How Can You Add Arbitrary Records to Kube-DNS in Kubernetes?

To add custom records to Kube-DNS in Kubernetes, we can use ConfigMaps or change the Kube-DNS deployment directly. This way, we can create our own DNS records. This helps services find each other in our Kubernetes cluster. It makes our applications work better. If we follow the right steps, our custom records will be set up and easy to access.

In this article, we will look at some ways to add custom records to Kube-DNS in Kubernetes. We will talk about understanding the Kube-DNS setup, how to use ConfigMaps for our records, using external DNS for managing records, changing the Kube-DNS deployment, checking our custom records, and answering common questions. By the end, we will know how to manage DNS records in our Kubernetes environment.

  • How to Add Arbitrary Records to Kube-DNS in Kubernetes
  • Understanding Kube-DNS Architecture for Custom Records
  • Using ConfigMap to Add Arbitrary DNS Records in Kube-DNS
  • Leveraging External DNS for Dynamic Record Management in Kube-DNS
  • Modifying Kube-DNS Deployment to Include Custom Records
  • Validating Custom DNS Records in Kube-DNS
  • Frequently Asked Questions

For more insights into Kubernetes and its parts, we can also read articles like What is Kubernetes and How Does it Simplify Container Management? and What are the Key Components of a Kubernetes Cluster?.

Understanding Kube-DNS Architecture for Custom Records

Kube-DNS is an important part of Kubernetes. It helps us find services in the cluster. It turns domain names into IP addresses. This way, pods can talk to each other using DNS names instead of fixed IP addresses.

Key Components of Kube-DNS Architecture:

  • Kube-DNS Pods: These pods are in the kube-system namespace. They handle DNS requests.
  • CoreDNS: In newer versions of Kubernetes, CoreDNS can replace Kube-DNS. It gives us more flexibility and plugins for managing DNS.
  • Etcd: Some settings and service records are kept in etcd. Kube-DNS uses etcd to find names.
  • Kube-API Server: Kube-DNS works with the Kubernetes API server. It gets service updates and keeps the DNS cache fresh.

Custom Records in Kube-DNS:

If we want to add custom DNS records, we can use the ConfigMap method. Custom records are useful for things like internal application URLs or service names that we need to reach by DNS.

Example of Kube-DNS Architecture:

apiVersion: v1
kind: Service
metadata:
  name: kube-dns
  namespace: kube-system
spec:
  selector:
    k8s-app: kube-dns
  ports:
  - name: dns
    port: 53
    protocol: UDP
  - name: dns-tcp
    port: 53
    protocol: TCP

Service Discovery Flow:

  1. A pod tries to find a service name.
  2. Kube-DNS gets the request and checks its cache.
  3. If it does not find it, it asks the Kubernetes API server.
  4. The API server gives the needed service information.
  5. Kube-DNS saves the response and sends the IP back to the pod that asked.

When we understand the Kube-DNS architecture, we can better manage and add custom DNS records for our Kubernetes setup. This setup makes it easier to discover services and improves how we communicate inside a Kubernetes cluster.

Using ConfigMap to Add Arbitrary DNS Records in Kube-DNS

We can add custom DNS records to Kube-DNS in Kubernetes by using a ConfigMap. This method helps us create our own DNS entries. Kube-DNS will then resolve these entries. Here is how we can do it:

  1. Create a ConfigMap: First, we write our DNS records in a ConfigMap YAML file. For example, if we want to add a custom A record, we can use this:
apiVersion: v1
kind: ConfigMap
metadata:
  name: custom-dns-records
  namespace: kube-system
data:
  example.com: |
    A 192.0.2.1
  1. Apply the ConfigMap: Next, we use the kubectl command to create the ConfigMap in our cluster.
kubectl apply -f custom-dns-records.yaml
  1. Modify Kube-DNS Deployment: We must update the Kube-DNS deployment to mount this ConfigMap. We edit the deployment and add a volume that points to our ConfigMap:
apiVersion: apps/v1
kind: Deployment
metadata:
  name: kube-dns
  namespace: kube-system
spec:
  template:
    spec:
      volumes:
        - name: custom-dns
          configMap:
            name: custom-dns-records
      containers:
        - name: kube-dns
          volumeMounts:
            - name: custom-dns
              mountPath: /etc/kube-dns/custom

  1. Update the DNS Configuration: We need to make sure our Kube-DNS configuration can recognize these custom records. In the Kube-DNS container, we set it to load DNS records from the path we specified.

