Container Service for Kubernetes:Service discovery using DNS

Index

• Notes

• How DNS resolution works in ACK Serverless clusters

• DNS service discovery solutions for ACK Serverless clusters

• FAQ

• References

Notes

• If you do not enable a DNS service discovery component when you create an ACK Serverless cluster, pods use the DNS servers provided by the Virtual Private Cloud (VPC) for domain name resolution by default. In this mode, the domain names of Kubernetes services cannot be resolved.

• For existing ACK Serverless clusters, enabling a DNS service discovery solution takes effect only on new pods. Pods created before you enable the solution do not switch their DNS configuration files. You must recreate these pods to use the new DNS service discovery solution.

• The managed CoreDNS component will gradually replace the self-managed CoreDNS component until the self-managed CoreDNS component is discontinued. The self-managed CoreDNS component may not be available in the console in the future. To use the self-managed CoreDNS component, submit a ticket for assistance.

How DNS resolution works in ACK Serverless clusters

When a pod is created in an ACK Serverless cluster, the /etc/resolv.conf file contains the following content by default. This file specifies the DNS server, search domains, and other parameters.

# The nameserver indicates the IP address of the DNS server used by this pod.
nameserver 172.xx.x.xx
# The search indicates the domain name suffixes to append when a service is requested. The following example shows the suffixes when the pod is in the kube-system namespace.
search kube-system.svc.cluster.local svc.cluster.local cluster.local
# Other parameters
options ndots:5

For more information about the fields in the DNS resolution configuration file and the Pod DNSPolicy, see DNS principles and configurations.

DNS service discovery solutions for ACK Serverless clusters

FAQ

How can I check whether the managed CoreDNS, self-managed CoreDNS, or PrivateZone component is enabled for my cluster?

• Managed CoreDNS and self-managed CoreDNS components

  Log on to the Container Service Management Console. On the cluster management page, select Operations Management > Component Management and click the Network tab. If the Installed label is displayed in the upper-right corner of a component, this indicates that the managed CoreDNS or self-managed CoreDNS component is enabled for the cluster.

  The following figure shows an example of the managed CoreDNS component.

  

• PrivateZone component

  Log on to the PrivateZone console. On the Authoritative Zones On VPC tab, search for a Domain Zone by cluster ID. If you find a zone whose name ends with the cluster ID, this indicates that the PrivateZone component is enabled.

How can I check whether an application pod is using the managed CoreDNS, self-managed CoreDNS, or PrivateZone component?

• Managed CoreDNS and self-managed CoreDNS components

  Run the kubectl exec command to enter the pod. Run the cat /etc/resolv.conf command. If the nameserver field is set to the cluster IP address of the kube-dns service in the kube-system namespace, the pod is using the managed CoreDNS or self-managed CoreDNS component.

• PrivateZone component

  Run the kubectl exec command to enter the pod. Run the cat /etc/resolv.conf command. If the nameserver field is set to 100.100.2.136 and 100.100.2.138, the pod is using the PrivateZone component. The IP addresses in this example are for reference only. Use the actual IP addresses.

References

• DNS principles and configurations

• DNS best practices