Enable Lambda function to an S3 bucket using cloudformation

Question

We are creating an S3 bucket using a CloudFormation template. I would like to associate (Add an event to S3 bucket) a Lambda function whenever a file is added to the S3 bucket.

Answer 1

It is clearly stated in AWS docs that AWS::S3::Bucket is used to create a resource, If we have a bucket that exists already we can not modify it to add NotificationConfiguration. So S3 bucket must not exist for above template to work. Let CloudFormation creates all resources including S3 bucket.

Answer 2

Here's a complete, self-contained CloudFormation template that demonstrates how to trigger a Lambda function whenever a file is added to an S3 bucket:

Description: Upload an object to an S3 bucket, triggering a Lambda event, returning the object key as a Stack Output.
Parameters:
  Key:
    Description: S3 Object key
    Type: String
    Default: test
  Body:
    Description: S3 Object body content
    Type: String
    Default: TEST CONTENT
  BucketName:
    Description: S3 Bucket name
    Type: String
Resources:
  Bucket:
    Type: AWS::S3::Bucket
    DependsOn: BucketPermission
    Properties:
      BucketName: !Ref BucketName
      NotificationConfiguration:
        LambdaConfigurations:
        - Event: 's3:ObjectCreated:*'
          Function: !GetAtt BucketWatcher.Arn
  BucketPermission:
    Type: AWS::Lambda::Permission
    Properties:
      Action: 'lambda:InvokeFunction'
      FunctionName: !Ref BucketWatcher
      Principal: s3.amazonaws.com
      SourceAccount: !Ref "AWS::AccountId"
      SourceArn: !Sub "arn:aws:s3:::${BucketName}"
  BucketWatcher:
    Type: AWS::Lambda::Function
    Properties:
      Description: Sends a Wait Condition signal to Handle when invoked
      Handler: index.handler
      Role: !GetAtt LambdaExecutionRole.Arn
      Code:
        ZipFile: !Sub |
          exports.handler = function(event, context) {
            console.log("Request received:\n", JSON.stringify(event));
            var responseBody = JSON.stringify({
              "Status" : "SUCCESS",
              "UniqueId" : "Key",
              "Data" : event.Records[0].s3.object.key,
              "Reason" : ""
            });
            var https = require("https");
            var url = require("url");
            var parsedUrl = url.parse('${Handle}');
            var options = {
                hostname: parsedUrl.hostname,
                port: 443,
                path: parsedUrl.path,
                method: "PUT",
                headers: {
                    "content-type": "",
                    "content-length": responseBody.length
                }
            };
            var request = https.request(options, function(response) {
                console.log("Status code: " + response.statusCode);
                console.log("Status message: " + response.statusMessage);
                context.done();
            });
            request.on("error", function(error) {
                console.log("send(..) failed executing https.request(..): " + error);
                context.done();
            });
            request.write(responseBody);
            request.end();
          };
      Timeout: 30
      Runtime: nodejs4.3
  Handle:
    Type: AWS::CloudFormation::WaitConditionHandle
  Wait:
    Type: AWS::CloudFormation::WaitCondition
    Properties:
      Handle: !Ref Handle
      Timeout: 300
  S3Object:
    Type: Custom::S3Object
    Properties:
      ServiceToken: !GetAtt S3ObjectFunction.Arn
      Bucket: !Ref Bucket
      Key: !Ref Key
      Body: !Ref Body
  S3ObjectFunction:
    Type: AWS::Lambda::Function
    Properties:
      Description: S3 Object Custom Resource
      Handler: index.handler
      Role: !GetAtt LambdaExecutionRole.Arn
      Code:
        ZipFile: !Sub |
          var response = require('cfn-response');
          var AWS = require('aws-sdk');
          var s3 = new AWS.S3();
          exports.handler = function(event, context) {
            console.log("Request received:\n", JSON.stringify(event));
            var responseData = {};
            if (event.RequestType == 'Create') {
              var params = {
                Bucket: event.ResourceProperties.Bucket,
                Key: event.ResourceProperties.Key,
                Body: event.ResourceProperties.Body
              };
              s3.putObject(params).promise().then(function(data) {
                response.send(event, context, response.SUCCESS, responseData);
              }).catch(function(err) {
                console.log(JSON.stringify(err));
                response.send(event, context, response.FAILED, responseData);
              });
            } else if (event.RequestType == 'Delete') {
              var deleteParams = {
                Bucket: event.ResourceProperties.Bucket,
                Key: event.ResourceProperties.Key
              };
              s3.deleteObject(deleteParams).promise().then(function(data) {
                response.send(event, context, response.SUCCESS, responseData);
              }).catch(function(err) {
                console.log(JSON.stringify(err));
                response.send(event, context, response.FAILED, responseData);
              });
            } else {
              response.send(event, context, response.SUCCESS, responseData);
            }
          };
      Timeout: 30
      Runtime: nodejs4.3
  LambdaExecutionRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
        - Effect: Allow
          Principal: {Service: [lambda.amazonaws.com]}
          Action: ['sts:AssumeRole']
      Path: /
      ManagedPolicyArns:
      - "arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole"
      Policies:
      - PolicyName: S3Policy
        PolicyDocument:
          Version: '2012-10-17'
          Statement:
            - Effect: Allow
              Action:
                - 's3:PutObject'
                - 'S3:DeleteObject'
              Resource: !Sub "arn:aws:s3:::${BucketName}/${Key}"
Outputs:
  Result:
    Value: !GetAtt Wait.Data

