ExternalDNS

ExternalDNS

In this section we provide examples for the most common use-cases of ExternalDNS with F5 CIS:

• Publish FQDN

ExternalDNS is a Kubernetes add-on that allows you to control DNS records of F5 DNS servers with information about exposed Kubernetes services through VirtualServer, TransportServer or IngressLink CRDs.

To run the demos, use the terminal on VS Code. VS Code is under the bigip-01 on the Access drop-down menu. Click here to see how.

How does it work

ExternalDNS has on its specification the host parameter that defines the FQDN that user wants to publish. In order for CIS to establish a link between the ExternalDNS resources, that holds the wideIP information, and the VirtualServer, that holds the IP that the users should connect to, it looks for a match on Host parameter that exists on both resources. If a match is established, then CIS creates a wideIP on F5 DNS with the pool member IP being the VirtualServer IP address. The same applies for TransportServer and IngressLink.

In the following manifests you can see the host parameter on VirtualServer matching the host parameter on ExternalDNS.

apiVersion: cis.f5.com/v1
kind: VirtualServer
metadata:
  labels:
    f5cr: "true"
  name: sample-virtual
spec:
  host: www.f5demo.cloud       <==== Hostname (FQDN)
  virtualServerAddress: 10.1.10.240
  pools:
  - monitor:
      interval: 20
      recv: ""
      send: /
      timeout: 10
      type: http
    path: /
    service: svc-1
    servicePort: 80

An ExternalDNS Custom Resource must be created that will have the same hostname as with Custom Resource (VS/TS/IL) we created earlier.

apiVersion: "cis.f5.com/v1"
kind: ExternalDNS
metadata:
  name: exdns
  labels:
    f5cr: "true"
spec:
  domainName: www.f5demo.cloud     <==== Hostname matches with pervious CR
  dnsRecordType: A
  loadBalanceMethod: round-robin
  pools:
  - name: www-primary-k8s
    dnsRecordType: A
    loadBalanceMethod: round-robin
    dataServerName: /Common/GSLBServer
    monitor:
      type: https
      send: "GET /"
      recv: ""
      interval: 10
      timeout: 10

Note: The dataServerName parameter, which in the above example has the value of /Common/GSLBServer referes to the BIGIP device that holds the VirtualServer that has been confiured through the CRDs. This is to be manual configured prior to the ExternalDNS configuration. More information on ExternalDNS can be found on here

Publish FQDN

This section demonstrates how publish a DNS records of a service that is publish with TransportServer resource.

Eg: tcp-transport-server.yml

apiVersion: "cis.f5.com/v1"
kind: TransportServer
metadata:
  labels:
    f5cr: "true"
  name: edns-app1
spec:
  ipamLabel: "prod"
  host: edns.f5demo.local       <===== Hostname
  virtualServerPort: 80
  virtualServerName: edns-app1
  mode: standard
  snat: auto
  pool:
    service: app1-svc
    servicePort: 8080
    monitor:
      type: tcp
      interval: 3
      timeout: 10

Create the Application deployment and service:

kubectl apply -f ~/oltra/setup/apps/apps.yml

Change the working directory to TransportServer.

cd ~/oltra/use-cases/cis-examples/cis-crd/ExternalDNS

Deploy TransportServer for app1-svc with host vaule of edns.f5demo.local.

kubectl apply -f ts-fqdn.yml

Confirm that the TS CRD is deployed correctly. You should see Ok under the Status column for the TransportServer that was just deployed.

kubectl get f5-ts edns-app1

Save the IP adresses that was assigned by the IPAM for this TS

IP=$(kubectl get f5-ts edns-app1 --output=jsonpath='{.status.vsAddress}')

Try accessing the service as per the example below.

curl http://$IP/

The output should be similar to:

Server address: 10.244.140.103:8080
Server name: app1-6cc75dfc85-qhk5d
Date: 14/Jul/2022:06:17:19 +0000
URI: /
Request ID: 18c2b70bcca18c590a0125db04be5661

Create the EDNS resource to publish edns.f5demo.local on F5 DNS

kubectl apply -f edns-fqdn.yml

Resolve the IP address through DNS

dig @10.1.10.200 gslb.f5demo.local +short

Save the IP adresses that was resolved through DNS

DNS_IP=$(dig @10.1.10.200 gslb.f5demo.local +short)

Try accessing the service as per the example below.

curl http://$DNS_IP/

The output should be similar to:

Server address: 10.244.140.103:8080
Server name: app1-6cc75dfc85-qhk5d
Date: 14/Jul/2022:06:17:19 +0000
URI: /
Request ID: 18c2b70bcca18c590a0125db04be5661

Clean up the environment (Optional)

kubectl delete -f ts-fqdn.yml
kubectl delete -f edns-fqdn.yml