AWS Directory Service unable to resolve EFS dns name

Question

Hello,  
  
I am using AWS Directory Service and therefore my VPC has the required custom DHCP options. This seems to be causing my EFS dns name to not resolve:  
  
$ sudo mount -t efs fs-981781a1:/ efs  
Failed to resolve "fs-981781a1.efs.ap-southeast-2.amazonaws.com" - check that your file system ID is correct.  
  
$ sudo mount -t nfs4 -o nfsvers=4.1,rsize=1048576,wsize=1048576,hard,timeo=600,retrans=2,noresvport fs-981781a1.efs.ap-southeast-2.amazonaws.com:/ efs  
mount.nfs4: Failed to resolve server fs-981781a1.efs.ap-southeast-2.amazonaws.com: Name or service not known  
  
However, specifying the EFS target ip address does work:  
sudo mount -t nfs4 -o nfsvers=4.1,rsize=1048576,wsize=1048576,hard,timeo=600,retrans=2,noresvport 10.0.14.62:/ efs  
  
Any help would be appreciated.  
  
Thanks!

Accepted Answer

There are two areas you can check:  
  
1. Verify that the DNS service provided by AWS Directory Service is configured to forward unknown quries to your .2 DNS server.  Given the EFS IP you provided I would guess that DNS server is at 10.0.0.2.  Here is a screenshot showing where to configure the forwarder.  
http://www.mcmcse.com/microsoft/guides/70-410/images/dns_forwarding1.jpg  
  
2. EFS creates mount targets at the AZ level.  So if you have instances in three AZs and only created mount targets in two AZs, then the instances in the third AZ without a mount target will not be able to resolve the name.  
The common problem we hear about in Directory Service is that the EFS mount target is only in AZ A and the Directory Service domain controllers are in AZ B and C.  The EC2 instances send all of their DNS queries to the domain controllers and they then forward the lookup to the .2 DNS server in their AZ.  But since there isn't a mount target in the domain contorller's AZ the .2 DNS server gives an NX (non-existent) response and the domain controller forwards that response to the EC2 instance.  The easy fix in this scenario is to create EFS mount targets in all of the AZs where you have provisioned Directory Service domain controllers.

Answer

Sorry, but we have not provided a way to alter the forwarder setting through the console or a public API.  Configuring it through a domain joined EC2 instance is the only option available today.

Answer

Hello,  
  
Thank you for your reply.  
  
My EFS, managed Microsoft AD Directory Service and EC2 are all using the same subnet/availability zone. However, I had no idea I needed to setup a forwarder for unknown queries. I provisioned the managed Microsoft AD Directory Service using a cloudformation template based upon the following:  
https://github.com/aws-quickstart/quickstart-microsoft-activedirectory/blob/master/templates/ad-3.template  
  
Preferrable I'd like to add the additional setup of the forwarder to it.  
  
If I was to do it manually do I really need to install DNS Manager tools on a windows EC2 instance? Or can it be done in the Directory Service console?  
  
Any help would be appreciated.  
  
Thanks

AWS Directory Service unable to resolve EFS dns name

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