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402 lines
12 KiB
Markdown
402 lines
12 KiB
Markdown
# Configuring RFC2136 provider
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This tutorial describes how to use the RFC2136 with either BIND or Windows DNS.
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## Using with BIND
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To use external-dns with BIND: generate/procure a key, configure DNS and add a
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deployment of external-dns.
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### Server credentials:
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- RFC2136 was developed for and tested with
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[BIND](https://www.isc.org/downloads/bind/) DNS server. This documentation
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assumes that you already have a configured and working server. If you don't,
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please check BIND documents or tutorials.
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- If your DNS is provided for you, ask for a TSIG key authorized to update and
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transfer the zone you wish to update. The key will look something like below.
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Skip the next steps wrt BIND setup.
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```text
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key "externaldns-key" {
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algorithm hmac-sha256;
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secret "96Ah/a2g0/nLeFGK+d/0tzQcccf9hCEIy34PoXX2Qg8=";
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};
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```
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- If you are your own DNS administrator create a TSIG key. Use
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`tsig-keygen -a hmac-sha256 externaldns` or on older distributions
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`dnssec-keygen -a HMAC-SHA256 -b 256 -n HOST externaldns`. You will end up with
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a key printed to standard out like above (or in the case of dnssec-keygen in a
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file called `Kexternaldns......key`).
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### BIND Configuration:
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If you do not administer your own DNS, skip to RFC provider configuration
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- Edit your named.conf file (or appropriate included file) and add/change the
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following.
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- Make sure You are listening on the right interfaces. At least whatever
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interface external-dns will be communicating over and the interface that
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faces the internet.
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- Add the key that you generated/was given to you above. Copy paste the four
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lines that you got (not the same as the example key) into your file.
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- Create a zone for kubernetes. If you already have a zone, skip to the next
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step. (I put the zone in it's own subdirectory because named,
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which shouldn't be running as root, needs to create a journal file and the
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default zone directory isn't writeable by named).
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```text
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zone "k8s.example.org" {
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type master;
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file "/etc/bind/pri/k8s/k8s.zone";
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};
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```
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- Add your key to both transfer and update. For instance with our previous
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zone.
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```text
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zone "k8s.example.org" {
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type master;
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file "/etc/bind/pri/k8s/k8s.zone";
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allow-transfer {
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key "externaldns-key";
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};
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update-policy {
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grant externaldns-key zonesub ANY;
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};
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};
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```
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- Create a zone file (k8s.zone):
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```text
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$TTL 60 ; 1 minute
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k8s.example.org IN SOA k8s.example.org. root.k8s.example.org. (
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16 ; serial
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60 ; refresh (1 minute)
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60 ; retry (1 minute)
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60 ; expire (1 minute)
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60 ; minimum (1 minute)
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)
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NS ns.k8s.example.org.
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ns A 123.456.789.012
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```
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- Reload (or restart) named
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### Using external-dns
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To use external-dns add an ingress or a LoadBalancer service with a host that
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is part of the domain-filter. For example both of the following would produce
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A records.
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```text
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apiVersion: v1
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kind: Service
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metadata:
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name: nginx
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annotations:
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external-dns.alpha.kubernetes.io/hostname: svc.example.org
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spec:
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type: LoadBalancer
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ports:
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- port: 80
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targetPort: 80
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selector:
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app: nginx
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---
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apiVersion: networking.k8s.io/v1
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kind: Ingress
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metadata:
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name: my-ingress
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spec:
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rules:
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- host: ingress.example.org
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http:
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paths:
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- path: /
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backend:
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serviceName: my-service
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servicePort: 8000
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```
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### Custom TTL
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The default DNS record TTL (Time-To-Live) is 0 seconds. You can customize this value by setting the annotation `external-dns.alpha.kubernetes.io/ttl`. e.g., modify the service manifest YAML file above:
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```
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apiVersion: v1
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kind: Service
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metadata:
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name: nginx
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annotations:
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external-dns.alpha.kubernetes.io/hostname: nginx.external-dns-test.my-org.com
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external-dns.alpha.kubernetes.io/ttl: 60
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spec:
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...
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```
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This will set the DNS record's TTL to 60 seconds.
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A default TTL for all records can be set using the the flag with a time in seconds, minutes or hours, such as `--rfc2136-min-ttl=60s`
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There are other annotation that can affect the generation of DNS records, but these are beyond the scope of this
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tutorial and are covered in the main documentation.
