Error with connecting lambda function to S3 bucket. \"statusCode\": 500, \"body\": \"An error occurred (AccessDenied) when calling the ListBuckets operation: Access Denied\"

Question

I am aware that this means I "don't have permission to list buckets" in my lambda function but I have double checked all my policies and permissions and it should work. Im just confused as to why. I know my lambda function code is written very inefficiently but I am just trying to figure out why I can't access files in my bucket. I am very new to AWS and just trying to get this to work.

Lambda Function:

```
import json
import pandas
import datetime
import boto3

#import cartopy

def lambda_handler(event, context):
    x = event['queryStringParameters']['x']
    y = event['queryStringParameters']['y']

print(f" x:{x} , y:{y}")

res_body = {}
    res_body['x'] = str(x)
    res_body['y'] = str(y)
    res_body['ans'] = add(x,y)

http_res = {}
    http_res['statusCode'] = 200
    http_res['headers'] = {
        "Content-Type": "application/json",
        "Access-Control-Allow-Headers": "Content-Type",
        "Access-Control-Allow-Origin": "*",
        "Access-Control-Allow-Methods": "GET"
    }
    http_res['body'] = json.dumps(res_body)

return http_res
def add(x,y):
    bucket_name = "aerocastwx.com"
    file_name = "/model_csv/delte.csv"
    print("Getting S3")
    # Create an S3 client

try:
        aws_access_key_id = 'xx'
        aws_secret_access_key = 'xx'
        
        # Create an S3 client
        s3 = boto3.client(
            's3',
            aws_access_key_id=aws_access_key_id,
            aws_secret_access_key=aws_secret_access_key
        )
        #response = s3.get_object(Bucket=bucket_name, Key=file_name)
        # Example: List S3 buckets
        response = s3.list_buckets()
        
        # Print the bucket names
        #print("S3 Buckets:")
        #for bucket in response['Buckets']:
            #print(f"- {bucket['Name']}")

except Exception as e:
        return {
            'statusCode': 500,
            'body': str(e)
        }
    return x+y+y

```
Here are images of the permissions for lambda function, s3 bucket, IAM user:
![Enter image description here](/media/postImages/original/IMs4XQYM9PRIyQiSzDRsaeJQ)
![Enter image description here](/media/postImages/original/IMZokFXZehSviNb0EouVS9Og)
![Enter image description here](/media/postImages/original/IMsScnpbe9SVWPoYrJlZ_YcA)

Answer

Hello.

Looking at the code, it seems to be using an access key when listing S3.  
You can set an IAM role for Lambda, so there is no need to set an access key.  
Another possible cause of the error is that the IAM user who issued the access key does not have permissions.  
Please try deleting the access key from Lambda and setting access rights to S3 in the IAM role.  
```
        aws_access_key_id = 'xx'
        aws_secret_access_key = 'xx'
        
        # Create an S3 client
        s3 = boto3.client(
            's3',
            aws_access_key_id=aws_access_key_id,
            aws_secret_access_key=aws_secret_access_key
        )
        #response = s3.get_object(Bucket=bucket_name, Key=file_name)
        # Example: List S3 buckets
        response = s3.list_buckets()
```

Answer

Your code is performing a [`ListBuckets`](https://docs.aws.amazon.com/AmazonS3/latest/API/API_ListBuckets.html) call, and your IAM permissions are allowing `s3:ListBucket`. You need `s3:ListAllMyBuckets` in order to call ListBuckets.

If you update your IAM policy to:

```
{
	"Version": "2012-10-17",
	"Statement": [
		{
			"Sid": "SamplePolicy",
			"Effect": "Allow",
			"Action": "s3:ListAllMyBuckets",
			"Resource": "*"
		}
	]
}
```

Then your code will work as intended.

Best practice of course is what is described by Riko, and to use a role in Lambda (which would need the same permissions I talk about here), and not to use static credentials the way you are.

Error with connecting lambda function to S3 bucket. \"statusCode\": 500, \"body\": \"An error occurred (AccessDenied) when calling the ListBuckets operation: Access Denied\"

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