Setting up ExternalDNS for Services on OpenStack Designate¶
This tutorial describes how to setup ExternalDNS for usage within a Kubernetes cluster using OpenStack Designate DNS.
Authenticating with OpenStack¶
We are going to use OpenStack CLI - openstack utility, which is an umbrella application for most of OpenStack clients including designate.
All OpenStack CLIs require authentication parameters to be provided. These parameters include:
* URL of the OpenStack identity service (keystone) which is responsible for user authentication and also served as a registry for other
OpenStack services. Designate endpoints must be registered in keystone in order to ExternalDNS and OpenStack CLI be able to find them.
* OpenStack region name
* User login name.
* User project (tenant) name.
* User domain (only when using keystone API v3)
Although these parameters can be passed explicitly through the CLI flags, traditionally it is done by sourcing openrc file (source ~/openrc) that is a
shell snippet that sets environment variables that all OpenStack CLI understand by convention.
Recent versions of OpenStack Dashboard have a nice UI to download openrc file for both v2 and v3 auth protocols. Both protocols can be used with ExternalDNS.
v3 is generally preferred over v2, but might not be available in some OpenStack installations.
Installing OpenStack Designate¶
Please refer to the Designate deployment tutorial for instructions on how
to install and test Designate with BIND backend. You will be required to have admin rights in existing OpenStack installation to do this. One convenient
way to get yourself an OpenStack installation to play with is to use DevStack.
Creating DNS zones¶
All domain names that are ExternalDNS is going to create must belong to one of DNS zones created in advance. Here is an example of how to create example.com DNS zone:
It is important to manually create all the zones that are going to be used for kubernetes entities (ExternalDNS sources) before starting ExternalDNS.
Deploy ExternalDNS¶
Create a deployment file called externaldns.yaml with the following contents:
Manifest (for clusters without RBAC enabled)¶
apiVersion: apps/v1
kind: Deployment
metadata:
name: external-dns
spec:
strategy:
type: Recreate
selector:
matchLabels:
app: external-dns
template:
metadata:
labels:
app: external-dns
spec:
containers:
- name: external-dns
image: k8s.gcr.io/external-dns/external-dns:v0.7.6
args:
- --source=service # ingress is also possible
- --domain-filter=example.com # (optional) limit to only example.com domains; change to match the zone created above.
- --provider=designate
env: # values from openrc file
- name: OS_AUTH_URL
value: https://controller/identity/v3
- name: OS_REGION_NAME
value: RegionOne
- name: OS_USERNAME
value: admin
- name: OS_PASSWORD
value: p@ssw0rd
- name: OS_PROJECT_NAME
value: demo
- name: OS_USER_DOMAIN_NAME
value: Default
Manifest (for clusters with RBAC enabled)¶
apiVersion: v1
kind: ServiceAccount
metadata:
name: external-dns
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
name: external-dns
rules:
- apiGroups: [""]
resources: ["services","endpoints","pods"]
verbs: ["get","watch","list"]
- apiGroups: [""]
resources: ["pods"]
verbs: ["get","watch","list"]
- apiGroups: ["extensions","networking.k8s.io"]
resources: ["ingresses"]
verbs: ["get","watch","list"]
- apiGroups: [""]
resources: ["nodes"]
verbs: ["watch","list"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
name: external-dns-viewer
roleRef:
apiGroup: rbac.authorization.k8s.io
kind: ClusterRole
name: external-dns
subjects:
- kind: ServiceAccount
name: external-dns
namespace: default
---
apiVersion: apps/v1
kind: Deployment
metadata:
name: external-dns
spec:
selector:
matchLabels:
app: external-dns
strategy:
type: Recreate
template:
metadata:
labels:
app: external-dns
spec:
serviceAccountName: external-dns
containers:
- name: external-dns
image: k8s.gcr.io/external-dns/external-dns:v0.7.6
args:
- --source=service # ingress is also possible
- --domain-filter=example.com # (optional) limit to only example.com domains; change to match the zone created above.
- --provider=designate
env: # values from openrc file
- name: OS_AUTH_URL
value: https://controller/identity/v3
- name: OS_REGION_NAME
value: RegionOne
- name: OS_USERNAME
value: admin
- name: OS_PASSWORD
value: p@ssw0rd
- name: OS_PROJECT_NAME
value: demo
- name: OS_USER_DOMAIN_NAME
value: Default
Create the deployment for ExternalDNS:
Optional: Trust self-sign certificates¶
If your OpenStack-Installation is configured with a self-sign certificate, you could extend the pod.spec with following secret-mount:
volumeMounts:
- mountPath: /etc/ssl/certs/
name: cacerts
volumes:
- name: cacerts
secret:
defaultMode: 420
secretName: self-sign-certs
content of the secret self-sign-certs must be the certificate/chain in PEM format.
Deploying an Nginx Service¶
Create a service file called ‘nginx.yaml’ with the following contents:
apiVersion: apps/v1
kind: Deployment
metadata:
name: nginx
spec:
selector:
matchLabels:
app: nginx
template:
metadata:
labels:
app: nginx
spec:
containers:
- image: nginx
name: nginx
ports:
- containerPort: 80
---
apiVersion: v1
kind: Service
metadata:
name: nginx
annotations:
external-dns.alpha.kubernetes.io/hostname: my-app.example.com
spec:
selector:
app: nginx
type: LoadBalancer
ports:
- protocol: TCP
port: 80
targetPort: 80
Note the annotation on the service; use the same hostname as the DNS zone created above.
ExternalDNS uses this annotation to determine what services should be registered with DNS. Removing the annotation will cause ExternalDNS to remove the corresponding DNS records.
Create the deployment and service:
Once the service has an external IP assigned, ExternalDNS will notice the new service IP address and notify Designate,
which in turn synchronize DNS records with underlying DNS server backend.
Verifying DNS records¶
To verify that DNS record was indeed created, you can use the following command:
There should be a record for my-app.example.com having ACTIVE status. And of course, the ultimate method to verify is to issue a DNS query:
Cleanup¶
Now that we have verified that ExternalDNS created all DNS records, we can delete the tutorial’s example: