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