AWS Lambda scheduled event source via cloudformation

Use Aws::Event::Rule with a ScheduleExpression and a AWS::Lambda::Permission

// rule to periodically call the lambda
"TagWatcherRule": {
  "Type": "AWS::Events::Rule",
  "Properties": {
    "ScheduleExpression": "rate(10 minutes)",
    "Targets": [
      {
        "Id": "TagWatcherScheduler",
        "Arn": {
          "Fn::GetAtt": [
            "TagWatcherFunction",
            "Arn"
          ]
        }
      }
    ]
  }
},
// role may call the lambda
"InvokeLambdaPermission": {
  "Type": "AWS::Lambda::Permission",
  "Properties": {
    "FunctionName": {
      "Fn::GetAtt": [
        "TagWatcherFunction",
        "Arn"
      ]
    },
    "Action": "lambda:InvokeFunction",
    "Principal": "events.amazonaws.com",
    "SourceArn": {
      "Fn::GetAtt": [
        "TagWatcherRule",
        "Arn"
      ]
    }
  }
}

I solved same problem.

"RoleForLambdaStopEC2Instances" : {
  "Type": "AWS::IAM::Role",
  "Properties": {
    "AssumeRolePolicyDocument": {
      "Version": "2012-10-17",
      "Statement": [
        {
          "Sid": "",
          "Effect": "Allow",
          "Principal": {
            "Service": "lambda.amazonaws.com"
          },
          "Action": "sts:AssumeRole"
        }
      ]
    },
    "Policies": [
      {
        "PolicyName": "LambdaStopEC2InstancesPolicy",
        "PolicyDocument": {
          "Version": "2012-10-17",
          "Statement": [
            {
              "Effect": "Allow",
              "Action": [
                "logs:CreateLogGroup",
                "logs:CreateLogStream",
                "logs:PutLogEvents",
                "ec2:StopInstances"
              ],
              "Resource": [
                "arn:aws:logs:*:*:*",
                "arn:aws:ec2:*"
              ]
            }
          ]
        }
      }
    ],
    "Path": "/"
  }
},
"LambdaStopEC2Instances": {
  "Type": "AWS::Lambda::Function",
  "Properties": {
    "Code": {
      "S3Bucket": "XXXXXXXXXXXXXXXXX",
      "S3Key": "XXXXXXXXXXXXXXXXXX"
    },
    "Handler": "stopEC2Instances.handler",
    "Role": { "Fn::GetAtt" : ["RoleForLambdaStopEC2Instances", "Arn"] },
    "Runtime": "nodejs4.3",
    "Timeout": "5"
  }
},
"StopEC2InstancesRule": {
  "Type" : "AWS::Events::Rule",
  "Properties" : {
    "Name" : "StopEC2Instances",
    "ScheduleExpression" : "cron(0 13 ? * MON-FRI *)",
    "State": "ENABLED",
    "Targets": [{
      "Arn": { "Fn::GetAtt": ["LambdaStopEC2Instances", "Arn"] },
      "Id": "stopEC2Instances"
    }]
  }
},
"LambdaInvokePermission": {
  "Type": "AWS::Lambda::Permission",
  "Properties": {
    "FunctionName" : { "Fn::GetAtt" : ["LambdaStopEC2Instances", "Arn"] },
    "Action": "lambda:InvokeFunction",
    "Principal": "events.amazonaws.com",
    "SourceAccount": { "Ref" : "AWS::AccountId" },
    "SourceArn": { "Fn::GetAtt": ["StopEC2InstancesRule","Arn"] }
  }
}