NodeLocal DNSCache

Introduction

NodeLocal DNSCache is an add-on developed based on the community NodeLocal DNSCache. This add-on functions as a DaemonSet to run the DNS cache proxy on cluster nodes to improve cluster DNS performance.

Open source community: https://github.com/kubernetes/dns

After NodeLocal DNSCache is enabled, a DNS query goes through the path as shown below.

Figure 1 NodeLocal DNSCache query path

Notes and Constraints

• This feature is available only to clusters of v1.19 or later.

Installing the Add-on

1. Log in to the CCE console and click the cluster name to access the cluster console. Choose Add-ons in the navigation pane, locate NodeLocal DNSCache on the right, and click Install.
2. On the Install Add-on page, configure the specifications.

   Table 1 Add-on configuration

   Parameter	Description
   Add-on Specifications	Select Standalone, HA, or Custom for Add-on Specifications.
   Pods	Number of pods that will be created to match the selected add-on specifications. If you select Custom, you can adjust the number of pods as required. High availability is not possible with a single pod. If an error occurs on the node where the add-on instance runs, the add-on will fail.
   Containers	CPU and memory quotas of the container allowed for the selected add-on specifications. If you select Custom, you can adjust the container specifications as required.

3. Configure the add-on parameters.
   • DNSConfig Automatic Injection: After this function is enabled, a DNSConfig admission controller will be created. The controller intercepts pod creation requests in the namespace labeled with node-localdns-injection=enabled based on admission webhooks and automatically configures DNSConfig for pods. If this function is disabled or the pod belongs to a non-target namespace, you must manually configure DNSConfig for the pod.
     After automatic injection is enabled, you can customize the following configuration items for DNSConfig (supported when the add-on version is 1.6.7 or later):

     

     If DNSConfig has been configured in the pod when automatic injection is enabled, DNSConfig in the pod will be used first.

     • IP Address of DNS Server (optional): IP address list of the DNS server obtained when the container resolves the domain name. NodeLocal DNSCache and CoreDNS IP addresses are added by default. You have the option to add an additional IP address, but duplicates will be removed.
     • Search Domain (optional): a search list for host-name lookup. When a domain name cannot be resolved, DNS queries will be attempted combining the domain name with each domain in the search list in turn until a match is found or all domains in the search list are tried. You can add up to three extra search domains, but any duplicates will be removed.
     • ndots: specifies that if a domain name has fewer periods (.) than the specified value of ndots, it will be combined with the search domain list for DNS query. If the domain name still cannot be resolved, it will be used for DNS query. The system will perform a DNS query on a domain name if the number of periods (.) in it is greater than or equal to the value of ndots. If the domain name cannot be resolved correctly, the system will sequentially combine it with the search domain list and then perform a DNS query.
   • Target Namespace: This parameter is available after DNSConfig Automatic Injection is enabled. Only NodeLocal DNSCache of v1.3.0 or later supports this function.
     • All Enabled: CCE adds the node-local-dns-injection=enabled label to all created namespaces excluding built-in ones (such as kube-system), identifies namespace creation requests, and automatically adds the label to newly created namespaces.
     • Manual configuration: You must manually add the node-local-dns-injection=enabled label to the namespaces requiring the injection of DNSConfig. For details, see Managing Namespace Labels.

4. Configure scheduling policies for the add-on.
   

   • Scheduling policies do not take effect on add-on instances of the DaemonSet type.
   • When configuring multi-AZ deployment or node affinity, ensure that there are nodes meeting the scheduling policy and that resources are sufficient in the cluster. Otherwise, the add-on cannot run.

   Table 2 Configurations for add-on scheduling

   Parameter	Description
   Multi AZ	Preferred: Deployment pods of the add-on will be preferentially scheduled to nodes in different AZs. If all the nodes in the cluster are deployed in the same AZ, the pods will be scheduled to that AZ. Equivalent mode: Deployment pods of the add-on are evenly scheduled to the nodes in the cluster in each AZ. If a new AZ is added, you are advised to increase add-on pods for cross-AZ HA deployment. With the Equivalent multi-AZ deployment, the difference between the number of add-on pods in different AZs will be less than or equal to 1. If resources in one of the AZs are insufficient, pods cannot be scheduled to that AZ. Required: Deployment pods of the add-on will be forcibly scheduled to nodes in different AZs. If there are fewer AZs than pods, the extra pods will fail to run.
   Node Affinity	Not configured: Node affinity is disabled for the add-on. Node Affinity: Specify the nodes where the add-on is deployed. If you do not specify the nodes, the add-on will be randomly scheduled based on the default cluster scheduling policy. Specified Node Pool Scheduling: Specify the node pool where the add-on is deployed. If you do not specify the node pool, the add-on will be randomly scheduled based on the default cluster scheduling policy. Custom Policies: Enter the labels of the nodes where the add-on is to be deployed for more flexible scheduling policies. If you do not specify node labels, the add-on will be randomly scheduled based on the default cluster scheduling policy. If multiple custom affinity policies are configured, ensure that there are nodes that meet all the affinity policies in the cluster. Otherwise, the add-on cannot run.
   Toleration	Using both taints and tolerations allows (not forcibly) the add-on Deployment to be scheduled to a node with the matching taints, and controls the Deployment eviction policies after the node where the Deployment is located is tainted. The add-on adds the default tolerance policy for the node.kubernetes.io/not-ready and node.kubernetes.io/unreachable taints, respectively. The tolerance time window is 60s. For details, see Configuring Tolerance Policies.

5. Click Install.

Components

Using NodeLocal DNSCache

By default, application requests are sent through the CoreDNS proxy. To use node-local-dns as the DNS cache proxy, use any of the following methods:

• Auto injection: Automatically configure the dnsConfig field of the pod when creating the pod. (This function is not available for pods in system namespaces such as kube-system.)
• Manual configuration: Manually configure the dnsConfig field of the pod.

Auto injection

The following conditions must be met:

• Automatic DNSConfig injection has been enabled during the add-on installation.
• The node-local-dns-injection=enabled label has been added to the namespace. For example, run the following command to add the label to the default namespace:

  kubectl label namespace default node-local-dns-injection=enabled

• The new pod does not run in system namespaces such as kube-system and kube-public namespace.
• The node-local-dns-injection=disabled label for disabling DNS injection is not added to the new pod.
• The new pod's DNSPolicy is ClusterFirstWithHostNet. Alternatively, the pod does not use the host network and DNSPolicy is ClusterFirst.

After auto injection is enabled, the following dnsConfig settings are automatically added to the created pod. In addition to the NodeLocal DNSCache address 169.254.20.10, the CoreDNS address 10.247.3.10 is added to nameservers, ensuring high availability of the service DNS server.

...
  dnsConfig:
    nameservers:
      - 169.254.20.10
      - 10.247.3.10
    searches:
      - default.svc.cluster.local
      - svc.cluster.local
      - cluster.local
    options:
      - name: timeout
        value: ''
      - name: ndots
        value: '5'
      - name: single-request-reopen
...

Manual configuration

Manually add the dnsConfig settings to the pod.

Create a pod and add the NodeLocal DNSCache IP address 169.254.20.10 to the DNSConfig nameservers configuration.

apiVersion: v1
kind: Pod
metadata:
  name: nginx
spec:
  containers:
  - image: nginx:alpine
    name: container-0
  dnsConfig:
    nameservers:
    - 169.254.20.10
    - 10.247.3.10
    searches:
    - default.svc.cluster.local
    - svc.cluster.local
    - cluster.local
    options:
    - name: ndots
      value: '2'
  imagePullSecrets:
  - name: default-secret

Uninstalling the Add-on

Uninstalling the add-on will affect the pods that have used the node-local-dns address for domain name resolution. Before uninstalling the add-on, delete the node-local-dns-injection=enabled label from the involved namespaces, and delete and recreate the pods with this label.

1. Check the add-on.
   1. Log in to the CCE console and click the cluster name to access the cluster console. Choose Add-ons in the navigation pane, locate NodeLocal DNSCache on the right, and click Edit.
   2. In the Parameters area, check whether DNSConfig Automatic Injection is enabled.
      If DNSConfig Automatic Injection has been enabled:

      1. In the navigation pane, choose Namespaces.
      2. Locate the rows that contain the namespaces with the node-local-dns-injection=enabled label and delete the label. For details, see Managing Namespace Labels.
      3. Delete the pods in these namespaces and recreate pods.

      If DNSConfig Automatic Injection has not been enabled:

      1. Use kubectl to access the cluster.
      2. Check the pods with DNSConfig manually injected. If multiple namespaces are involved, check all the pods in these namespaces.

         For example, to check pods in the default namespace, run the following command:

         kubectl get pod -n default -o yaml

      3. Manually remove DNSConfig and recreate pods.

2. Uninstall NodeLocal DNSCache.
   1. In the navigation pane, choose Add-ons. Locate NodeLocal DNSCache and click Uninstall.
   2. In the displayed dialog box, click Yes.

Helpful Links

Using NodeLocal DNSCache to Improve DNS Performance