This article focuses on the forwarding configuration for custom DNS used by Volcano Engine E-MapReduce (EMR) clusters. This document only supports scenarios where a self-managed DNS can access the Volcano Name Server (100.96.0.2, 100.96.0.3). Otherwise, refer to this document for modifications.
EMR uses PrivateZone to manage node domain names within the cluster. For specific rules, see Domain name rules. When creating a cluster in a VPC where a custom DNS server is specified (the DNS field on the VPC overview page), you must configure the appropriate forwarding rules on the self-managed DNS server. Otherwise, cluster creation will be affected. In addition, modifying the DNS properties of the VPC after the cluster is created will also affect cluster scaling and communication between components within the cluster.
Therefore, when using a custom DNS server, you need to configure the corresponding forwarding rules to forward the resolution of specific domain names to Volcano DNS. The following uses CoreDNS as an example for the relevant configuration.

1. DNS forwarding configuration #

First, determine the corresponding domain name based on the version of the cluster you want to create (see Domain name rules).

• If you are creating EMR 3.4.0/2.3.0 or earlier versions and the VPC ID is vpc-123456, then the domain name that needs to be forwarded is emr-123456.internal.
• For EMR 3.5.0/2.4.0 and later versions, the domain name that needs to be forwarded is emr-volces.com.

The following provides a basic configuration example for emr-volces.com. Other configurations can be added or adjusted as needed.
To prevent negative caching from affecting cluster creation and scaling, negative caching is disabled here. If you want to enable negative caching, it is recommended that the cache time does not exceed 10 seconds.

emr-volces.com {
    forward . 100.96.0.2 100.96.0.3
    cache {
        disable denial
    }
}

Related Volcano services will access ivolces.com on the private network. It is also recommended to configure this accordingly.

ivolces.com {
    forward . 100.96.0.2 100.96.0.3
}

2. Additional configuration for Kerberos clusters #

In addition, if the cluster you create has Kerberos enabled, you need to additionally configure reverse domain name resolution. Other configurations can be added or adjusted as needed.
For the same reason, negative caching is also disabled here. In addition, because frequent scaling operations may use the same IP, the positive cache time is set to 5 seconds. If you want to adjust it, it is recommended not to exceed 10 seconds.
Determining the reverse domain name

1. If there is no conflict with your existing domain names, you can use in-addr.arpa directly.
2. If you require a more granular domain name, check the CIDR of your VPC. EMR will attempt to use an IP block with a network prefix divisible by 8 to construct the reverse DNS domain whenever possible.
   1. For example, if your VPC's CIDR is 192.168.0.0/16, the constructed reverse DNS domain is 168.192.in-addr.arpa.
   2. For example, if your VPC's CIDR is 192.168.0.0/17, the constructed reverse DNS domain is 168.192.in-addr.arpa.
   3. For example, if your VPC's CIDR is 192.168.1.0/25, the constructed reverse DNS domain is 1.168.192.in-addr.arpa.

The following uses 1.168.192.in-addr.arpa as an example.

1.168.192.in-addr.arpa {
    forward . 100.96.0.2 100.96.0.3
    cache {
        success 5000 5
        disable denial
    }
}