Answer 3

i have added below bucket perm along with notificationconfiguration in cloudformation which is used to create S3 bucket..it worked !!

"bucketperm": {
            "Type": "AWS::Lambda::Permission",
            "Properties": {
                "Action": "lambda:invokeFunction",
                "FunctionName": "<arnvalue>",
                "Principal": "s3.amazonaws.com"
            }
}

Answer 4

Yes, it's possible through Cloudformation, and what you need to configure are:

1) AWS::S3::Bucket resource and,

2) NotificationConfiguration configuration (use LambdaConfigurations in this case) for the s3 resource above.

Related documentation that you need:

https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-s3-bucket.html#cfn-s3-bucket-notification

https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-s3-bucket-notificationconfig.html

Answer 5

You need a NotificationConfiguration property in your CloudFormation template. Unfortunately, it seems to require the bucket to already exist. To get around this, you can create an initial stack, then update it with the NotificationConfiguration. For example:

    // template1.json
    {
      "AWSTemplateFormatVersion": "2010-09-09",
      "Parameters": {
        "mylambda": {
          "Type": "String"
        }
      },
      "Resources": {
        "bucketperm": {
          "Type": "AWS::Lambda::Permission",
          "Properties" : {
            "Action": "lambda:InvokeFunction",
            "FunctionName": {"Ref": "mylambda"},
            "Principal": "s3.amazonaws.com",
            "SourceAccount": {"Ref": "AWS::AccountId"},
            "SourceArn": { "Fn::Join": [":", [
                "arn", "aws", "s3", "" , "", {"Ref" : "mybucket"}]]
            }
          }
        },
        "mybucket": {
          "Type": "AWS::S3::Bucket"
        }
      }
    }

    // template2.json -- adds the NotificationConfiguration
    {
      "AWSTemplateFormatVersion": "2010-09-09",
      "Parameters": {
        "mylambda": {
          "Type": "String"
        }
      },
      "Resources": {
        "bucketperm": {
          "Type": "AWS::Lambda::Permission",
          "Properties" : {
            "Action": "lambda:InvokeFunction",
            "FunctionName": {"Ref": "mylambda"},
            "Principal": "s3.amazonaws.com",
            "SourceAccount": {"Ref": "AWS::AccountId"},
            "SourceArn": { "Fn::Join": [":", [
                "arn", "aws", "s3", "" , "", {"Ref" : "mybucket"}]]
            }
          }
        },
        "mybucket": {
          "Type": "AWS::S3::Bucket",
          "Properties": {
            "NotificationConfiguration": {
              "LambdaConfigurations": [
                {
                  "Event" : "s3:ObjectCreated:*",
                  "Function" : {"Ref": "mylambda"}
                }
              ]
            }
          }
        }
      }
    }

You can use the AWS CLI tool to create the stack like this:

    $ aws cloudformation create-stack --stack-name mystack --template-body file://template1.json --parameters ParameterKey=mylambda,ParameterValue=<lambda arn>
    # wait until stack is created
    $ aws cloudformation update-stack --stack-name mystack --template-body file://template2.json --parameters ParameterKey=mylambda,ParameterValue=<lambda arn>