Overview
This article explains how to use AWS EventBridge to schedule Lambda functions for periodic execution.
I used this approach to implement scheduled reminder notifications for a LINE Bot. For example, you can send cleaning reminders every morning at 7 AM without managing any servers.
What is AWS EventBridge?
AWS EventBridge is a service that facilitates event passing between AWS services. It has two main use cases:
| Use Case | Description |
|---|---|
| Scheduled Execution | Run Lambda periodically using cron or rate expressions |
| Event-Driven | Trigger Lambda on events like S3 file uploads |
This article focuses on scheduled execution.
Real-World Use Cases
EventBridge + Lambda scheduled execution is useful for:
- Reminder notifications: Send daily notifications to Slack or LINE at fixed times
- Batch processing: Aggregate data hourly and save to database
- Health checks: Monitor external API availability every 5 minutes
- Cleanup tasks: Delete old logs every night
I use this for my Cleaning Reminder Bot to check notification conditions every hour.
Prerequisites
This guide assumes you have already created a Lambda function. For instructions on creating Lambda functions, see the AWS Lambda Getting Started guide.
Steps
1. Add a Trigger
Select the Lambda function you want to schedule with EventBridge and click “Add trigger”.
2. Select EventBridge
Choose “EventBridge (CloudWatch Events)” from the trigger options.
3. Configure the Schedule
After selecting EventBridge, you’ll be prompted to create a rule. Configure the schedule as needed.
4. Setup Complete
Once configured, EventBridge will appear as a trigger in the Lambda function diagram.
Cron Expression Syntax
EventBridge cron expressions consist of 6 fields:
| |
Common Patterns
| Timing | Cron Expression |
|---|---|
| Daily at 9 AM (UTC) | cron(0 9 * * ? *) |
| Daily at 9 AM (JST = UTC+9) | cron(0 0 * * ? *) |
| Every hour at minute 0 | cron(0 * * * ? *) |
| Every 5 minutes | cron(0/5 * * * ? *) |
| Weekdays only at 9 AM (UTC) | cron(0 9 ? * MON-FRI *) |
| First day of each month at midnight (UTC) | cron(0 0 1 * ? *) |
Note: Timezone is UTC
EventBridge cron expressions use UTC timezone. To schedule in JST (Japan Standard Time), subtract 9 hours.
Example: Run at 7 AM JST → cron(0 22 * * ? *) (10 PM UTC the previous day)
Testing the Setup
I set up a function to send messages to LINE. The setup now sends notifications every 5 minutes:
For testing, set a short interval (like 5 minutes) to verify it works, then change to an appropriate interval for production.
Cost
The EventBridge + Lambda combination is very cost-effective:
| Service | Free Tier | Cost After Free Tier |
|---|---|---|
| EventBridge | Free | Schedule rules are free |
| Lambda | 1M requests/month free | $0.20 per 1M requests |
For personal projects like reminder bots, you can run nearly for free.
Common Pitfalls
1. Timezone Confusion
As mentioned, EventBridge uses UTC. A common mistake is setting “9 AM” and finding it runs at 6 PM instead.
2. Initial Execution Timing
After setting up a cron expression, you need to wait for the next scheduled time. To test immediately, use Lambda’s built-in test feature.
3. Don’t Forget to Delete
Test EventBridge rules left running will keep triggering Lambda. Always delete rules you no longer need.
Summary
This article covered how to schedule Lambda functions with AWS EventBridge.
- EventBridge supports both scheduled execution and event-driven triggers
- Cron expressions use UTC timezone - subtract 9 hours for JST
- Running costs are nearly free for personal projects
- Don’t forget to delete unused rules
Serverless scheduled execution is great for reminder bots and batch processing. Give it a try!