1. Copy this workflow and select the event source tied to your RSS feed. This will run the workflow every time a new item appears in the feed.
2. Create an IAM user and attach an IAM policy of the following format:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "VisualEditor0",
            "Effect": "Allow",
            "Action": "lambda:InvokeFunction",
            "Resource": "[your-lambda-arn]"
        }
    ]
}

This assumes you have an existing Lambda you'd like to invoke. If not, go ahead an create one now.

1. Click the Connect Account button in invoke_lambda step, saving your AWS access and secret keys from Step 2 above.
2. Add the name of your Lambda function as the value of the Lambda Function Name parameter.
3. Deploy the workflow. Every time a new item shows up in your RSS feed, this workflow will trigger your Lambda.