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    Container Compute Service:Use unmanaged CoreDNS in an ACS cluster

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    Container Compute Service:Use unmanaged CoreDNS in an ACS cluster

    Last Updated:Jun 20, 2026

    In specific scenarios, you must manually manage and maintain CoreDNS due to the highly customized requirements of the business. Alibaba Cloud Container Compute Service (ACS) clusters support unmanaged CoreDNS. This allows you to configure custom CoreDNS configurations. This topic describes how to use the unmanaged CoreDNS plug-in in an ACS cluster.

    Prerequisites

    • An ACS cluster is created. For more information, see Create an ACS cluster. If the CoreDNS plug-in is installed in the ACS cluster, uninstall the managed CoreDNS plug-in by following the installation procedure described in this topic.

    • When you create a new cluster, go to Component Configurations > Service Discovery and select Disable.

    Important

    • The unmanaged CoreDNS plug-in is an open-source standard plug-in. You are responsible for the resource costs and the O&M of the plug-in. You can resolve issues that may arise when your use the CoreDNS plug-in.

    • By default, the plug-in template provided by ACS uses the anti-affinity mechanism to distribute pods across zones. If you configured a single zone for ACS, only one replica of CoreDNS can run as expected. We recommend that you configure multiple zones to ensure disaster recovery and availability.

    Installation procedure

    1. Log on to the ACS console. In the left navigation pane, click Clusters.

    2. On the Clusters page, click the name of the target cluster. In the left navigation pane, click Add-ons.

    3. (Optional) On the Networking tab, find CoreDNS (with a Managed label) and click Uninstall. If you do not see CoreDNS (Managed) in the component list, skip this step.

      Warning

      If you uninstall CoreDNS (Managed), the Domain Name System (DNS) resolution feature of the cluster is unavailable. Make sure that business traffic does not exist in the cluster before you uninstall CoreDNS (Managed).

    4. On the Networking tab, find CoreDNS (without a Managed label) and click Install.

    5. Configure the parameters based on your requirements. After you confirm the settings, click OK to install the component.

      Important

      If you do not set the CpuRequest parameter during installation, the corresponding pod in the ACS cluster will have only 250m of available CPU resources. We recommend that you set an appropriate value for CpuRequest to avoid cluster exceptions caused by excessive load on the pod.

      The configuration form includes the following parameters: MemoryRequest (default: 100Mi), CpuRequest (default: 100m), MemoryLimit (default: 2Gi), and CpuLimit (default: empty). For NodeSelector, the default key is kubernetes.io/os and the value is linux. Tolerations is empty by default and can be configured as needed.

    6. Use kubectl to connect to the cluster and run the following command to query the pod: 

      kubectl get po -n kube-system|grep coredns

      Expected output:

      NAMESPACE     NAME                       READY   STATUS    RESTARTS   AGE
kube-system   coredns-85dc775876-sh558   1/1     Running   0          3m35s
kube-system   coredns-85dc775876-xzcpp   1/1     Running   0          3m35s

      The CoreDNS pod is started. This indicates that the unmanaged CoreDNS plug-in is installed.

    7. Run the following command in a pod in the ACS cluster to check whether the DNS resolution feature in the cluster works as expected: 

      nslookup kubernetes

      Expected output:

      Server:         10.0.0.10
Address:        10.0.0.10#53
Name:   kubernetes.default.svc.cluster.local
Address: 10.0.0.1

      The output indicates that the domain name resolution is successful and CoreDNS runs as expected.

    Custom CoreDNS configurations

    You can configure custom CoreDNS configurations by modifying the Corefile configurations, which is stored in the ACS cluster as a ConfigMap. You can directly modify the Corefile configurations to modify the CoreDNS configurations. Example:

    1. Run the following command to modify the Corefile configurations of CoreDNS: 

      kubectl -n kube-system edit cm coredns

    2. Modify the Corefile configurations of CoreDNS based on the following content: 

      Corefile: |
  .:53 {
      errors
      health {
         lameduck 15s
      }
      ready
      kubeapi
      k8s_event {
        level info error warning
      }
      kubernetes cluster.local in-addr.arpa ip6.arpa {
        pods verified
        ttl 30
        fallthrough in-addr.arpa ip6.arpa
      }
      prometheus :9153
      # forward . /etc/resolv.conf {
      # Change the forward DNS server from the default in resolv.conf to 192.168.1.10.
      forward . 192.168.1.10 {
        prefer_udp
      }
      cache 30
      log
      loop
      reload
      loadbalance
  }

      After the modification, CoreDNS automatically forwards non-cluster domain names to the DNS server whose IP address is 192.168.1.10. You can change the IP address of the DNS server based on your business requirements.

    References