatch events in different situations. For instance, ECS dispatches an event when a task starts and Batch dispatches an event when a job succeeds or fails. With EventBridge, we can react to these events and build what they call an Event-driven architecture: a system that generates and reacts to certain events. For instance, we can invoke a Lambda function when a Batch job fails.

But besides events generated from AWS services, we can also create our own events that happen on a pre-defined schedule:

  • an event that happens every hour at the 15 minutes of the clock (1:15, 2:15, …)
  • and event that happens every Friday at midnight
  • …

These events, just like the events emitted from AWS services, can be hooked up to a Lambda function. Therefore, we can run our Lambda function automatically based on a schedule. The most popular type of defining a schedule is via cron expressions. cron is a tool available on Unix-based systems that enable users to schedule a job. It has a certain format that must be followed:

<minute> <hour> <day-of-month> <month> <day-of-week>

The cron format on AWS, however, has an extra field at the end that defines the year:

<minute> <hour> <day-of-month> <month> <day-of-week> <year>

Explaining the cron syntax is not what this post is about. You can play around with it here, though.

Shedule a Lambda Function with EventBridge using Terraform

Here, we create a Lambda function and have EventBridge invoke it every 5 minutes: