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    Implementing Custom Domain Name Resolution in TKE

    Last updated: 2023-03-27 11:08:16
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      Overview

      When using a TKE or TKE Serverless cluster, you may need to resolve the custom internal domain names in the following scenarios:
      You build an external centralized storage service, and want to send the monitoring or log collection data in the cluster to the external storage service through a fixed internal domain name.
      During the containerization of traditional services, the code of some services is configured to call other internal services through a fixed domain name, and the configuration cannot be modified, that is, the Service name of Kubernetes cannot be used for calling.

      Solutions

      This document describes the following three solutions for using custom domain name resolution in a cluster:
      Solution
      Benefits
      This solution is simple and intuitive. You can add arbitrary resolution records.
      You do not need to know the IP address of a resolution record in advance, but the IP address mapped by the resolution record must be deployed in the cluster.
      You can manage a large number of resolution records. As all records are managed in the external DNS, you do not need to modify the CoreDNS configuration when adding or deleting records.
      Note
      In the first two solutions, you need to modify the CoreDNS configuration file each time you add a resolution record. The modification takes effect without restart. Select a solution based on your actual needs.

      Examples

      Solution 1: Using the CoreDNS hosts plugin to configure arbitrary domain name resolution

      1. Run the following command to modify the configmap of CoreDNS, as shown below:
      kubectl edit configmap coredns -n kube-system
      2. Modify the hosts configuration by adding the relevant domain names, as shown below:
      hosts {
           192.168.1.6     harbor.example.com
           192.168.1.8     es.example.com
           fallthrough
      }
      Description
      Map harbor.example.com to 192.168.1.6 and es.example.com to 192.168.1.8.
      The complete configurations are as follows:
      apiVersion: v1
      data:
            Corefile: |2-
              .:53 {
                  errors
                  health
                  kubernetes cluster.local. in-addr.arpa ip6.arpa {
                      pods insecure
                      upstream
                      fallthrough in-addr.arpa ip6.arpa
                  }
                  hosts {
                      192.168.1.6     harbor.example.com
                      192.168.1.8     es.example.com
                      fallthrough
                  }
                  prometheus :9153
                  forward . /etc/resolv.conf
                  cache 30
                  reload
                  loadbalance
              }
      kind: ConfigMap
      metadata:
            labels:
              addonmanager.kubernetes.io/mode: EnsureExists
            name: coredns
            namespace: kube-system

      Solution 2: Using the CoreDNS rewrite plugin to map a domain name to a service in the cluster

      If you need to deploy a service with a custom domain name in a cluster, you can use the Rewrite plugin of CoreDNS to resolve the specified domain name to the ClusterIP of a Service.
      1. Run the following command to modify the configmap of CoreDNS, as shown below:
      kubectl edit configmap coredns -n kube-system
      2. Run the following command to add the rewrite configuration, as shown below:
      rewrite name es.example.com es.logging.svc.cluster.local
      Description
      Map the es.example.com domain name to the es service deployed in the logging namespace. Separate multiple domain names with carriage returns.
      The complete configurations are as follows:
      apiVersion: v1
      data:
            Corefile: |2-
              .:53 {
                  errors
                  health
                  kubernetes cluster.local. in-addr.arpa ip6.arpa {
                      pods insecure
                      upstream
                      fallthrough in-addr.arpa ip6.arpa
                  }
                  rewrite name es.example.com es.logging.svc.cluster.local
                  prometheus :9153
                  forward . /etc/resolv.conf
                  cache 30
                  reload
                  loadbalance
              }
      kind: ConfigMap
      metadata:
            labels:
              addonmanager.kubernetes.io/mode: EnsureExists
            name: coredns
            namespace: kube-system

      Solution 3: Using the CoreDNS forward plugin to set the external DNS as the upstream DNS

      1. Check the forward configuration. The default configuration of forward is as follows, which means that the domain name that is not in the cluster is resolved by the nameserver configured in the /etc/resolv.conf file of the node where CoreDNS is located.
      forward . /etc/resolv.conf
      2. Configure forward by replacing /etc/resolv.conf explicitly with the IP address of the external DNS server, as shown below:
      forward . 10.10.10.10
      The complete configurations are as follows:
      apiVersion: v1
      data:
         Corefile: |2-
           .:53 {
               errors
               health
               kubernetes cluster.local. in-addr.arpa ip6.arpa {
                   pods insecure
                   upstream
                   fallthrough in-addr.arpa ip6.arpa
               }
               prometheus :9153
               forward . 10.10.10.10
               cache 30
               reload
               loadbalance
           }
      kind: ConfigMap
      metadata:
         labels:
           addonmanager.kubernetes.io/mode: EnsureExists
         name: coredns
         namespace: kube-system
      3. Configure the resolution records of the custom domain names to the external DNS. We recommend that you set the nameserver in /etc/resolv.conf on the node as the upstream of the external DNS. If it is not set as the upstream of the external DNS, some services may not work properly because the services rely on internal DNS resolution of Tencent Cloud. This document takes BIND 9 as an example to modify the configuration file and write the upstream DNS address into forwarders, as shown below:
      Note
      If the external DNS Server and the request source are not in the same Region, some Tencent domain names that do not support cross-region access may become invalid.
      options {
           forwarders {
                   183.60.83.19;
                   183.60.82.98;
           };
           ...

      Learn More

      CoreDNS hosts plugin
      CoreDNS rewrite plugin
      CoreDNS forward plugin
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