Accessing AWS Elasticsearch from Lambda Function

Question

I am trying to access my AWS Elasticsearch from a Lambda function.

Using the Serverless Framework and an IP-based access policy, I was already able to achieve this locally.

For the deployed lambda function I tried using the ARN of the Lambda Function Role and the ARN of the Lambda function (the one on the top right when viewing the function in the console) in my access policy.

Sadly I still get the following error: User: anonymous is not authorized to perform: es:ESHttpPost

This is my AWS Access Policy:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {
        "AWS": "arn-of-lambda-function-role"
      },
      "Action": "es:*",
      "Resource": "my-resource-arn"
    },
    {
      "Effect": "Allow",
      "Principal": {
        "AWS": "*"
      },
      "Action": "es:*",
      "Resource": "my-resource-arn",
      "Condition": {
        "IpAddress": {
          "aws:SourceIp": "my-ip"
        }
      }
    }
  ]
}

Answer 1

Are you signing your requests to the ES instance? According to the https://docs.aws.amazon.com/elasticsearch-service/latest/developerguide/es-ac.html#es-managedomains-signing-service-requests

To make calls to the Elasticsearch APIs, you must sign your own requests.