Service source

The service source creates DNS entries based on Service resources.

Filtering the Services considered

The --service-type-filter flag filters Service resources by their spec.type.
The flag may be specified multiple times to allow multiple service types.

This source supports the --label-filter flag, which filters Service resources
by a set of labels.

Domain names

The domain names of the DNS entries created from a Service are sourced from the following places:

1. Adds the domain names from any external-dns.alpha.kubernetes.io/hostname and/or
   external-dns.alpha.kubernetes.io/internal-hostname annotation.
   This behavior is suppressed if the --ignore-hostname-annotation flag was specified.

2. If no DNS entries were produced for a Service by the previous steps
   and the --compatibility flag was specified, then adds DNS entries per the
   selected compatibility mode.

3. If no DNS entries were produced for a Service by the previous steps
   or the --combine-fqdn-annotation flag was specified, then adds domain names
   generated from any--fqdn-template flag.

Domain names for headless service pods

If a headless Service (without an external-dns.alpha.kubernetes.io/target annotation) creates DNS entries with targets from
a Pod that has a non-empty spec.hostname field, additional DNS entries are created for that Pod, containing the targets from that Pod.
For each domain name created for the Service, the additional DNS entry for the Pod has that domain name prefixed with
the value of the Pod’s spec.hostname field and a ..

Targets

If the Service has an external-dns.alpha.kubernetes.io/target annotation, uses
the values from that. Otherwise, the targets of the DNS entries created from a service are sourced depending
on the Service’s spec.type:

LoadBalancer

1. If the hostname came from an external-dns.alpha.kubernetes.io/internal-hostname annotation, uses
   the Service’s spec.clusterIP field. If that field has the value None, does not generate
   any targets for the hostname.

2. Otherwise, if the Service has one or more spec.externalIPs, uses the values in that field.

3. Otherwise, iterates over each status.loadBalancer.ingress, adding any non-empty ip and/or hostname.

If the --resolve-service-load-balancer-hostname flag was specified, any non-empty hostname
is queried through DNS and any resulting IP addresses are added instead.
A DNS query failure results in zero targets being added for that load balancer’s ingress hostname.

ClusterIP (headless)

Iterates over all of the Service’s Endpoints’s subsets.addresses.
If the Service’s spec.publishNotReadyAddresses is true or the --always-publish-not-ready-addresses flag is specified,
also iterates over the Endpoints’s subsets.notReadyAddresses.

1. If an address does not target a Pod that matches the Service’s spec.selector, it is ignored.

2. If the target pod has an external-dns.alpha.kubernetes.io/target annotation, uses
   the values from that.

3. Otherwise, if the Service has an external-dns.alpha.kubernetes.io/endpoints-type: NodeExternalIP
   annotation, uses the addresses from the Pod’s Node’s status.addresses that are either of type
   ExternalIP or IPv6 addresses of type InternalIP.

4. Otherwise, if the Service has an external-dns.alpha.kubernetes.io/endpoints-type: HostIP annotation
   or the --publish-host-ip flag was specified, uses the Pod’s status.hostIP field.

5. Otherwise uses the ip field of the address from the Endpoints.

ClusterIP (not headless)

1. If the hostname came from an external-dns.alpha.kubernetes.io/internal-hostname annotation
   or the --publish-internal-services flag was specified, uses the spec.ServiceIP.

2. Otherwise, does not create any targets.

NodePort

If spec.ExternalTrafficPolicy is Local, iterates over each Node that both matches the Service’s spec.selector
and has a status.phase of Running. Otherwise iterates over all Nodes, of any phase.

Iterates over each relevant Node’s status.addresses:

1. If there is an external-dns.alpha.kubernetes.io/access: public annotation on the Service, uses both addresses with
   a type of ExternalIP and IPv6 addresses with a type of InternalIP.

2. Otherwise, if there is an external-dns.alpha.kubernetes.io/access: private annotation on the Service, uses addresses with
   a type of InternalIP.

3. Otherwise, if there is at least one address with a type of ExternalIP, uses both addresses with
   a type of ExternalIP and IPv6 addresses with a type of InternalIP.

4. Otherwise, uses addresses with a type of InternalIP.

Also iterates over the Service’s spec.ports, creating a SRV record for each port which has a nodePort.
The SRV record has a service of the Service’s name, a protocol taken from the port’s protocol field,
a priority of 0 and a weight of 50.
In order for SRV records to be created, the --managed-record-typesmust have been specified, including SRV
as one of the values.

ExternalName

Creates a target with the value of the Service’s externalName field.

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Last update: September 17, 2023