  2. Restart Kube-DNS: After we make these changes, we restart the Kube-DNS pods to apply the new setup.

kubectl rollout restart deployment kube-dns -n kube-system
  1. Validate the DNS Records: We can check if our custom DNS records are set up correctly. We can use the dig command from inside a pod in our cluster.
kubectl run -it --rm --restart=Never dnsutils --image=busybox -- sh
# Inside the pod
dig example.com

This way, we can manage and add custom DNS records to Kube-DNS using ConfigMap. This helps our Kubernetes apps resolve custom domain names when needed. For more information about DNS in Kubernetes, we can check out how does DNS work within a Kubernetes cluster.

Leveraging External DNS for Dynamic Record Management in Kube-DNS

We can manage dynamic DNS records in Kube-DNS by using the External DNS project. This project helps us create DNS records automatically in our DNS provider based on the services and ingress resources in our Kubernetes cluster.

Prerequisites

  • We need a Kubernetes cluster that runs with Kube-DNS.
  • We must have a supported DNS provider like AWS Route 53 or Google Cloud DNS.
  • We should install External DNS in our cluster.

Installation

We can install External DNS by using Helm or applying YAML files. Here is an example with Helm:

helm repo add bitnami https://charts.bitnami.com/bitnami
helm install external-dns bitnami/external-dns \
  --set provider=aws \
  --set aws.zoneType=public \
  --set aws.assumedRole=arn:aws:iam::YOUR_AWS_ACCOUNT_ID:role/YOUR_ROLE_NAME \
  --set txtOwnerId=YOUR_OWNER_ID

We should replace YOUR_AWS_ACCOUNT_ID, YOUR_ROLE_NAME, and YOUR_OWNER_ID with our specific details.

Configuring Annotations

To let External DNS manage records, we need to add annotations to our Kubernetes Services or Ingress resources. Here is how we can annotate a Service:

apiVersion: v1
kind: Service
metadata:
  name: my-service
  annotations:
    external-dns.alpha.kubernetes.io/hostname: myapp.example.com
spec:
  type: LoadBalancer
  ports:
    - port: 80
      targetPort: 8080
  selector:
    app: my-app

Creating Ingress Resources

If we are using Ingress, we can also set up annotations to manage DNS records:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: my-ingress
  annotations:
    external-dns.alpha.kubernetes.io/hostname: myapp.example.com
spec:
  rules:
    - host: myapp.example.com
      http:
        paths:
          - path: /
            pathType: Prefix
            backend:
              service:
                name: my-service
                port:
                  number: 80

Deploying External DNS

After we configure our resources, we can deploy External DNS:

kubectl apply -f external-dns-deployment.yaml

This deployment will check for changes in the Kubernetes resources and update DNS records when needed.

Validating DNS Records

To check if our DNS records are created, we can use:

dig myapp.example.com

This command should show the IP address of our LoadBalancer service.

Using External DNS with Kube-DNS gives us a good way to manage DNS records dynamically in Kubernetes. This way, our services can always be reached through their domain names. For more information about Kubernetes DNS, we can read how does DNS work within a Kubernetes cluster.

Modifying Kube-DNS Deployment to Include Custom Records

We can modify the Kube-DNS deployment to add custom DNS records in Kubernetes by following some simple steps. This usually means changing the Kube-DNS deployment YAML file to include the needed DNS records.

  1. Edit the Kube-DNS Deployment: We can use kubectl to change the Kube-DNS deployment directly.

    kubectl edit deployment kube-dns -n kube-system

  2. Add Custom DNS Records: In the deployment spec, we need to add a ConfigMap to define the DNS records. Find the args section and set it up to use a custom dnsmasq configuration. We need to add this entry to the args:

    - --stubDomains=<your-domain>:<ip-address>

    Make sure to replace <your-domain> with your domain name and <ip-address> with the right IP address.

  3. Example Configuration: Here is a simple example of how to change the kube-dns deployment YAML:

    spec:
  containers:
  - name: kube-dns
    args:
      - --dns-port=10053
      - --dns-bind-address=0.0.0.0
      - --dns-nameservers=8.8.8.8
      - --stubDomains=example.local:10.0.0.1

  4. Apply Changes: After we edit the deployment, we should save the changes. Kubernetes will automatically restart the Kube-DNS pods to use the new setup.

