This template demonstrates how to develop and deploy a simple cron-like service running on AWS Lambda using the traditional Serverless Framework.
Schedule event type
This examples defines two functions, rateHandler and cronHandler, both of which are triggered by an event of schedule type, which is used for configuring functions to be executed at specific time or in specific intervals. For detailed information about schedule event, please refer to corresponding section of Serverless docs.
When defining schedule events, we need to use rate or cron expression syntax.
Rate expressions syntax
value - A positive number
unit - The unit of time. ( minute | minutes | hour | hours | day | days )
In below example, we use rate syntax to define schedule event that will trigger our rateHandler function every minute
functions: rateHandler: handler: handler.run events: - schedule: rate(1 minute)
Detailed information about rate expressions is available in official AWS docs.
Cron expressions syntax
cron(Minutes Hours Day-of-month Month Day-of-week Year)
All fields are required and time zone is UTC only.
| Field | Values | Wildcards |
|---|---|---|
| Minutes | 0-59 | , - * / |
| Hours | 0-23 | , - * / |
| Day-of-month | 1-31 | , - * ? / L W |
| Month | 1-12 or JAN-DEC | , - * / |
| Day-of-week | 1-7 or SUN-SAT | , - * ? / L # |
| Year | 192199 | , - * / |
In below example, we use cron syntax to define schedule event that will trigger our cronHandler function every second minute every Monday through Friday
functions: cronHandler: handler: handler.run events: - schedule: cron(0/2 * ? * MON-FRI *)
Detailed information about cron expressions in available in official AWS docs.
Usage
Deployment
This example is made to work with the Serverless Framework dashboard, which includes advanced features such as CI/CD, monitoring, metrics, etc.
In order to deploy with dashboard, you need to first login with:
and then perform deployment with:
After running deploy, you should see output similar to:
Serverless: Packaging service... Serverless: Excluding development dependencies... Serverless: Uploading CloudFormation file to S3... Serverless: Uploading artifacts... Serverless: Uploading service aws-python-scheduled-cron.zip file to S3 (84.82 KB)... Serverless: Validating template... Serverless: Updating Stack... Serverless: Checking Stack update progress... ........................ Serverless: Stack update finished... Service Information service: aws-python-scheduled-cron stage: dev region: us-east-1 stack: aws-python-scheduled-cron-dev resources: 16 api keys: None endpoints: None functions: rateHandler: aws-python-scheduled-cron-dev-rateHandler cronHandler: aws-python-scheduled-cron-dev-cronHandler layers: None Serverless: Publishing service to the Serverless Dashboard... Serverless: Successfully published your service to the Serverless Dashboard: https://app.serverless.com/xxxx/apps/xxxx/aws-python-scheduled-cron/dev/us-east-1
There is no additional step required. Your defined schedules becomes active right away after deployment.
Local invocation
In order to test out your functions locally, you can invoke them with the following command:
serverless invoke local --function rateHandler
After invocation, you should see output similar to:
INFO:handler:Your cron function aws-python-scheduled-cron-dev-rateHandler ran at 15:02:43.203145
Bundling dependencies
In case you would like to include 3rd party dependencies, you will need to use a plugin called serverless-python-requirements. You can set it up by running the following command:
serverless plugin install -n serverless-python-requirements
Running the above will automatically add serverless-python-requirements to plugins section in your serverless.yml file and add it as a devDependency to package.json file. The package.json file will be automatically created if it doesn't exist beforehand. Now you will be able to add your dependencies to requirements.txt file (Pipfile and pyproject.toml is also supported but requires additional configuration) and they will be automatically injected to Lambda package during build process. For more details about the plugin's configuration, please refer to official documentation.