Access Denied Error 500 Deleting Object in S3 Bucket from Lambda function using NodeJS and Postman

Question

I need to delete an object in S3 from a Lambda function. I have tried everything, and this is driving me crazy, please help!

I have a lambda function associated with an API GATEWAY from AWS. When I make the request in Postman, I receive an Access Denied message with a 500 internal server error code. The CloudWatch logs don't show additional info.

Postman response

When I use the AWS CLI, i can delete the object succesfully using this command:

aws s3api delete-object --bucket <<My-Bucket>> --key <<My-Key>>

Additionally, I can upload files to S3 with another request in Postman, without any problem.

But when I use the code uploaded to Lambda, it doesn't work. I am using AWS SDK v3, but I have already tried with older versions. The relevant code is the following:

const {S3Client, DeleteObjectCommand} = require("@aws-sdk/client-s3");
const client = new S3Client({region: process.env.AWS_REGION});
const command = new DeleteObjectCommand({
    Bucket: process.env.BUCKET_NAME, Key: `posts/${familyId}/${magazineId}/${postId}`
            });
await client.send(command);

My IAM user has S3 Full Access. IAM user permissions

The bucket owner is this IAM user. The policy of my S3 bucket is the following:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Principal": {
                "AWS": "arn:aws:iam::<<My-account-id>>:user/<<My-username>>"
            },
            "Action": [
                "s3:ListBucket"
            ],
            "Resource": "arn:aws:s3:::<<My-bucket>>"
        },
        {
            "Effect": "Allow",
            "Principal": {
                "AWS": "arn:aws:iam::<<My-account-id>>:user/<<My-username>>"
            },
            "Action": [
                "s3:PutObject",
                "s3:PutObjectAcl",
                "s3:GetObject",
                "s3:GetObjectAcl",
                "s3:DeleteObject"
            ],
            "Resource": "arn:aws:s3:::<<My-bucket>>/*"
        }
    ]
}

I tried unblocking public access, but the problem remains. The command:

aws configure list

Shows me the access key, secret key and region that I expect. Any idea would be highly appreciated, thank you!!

Answer 1

Answering myself as I found the solution:

I am using AWS SAM to deploy the lambda functions (infrastructure as code). I was missing the permissions needed in template.yml. Added this policy to the lambda function in template.yml and it worked.

MyFunction:
    Type: AWS::Serverless::Function
    Properties:
          Policies:
            - S3CrudPolicy:
                BucketName: !Ref BucketName

Check these docs to troubleshoot additional access denied errors: https://aws.amazon.com/premiumsupport/knowledge-center/s3-troubleshoot-403/

Hope it helps!