How to grant lambda permission to upload file to s3 bucket in `terraform`?

Question

I have below lambda function configuration in TerraForm:

resource "aws_lambda_function" "test_lambda" {
  # filename         = "crawler/dist/deploy.zip"
  s3_bucket = "${var.s3-bucket}"
  s3_key    = "${aws_s3_bucket_object.file_upload.key}"
  # source_code_hash = "${filebase64sha256("file.zip")}"
  function_name    = "quote-crawler"
  role             = "arn:aws:iam::773592622512:role/LambdaRole"
  handler          = "handler.handler"
  source_code_hash = "${data.archive_file.zipit.output_base64sha256}"
  runtime          = "${var.runtime}"
  timeout          = 180

  environment {
    variables = {
      foo = "bar"
    }
  }
}

when I run the lambda I got the error "errorMessage": "An error occurred (AccessDenied) when calling the PutObject operation: Access Denied", when it tries to upload file to s3 bucket. It seems that the lambda function doesn't have permission to access s3. TerraForm doc is not clear about how to configure them. The permission configuration panel doesn't appear on lambda console either. It seems that lambda that created by TerraForm has limited configuration for me to use. So how can I grant s3 permission to lambda?

Answer 1

To make it easy you can do this in three steps,

1. create a role
2. create policy
3. attached policy to the role
4. attached role to lambda

Create role.

resource "aws_iam_role" "role" {
  name = "${var.env_prefix_name}-alb-logs-to-elk"
  path = "/"

      assume_role_policy = <<EOF
    {

  "Version": "2012-10-17",
  "Statement": [
    {
      "Action": "sts:AssumeRole",
      "Principal": {
        "Service": "lambda.amazonaws.com"
      },
      "Effect": "Allow",
      "Sid": ""
    }
  ]
}
EOF
}

Create a policy that has specified access to s3

 #Created Policy for IAM Role
resource "aws_iam_policy" "policy" {
  name = "${var.env_prefix_name}-test-policy"
  description = "A test policy"


      policy = <<EOF
   {
"Version": "2012-10-17",
"Statement": [
    {
        "Effect": "Allow",
        "Action": [
            "logs:*"
        ],
        "Resource": "arn:aws:logs:*:*:*"
    },
    {
        "Effect": "Allow",
        "Action": [
            "s3:*"
        ],
        "Resource": "arn:aws:s3:::*"
    }
]

} 
    EOF
    }

Attached IAM Role and the new created Policy

resource "aws_iam_role_policy_attachment" "test-attach" {
  role       = "${aws_iam_role.role.name}"
  policy_arn = "${aws_iam_policy.policy.arn}"
}

Now attached the role to Lamba source

resource "aws_lambda_function" "test_lambda" {
  # filename         = "crawler/dist/deploy.zip"
  s3_bucket = "${var.s3-bucket}"
  s3_key    = "${aws_s3_bucket_object.file_upload.key}"
  # source_code_hash = "${filebase64sha256("file.zip")}"
  function_name    = "quote-crawler"
  role             = "${aws_iam_role.role.arn}"
  handler          = "handler.handler"
  source_code_hash = "${data.archive_file.zipit.output_base64sha256}"
  runtime          = "${var.runtime}"
  timeout          = 180

  environment {
    variables = {
      foo = "bar"
    }
  }
}