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### Test with external-dns installed on local machine (optional)
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You may install external-dns and test on a local machine by running:
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```external-dns --txt-owner-id k8s --provider rfc2136 --rfc2136-host=192.168.0.1 --rfc2136-port=53 --rfc2136-zone=k8s.example.org --rfc2136-tsig-secret=96Ah/a2g0/nLeFGK+d/0tzQcccf9hCEIy34PoXX2Qg8= --rfc2136-tsig-secret-alg=hmac-sha256 --rfc2136-tsig-keyname=externaldns-key --rfc2136-tsig-axfr --source ingress --once --domain-filter=k8s.example.org --dry-run```
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- host should be the IP of your master DNS server.
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- tsig-secret should be changed to match your secret.
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- tsig-keyname needs to match the keyname you used (if you changed it).
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- domain-filter can be used as shown to filter the domains you wish to update.
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### RFC2136 provider configuration:
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In order to use external-dns with your cluster you need to add a deployment
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with access to your ingress and service resources. The following are two
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example manifests with and without RBAC respectively.
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- With RBAC:
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```text
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apiVersion: v1
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kind: Namespace
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metadata:
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name: external-dns
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labels:
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name: external-dns
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---
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apiVersion: rbac.authorization.k8s.io/v1
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kind: ClusterRole
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metadata:
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name: external-dns
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namespace: external-dns
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rules:
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- apiGroups:
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- ""
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resources:
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- services
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- endpoints
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- pods
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- nodes
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verbs:
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- get
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- watch
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- list
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- apiGroups:
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- extensions
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- networking.k8s.io
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resources:
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- ingresses
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verbs:
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- get
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- list
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- watch
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---
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apiVersion: v1
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kind: ServiceAccount
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metadata:
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name: external-dns
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namespace: external-dns
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---
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apiVersion: rbac.authorization.k8s.io/v1
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kind: ClusterRoleBinding
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metadata:
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name: external-dns-viewer
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namespace: external-dns
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roleRef:
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apiGroup: rbac.authorization.k8s.io
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kind: ClusterRole
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name: external-dns
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subjects:
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- kind: ServiceAccount
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name: external-dns
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namespace: external-dns
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---
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apiVersion: apps/v1
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kind: Deployment
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metadata:
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name: external-dns
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namespace: external-dns
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spec:
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selector:
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matchLabels:
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app: external-dns
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template:
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metadata:
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labels:
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app: external-dns
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spec:
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serviceAccountName: external-dns
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containers:
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- name: external-dns
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image: registry.k8s.io/external-dns/external-dns:v0.13.1
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args:
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- --registry=txt
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- --txt-prefix=external-dns-
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- --txt-owner-id=k8s
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- --provider=rfc2136
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- --rfc2136-host=192.168.0.1
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- --rfc2136-port=53
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- --rfc2136-zone=k8s.example.org
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- --rfc2136-tsig-secret=96Ah/a2g0/nLeFGK+d/0tzQcccf9hCEIy34PoXX2Qg8=
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- --rfc2136-tsig-secret-alg=hmac-sha256
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- --rfc2136-tsig-keyname=externaldns-key
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- --rfc2136-tsig-axfr
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- --source=ingress
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- --domain-filter=k8s.example.org
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```
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- Without RBAC:
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```text
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apiVersion: v1
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kind: Namespace
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metadata:
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name: external-dns
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labels:
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name: external-dns
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---
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apiVersion: apps/v1
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kind: Deployment
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metadata:
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name: external-dns
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namespace: external-dns
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spec:
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selector:
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matchLabels:
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app: external-dns
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template:
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metadata:
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labels:
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app: external-dns
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spec:
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containers:
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- name: external-dns
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image: registry.k8s.io/external-dns/external-dns:v0.13.1
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args:
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- --registry=txt
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- --txt-prefix=external-dns-
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- --txt-owner-id=k8s
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- --provider=rfc2136
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- --rfc2136-host=192.168.0.1
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- --rfc2136-port=53
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- --rfc2136-zone=k8s.example.org
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- --rfc2136-tsig-secret=96Ah/a2g0/nLeFGK+d/0tzQcccf9hCEIy34PoXX2Qg8=
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- --rfc2136-tsig-secret-alg=hmac-sha256
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- --rfc2136-tsig-keyname=externaldns-key
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- --rfc2136-tsig-axfr
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- --source=ingress
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- --domain-filter=k8s.example.org
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```
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## Microsoft DNS (Insecure Updates)
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While `external-dns` was not developed or tested against Microsoft DNS, it can be configured to work against it. YMMV.
