create folder inside S3 bucket using Cloudformation

Question

I\'m able to create an S3 bucket using cloudformation but would like to create a folder inside an S3 bucket..like

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Answer 1

AWS doesn't provide an official CloudFormation resource to create objects within an S3 bucket. However, you can create a Lambda-backed Custom Resource to perform this function using the AWS SDK, and in fact the gilt/cloudformation-helpers GitHub repository provides an off-the-shelf custom resource that does just this.

As with any Custom Resource setup is a bit verbose, since you need to first deploy the Lambda function and IAM permissions, then reference it as a custom resource in your stack template.

First, add the Lambda::Function and associated IAM::Role resources to your stack template:

"S3PutObjectFunctionRole": {
  "Type": "AWS::IAM::Role",
  "Properties": {
    "AssumeRolePolicyDocument": {
      "Version" : "2012-10-17",
      "Statement": [
        {
          "Effect": "Allow",
          "Principal": {
            "Service": [ "lambda.amazonaws.com" ]
          },
          "Action": [ "sts:AssumeRole" ]
        }
      ]
    },
    "ManagedPolicyArns": [
      { "Ref": "RoleBasePolicy" }
    ],
    "Policies": [
      {
        "PolicyName": "S3Writer",
        "PolicyDocument": {
          "Version" : "2012-10-17",
          "Statement": [
            {
              "Effect": "Allow",
              "Action": [
                "s3:DeleteObject",
                "s3:ListBucket",
                "s3:PutObject"
              ],
              "Resource": "*"
            }
          ]
        }
      }
    ]
  }
},
"S3PutObjectFunction": {
  "Type": "AWS::Lambda::Function",
  "Properties": {
    "Code": {
      "S3Bucket": "com.gilt.public.backoffice",
      "S3Key": "lambda_functions/cloudformation-helpers.zip"
    },
    "Description": "Used to put objects into S3.",
    "Handler": "aws/s3.putObject",
    "Role": {"Fn::GetAtt" : [ "S3PutObjectFunctionRole", "Arn" ] },
    "Runtime": "nodejs",
    "Timeout": 30
  },
  "DependsOn": [
    "S3PutObjectFunctionRole"
  ]
},

Then you can use the Lambda function as a Custom Resource to create your S3 object:

"MyFolder": {
  "Type": "Custom::S3PutObject",
  "Properties": {
    "ServiceToken": { "Fn::GetAtt" : ["S3PutObjectFunction", "Arn"] },
    "Bucket": "mybucket",
    "Key": "myfolder/"
  }
},

You can also use the same Custom Resource to write a string-based S3 object by adding a Body parameter in addition to Bucket and Key (see the docs).