Serverless Framework Python Scheduled Cron on AWS

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

rate(value unit)

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:

serverless login

and then perform deployment with:

serverless deploy

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.