CODEWITHSUNDEEP
amazon-web-servicesaws-lambdaaws-cloudformationamazon-cloudwatch
Agniv
Agniv

Reputation: 137

AWS CloudWatch Event Rule - Invoke Lambda with Parameter

I am using an AWS CloudWatch Event Rule to invoke a Python Lambda function based on Cron Schedule, which is working fine. Now can I pass a parameter into this Lambda function from CloudWatch Event Rule using AWS CloudFormation? Here is my cfn template:

Step 1: parameter.Schedule=cron(0 21 ? * * *)

Step 2: "Schedule": {
            "Description": "Schedule for the Lambda function (cron or rate)",
            "Type": "String"
         },
          
          
Step 3:  "funcInvokeRule": {
            "Type": "AWS::Events::Rule",
            "Properties": {
                "ScheduleExpression": {"Ref": "Schedule"},
                "Targets": [{
                    "Id": "funcScheduler",
                    "Arn": {"Fn::GetAtt": ["Function","Arn"]}
                }]
             }
          },

Upvotes: 4

Views: 7461

Answers (3)

T. Pubz
T. Pubz

Reputation: 75

As @Marcin pointed out, the Input parameter of the Targets property is what you want. Keep in mind the format is JSON text so ensure you escape special chars. Here is an example using your CloudFormation resource:

"funcInvokeRule": {
    "Type": "AWS::Events::Rule",
    "Properties": {
        "ScheduleExpression": {"Ref": "Schedule"},
        "Targets": [{
            "Id": "funcScheduler",
            "Arn": {"Fn::GetAtt": ["Function","Arn"]},
            "Input": "{\"foo\":\"val\",\"bar\":{\"baz\":\"nested_val\"}}"
        }]
    }
}

Upvotes: 1

pkarfs
pkarfs

Reputation: 1039

Following the AWS docs, your cloudformation resource could be as simple as:

Resources:  
  EventRule:
    Type: AWS::Events::Rule
    Properties:
      Name: {EVENTNAME}
      Description: "ScheduledRule"
      ScheduleExpression: cron(0 21 ? * * *)
      State: "ENABLED"
      RoleArn: {ROLE}

Replacing Name and RoleArn with your own values.

Note: Name is not a required parameter but does help identify your resources. However, as per the documentation, if you replace the resource in your cloudformation template you specify a new name.

If you were then also going to use cloudformation for your lambda using severless, personally I would then attached the rule to the lambda via permissions, that way you can attach up to 5 triggers on the rule without modifying the rule targets every time. e.g.

  Lambda:
    Type: AWS::Serverless::Function
    Properties:
      FunctionName:{LAMBDANAME}
      Description: {Description}
      Role: {Role}
      Handler: {FileName}.lambda_handler
      Runtime: {x}
      CodeUri: {ObjectPath}
      MemorySize: {x}
      Timeout: {x}
  Lambdatrigger:
    Type: AWS::Lambda::Permission
    Properties:
      FunctionName: !Ref Lambda
      Action: lambda:InvokeFunction
      Principal: events.amazonaws.com
      SourceArn: !Ref EventRule

Upvotes: 0

Marcin
Marcin

Reputation: 238051

The Target property type of AWS::Events::Rule has Input parameter:

Valid JSON text passed to the target. If you use this property, nothing from the event text itself is passed to the target.

There is also InputTransformer which you can use to transform existing input, by for example, adding extra values to it.

Settings to enable you to provide custom input to a target based on certain event data. You can extract one or more key-value pairs from the event and then use that data to send customized input to the target.

Upvotes: 2

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