I set custom configuration parameters to the Dynamic Host Configuration Protocol (DHCP) options set for my VPC, but those options aren't passing to the EC2 instances in the VPC. How can I fix this?

Check these resources and configurations to diagnose and troubleshoot the issue:

  • Parameters of the DHCP options set
  • Network configuration and operating system kernel parameters of the EC2 instances
  • Settings of Simple Active Directory (Simple AD) and private hosted zones

Parameters of the DHCP options set

  1. Open the Amazon VPC console.
  2. In the navigation pane, under Virtual Private Cloud, choose DHCP Options Sets.
  3. In the resource list, choose the DHCP options set with your custom configuration parameters.
  4. In the Summary view, verify that the Options follow the guidelines described in Overview of DHCP Options Sets.
    Note: After a DHCP options set is created, it can't be modified. To modify your DHCP options set, create a new DHCP options set with the correct parameters and associate it with your VPC.

Network configuration and operating system kernel parameters of the EC2 instances

  • Search for any customization (PEERDNS, timeouts, etc.) in the network configuration files that were set either manually or using scripts. For more information, see User Data and Shell Scripts.
  • Verify that the configuration files used by the operating system are mutable. If the files are immutable, then the instance won't receive the configuration parameters from the DHCP options set correctly. When using Linux, configuration files are typically made immutable with the chattr command.
  • Check the operating systems of the EC2 instances and search for known bugs. If there's a bug related to the issue, follow the guidelines provided by the operating system. 

Settings of Simple AD and private hosted zones

  • You can resolve DNS requests to your Amazon Route 53 private hosted zone by pointing your on-premises computers to Simple AD, which forwards DNS requests to your VPC's Amazon-provided DNS servers. For more information, see Using DNS with Simple AD and Microsoft AD.
  • If you're using a custom hostname, confirm that the DNS server in the DHCP options set has proper zone definitions and DNS records for your custom domain. Additionally, be sure that you have manually configured the custom hostname on the EC2 instance. For more information, see Changing the Hostname of Your Linux Instance and Working with Private Hosted Zones.

Note: To configure your VPC for Simple AD, you can customize your DHCP options set to use your directory's DNS servers. Or, you can use the default DHCP options set, but you must then manually join the instances to the Simple AD directory.

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Published: 2017-12-14