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### Insecure Updates
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#### DNS-side configuration
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1. Create a DNS zone
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2. Enable insecure dynamic updates for the zone
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3. Enable Zone Transfers to all servers
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#### `external-dns` configuration
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You'll want to configure `external-dns` similarly to the following:
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```text
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...
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- --provider=rfc2136
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- --rfc2136-host=192.168.0.1
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- --rfc2136-port=53
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- --rfc2136-zone=k8s.example.org
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- --rfc2136-insecure
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- --rfc2136-tsig-axfr # needed to enable zone transfers, which is required for deletion of records.
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...
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```
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### Secure Updates Using RFC3645 (GSS-TSIG)
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### DNS-side configuration
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1. Create a DNS zone
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2. Enable secure dynamic updates for the zone
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3. Enable Zone Transfers to all servers
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If you see any error messages which indicate that `external-dns` was somehow not able to fetch
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existing DNS records from your DNS server, this could mean that you forgot about step 3.
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#### Kerberos Configuration
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DNS with secure updates relies upon a valid Kerberos configuration running within the `external-dns` container. At this time, you will need to create a ConfigMap for the `external-dns` container to use and mount it in your deployment. Below is an example of a working Kerberos configuration inside a ConfigMap definition. This may be different depending on many factors in your environment:
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```yaml
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apiVersion: v1
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kind: ConfigMap
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metadata:
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creationTimestamp: null
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name: krb5.conf
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data:
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krb5.conf: |
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[logging]
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default = FILE:/var/log/krb5libs.log
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kdc = FILE:/var/log/krb5kdc.log
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admin_server = FILE:/var/log/kadmind.log
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[libdefaults]
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dns_lookup_realm = false
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ticket_lifetime = 24h
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renew_lifetime = 7d
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forwardable = true
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rdns = false
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pkinit_anchors = /etc/pki/tls/certs/ca-bundle.crt
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default_ccache_name = KEYRING:persistent:%{uid}
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default_realm = YOUR-REALM.COM
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[realms]
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YOUR-REALM.COM = {
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kdc = dc1.yourdomain.com
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admin_server = dc1.yourdomain.com
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}
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[domain_realm]
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yourdomain.com = YOUR-REALM.COM
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.yourdomain.com = YOUR-REALM.COM
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```
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In most cases, the realm name will probably be the same as the domain name, so you can simply replace
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`YOUR-REALM.COM` with something like `YOURDOMAIN.COM`.
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Once the ConfigMap is created, the container `external-dns` container needs to be told to mount that ConfigMap as a volume at the default Kerberos configuration location. The pod spec should include a similar configuration to the following:
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```yaml
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...
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volumeMounts:
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- mountPath: /etc/krb5.conf
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name: kerberos-config-volume
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subPath: krb5.conf
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...
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volumes:
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- configMap:
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defaultMode: 420
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name: krb5.conf
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name: kerberos-config-volume
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...
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```
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#### `external-dns` configuration
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You'll want to configure `external-dns` similarly to the following:
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```text
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...
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- --provider=rfc2136
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- --rfc2136-gss-tsig
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- --rfc2136-host=dns-host.yourdomain.com
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- --rfc2136-port=53
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- --rfc2136-zone=your-zone.com
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- --rfc2136-kerberos-username=your-domain-account
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- --rfc2136-kerberos-password=your-domain-password
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- --rfc2136-kerberos-realm=your-domain.com
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- --rfc2136-tsig-axfr # needed to enable zone transfers, which is required for deletion of records.
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...
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```
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As noted above, the `--rfc2136-kerberos-realm` flag is completely optional and won't be necessary in many cases.
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Most likely, you will only need it if you see errors similar to this: `KRB Error: (68) KDC_ERR_WRONG_REALM Reserved for future use`.
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The flag `--rfc2136-host` can be set to the host's domain name or IP address.
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However, it also determines the name of the Kerberos principal which is used during authentication.
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This means that Active Directory might only work if this is set to a specific domain name, possibly leading to errors like this:
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`KDC_ERR_S_PRINCIPAL_UNKNOWN Server not found in Kerberos database`.
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To fix this, try setting `--rfc2136-host` to the "actual" hostname of your DNS server.
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