Lambda can listen to various types of CloudWatch events. One of the simplest types of events is CloudWatch Scheduled Event (similar to Cron job).

Just create a serverless.yml with

service: cloudwatch-event-handler

provider:
  name: aws
  runtime: nodejs8.10
  region: eu-west-1
  profile: default
  memorySize: 256 # optional, in MB, default is 1024
  stage: dev

functions:
  signInCloudWatchEvent:
    handler: handler.signInCloudWatchEvent
    events:
      - cloudwatchEvent:
        event:
          source:
            - aws.events

and handler.js with

module.exports.signInCloudWatchEvent = (event, context, callback) => {
  console.log('EVENT', JSON.stringify(event)),
  callback(null);
}

 

After deploying this stack, you can attach this lambda to CloudWatch Event. For example, you can create a new Rule with Schedule of a fixed rate 1 minute in AWS Console. In Targets section set cloudwatch-event-handler-dev-signInCloudWatchEvent as listening lambda function. After that you should start receiving events on this lambda:

{
    "version": "0",
    "id": "397c14ce-20b1-cc14-dbca-9deca327fca9",
    "detail-type": "Scheduled Event",
    "source": "aws.events",
    "account": "189075651281",
    "time": "2018-06-05T10:48:38Z",
    "region": "eu-west-1",
    "resources": [
        "arn:aws:events:eu-west-1:189075651281:rule/test_rule"
    ],
    "detail": {}
}

Now, you can listen to a Scheduler Event from using cron-like CloudWatch functionality. Every time the event is fired, your lambda will be invoked.