  5. Verify Changes: To check if the custom records work, we can run this command:

    kubectl exec -it <kube-dns-pod-name> -n kube-system -- nslookup <your-domain>

    This should show the IP address we set for our custom DNS record.

  6. Use ConfigMap for Better Management: For better control of DNS records, we can create a ConfigMap and link it to our Kube-DNS deployment. We create a ConfigMap with our DNS records:

    apiVersion: v1
kind: ConfigMap
metadata:
  name: custom-dns-records
  namespace: kube-system
data:
  example.local: |
    10.0.0.1

    Then we change our Kube-DNS deployment to use this ConfigMap.

  7. Example of Referencing ConfigMap: We update the deployment to use the ConfigMap:

    - --stubDomains=$(CUSTOM_DNS_RECORDS)

    We also need to define the environment variable CUSTOM_DNS_RECORDS in the deployment spec.

By following these steps, we can change the Kube-DNS deployment in Kubernetes to add custom DNS records. This helps us improve our service discovery. For more information on how DNS works in a Kubernetes cluster, check this article.

Validating Custom DNS Records in Kube-DNS

We can validate custom DNS records in Kube-DNS by using the dig command. This command helps us check if the records we added work correctly.

Steps to Validate Custom DNS Records

  1. Check the DNS Configuration: We need to make sure our custom records are in the right ConfigMap or wherever we added them.

  2. Using dig Command: If we do not have the dnsutils package, we should install it. Then we can use this command to check the DNS records:

    dig @<kube-dns-ip> <your-custom-domain> A

    We replace <kube-dns-ip> with the IP address of our Kube-DNS service. We also replace <your-custom-domain> with the domain we added.

  3. Example: If we added a record for myapp.example.com, we would run:

    dig @10.96.0.10 myapp.example.com A

  4. Validating Output: We should look for the ANSWER SECTION in the output. It should show the IP address. For example:

    ;; ANSWER SECTION:
myapp.example.com.   3600 IN A 192.168.1.100

  5. Using kubectl: If we have a pod running in the cluster, we can run a command directly in the pod to check DNS resolution:

    kubectl exec -ti <pod-name> -- nslookup <your-custom-domain>

    We should replace <pod-name> with the name of our running pod.

By following these steps, we can see if the custom DNS records in Kube-DNS are working right. If we want to learn more about how Kube-DNS works, we can check this article on how does DNS work within a Kubernetes cluster.

Frequently Asked Questions

1. How can we add custom DNS records to Kube-DNS in Kubernetes?

We can add custom DNS records to Kube-DNS in Kubernetes by using a ConfigMap. A ConfigMap helps us define the DNS records we want. When we create a ConfigMap with our DNS entries, Kube-DNS will recognize and serve these records. For more steps on how to use ConfigMap for this, we can check Using ConfigMap to Add Arbitrary DNS Records in Kube-DNS.

2. What is the architecture of Kube-DNS in Kubernetes?

Kube-DNS works as a DNS server in a Kubernetes cluster. It gives name resolution services for services and pods. It has a DNS server that looks at the Kubernetes API for changes and updates the DNS records automatically. We need to understand Kube-DNS architecture to manage custom DNS records well. For more information, we can look at How does DNS work within a Kubernetes cluster?.

3. Can we use External DNS to manage DNS records in Kubernetes?

Yes, we can use External DNS to manage DNS records easily in Kubernetes. External DNS creates and manages DNS records in our DNS provider based on Kubernetes resources like services and ingresses. This makes DNS management simpler, especially in changing environments. For more details, we can visit How does Kubernetes networking work?.

4. How do we validate custom DNS records in Kube-DNS?

To check custom DNS records in Kube-DNS, we can use tools like nslookup or dig. These tools let us query the DNS records directly. When we run queries against the Kube-DNS service IP, we can see if the records we added are present and correct. This check is important to make sure our custom DNS settings work like we want.

5. What changes do we need in Kube-DNS deployment to include custom records?

To add custom records in Kube-DNS, we usually need to change the Kube-DNS deployment. We must mount the ConfigMap that has our DNS records. This means we will update the deployment YAML file to link to the ConfigMap and make sure Kube-DNS reloads the settings when we make changes. For a detailed guide on how to change deployments, we can look at How do I manage the lifecycle of a Kubernetes pod?.