AWS Neptune OpenSearch Replication

The errors you're encountering with Neptune to OpenSearch replication appear to be related to network connectivity issues. These connection problems are likely due to VPC configuration issues between your Lambda function and the required AWS services.

Based on the error messages, there are two main issues:

1. Connection reset errors when the Lambda function is trying to communicate with Neptune or OpenSearch
2. Connection timeout when trying to reach CloudWatch monitoring endpoints

Here are some potential solutions:

1. Verify VPC configuration:

• Ensure that the OpenSearch cluster and Lambda function are located in the same VPC as your Neptune DB cluster
• Confirm that the OpenSearch cluster is configured in VPC mode (not Internet mode)
• Check that security groups allow proper communication between Lambda, Neptune, and OpenSearch

2. Check security group rules:

• Make sure the security group for your Lambda function allows outbound traffic to Neptune (port 8182) and OpenSearch (port 443)
• Verify that the security groups for Neptune and OpenSearch allow inbound traffic from the Lambda function's security group

3. Network connectivity:

• Ensure your VPC has proper NAT Gateway configuration to allow the Lambda function to access AWS services like CloudWatch
• If your Lambda is in a private subnet, it needs a route to access AWS services via a NAT Gateway or VPC endpoints

4. VPC Endpoints:

• Consider adding VPC endpoints for services like CloudWatch, Neptune, and OpenSearch to improve connectivity reliability
• This can help resolve the timeout issues when connecting to monitoring.ap-south-1.amazonaws.com

Since the issue is intermittent, it suggests potential resource constraints or temporary network issues. You might want to increase the Lambda function's timeout and memory allocation to handle these occasional connectivity problems.
Sources
Amazon Neptune-to-OpenSearch replication - Amazon Neptune
Lambda (inside VPC) using Neptune API results in error: EndpointConnectionError: Could not connect to the endpoint URL | AWS re:Post
Cannot curl OpenSearch Service Endpoint from VPN Client Endpoint | AWS re:Post

Looking at the error messages it looks like the Stream poller is failing with a timeout error while publishing metrics to CloudWatch. This can happen if:

• The VPC endpoint for monitoring is removed, or has had its configuration changed.
• The VPC Security Group rules are not allowing outbound traffic to CloudWatch endpoints
• Something like network ACLs are blocking the connection
• Something else is causing the writes to timeout

Please also note that the Java version of the poller was deprecated about two years ago, and the Python version is the recommended/supported one to use.