Gremlin lambda can't DNS resolve the Neptune endpoint

[mmigliari]

Describe the bug The gremlin discovery lambda is unable to resolve the Neptune DNS endpoint, failing with a getaddrinfo EAI_AGAIN <endpoint_address> error.

To Reproduce Launch the stacks as per the documentation and wait for the ECS scheduled task to fire up the lambda. The errors can be seen on the lambda cloudwatch logs with a timeout and the getaddrinfo EAI_AGAIN <endpoint_address> error.

Expected behavior The lambda, which is inside the VPC, should be able to resolve to using the DNS servers defined in the VPC dhcp option set.

Additional context This may be necessary in VPC setups with non-standard DNS settings.

Solution Open outbound UDP port 53 (DNS resolution) access to the lambda for the VPC CIDR range for DHCP options sets with DNS servers hosted in the VPC