Profiles
The Profile Watcher is responsible for monitoring ServiceProfile custom resources in the cluster. It triggers updates to subscribed listeners whenever a profile is added, updated, or deleted. This enables dynamic service behavior such as retries, timeouts, and routing logic to be applied to Linkerd proxies without restarting them.
func NewProfileWatcher(k8sAPI *k8s.API, log *logging.Entry) (*ProfileWatcher, error) {
watcher := &ProfileWatcher{
profileLister: k8sAPI.SP().Lister(),
profiles: make(map[ProfileID]*profilePublisher),
log: log.WithField("component", "profile-watcher"),
}
_, err := k8sAPI.SP().Informer().AddEventHandler(
cache.ResourceEventHandlerFuncs{
AddFunc: watcher.addProfile,
UpdateFunc: watcher.updateProfile,
DeleteFunc: watcher.deleteProfile,
},
)
if err != nil {
return nil, err
}
return watcher, nil
}
Each time a ServiceProfile is modified, the change is forwarded to its associated profilePublisher, which then propagates updates to all its subscribers:
func (pp *profilePublisher) subscribe(listener ProfileUpdateListener) {
pp.Lock()
defer pp.Unlock()
pp.listeners = append(pp.listeners, listener)
listener.Update(pp.profile)
pp.profileMetrics.setSubscribers(len(pp.listeners))
}
The subscriber will immediately receive the latest profile (if available), and will continue to receive updates on future changes via the Update(profile *sp.ServiceProfile) method.
kubectl logs -n linkerd linkerd-destination-6468fd7dbb-8st99 -c destination
...
time="2025-06-05T19:01:52Z" level=debug msg="Establishing watch on profile simple-app/simple-app-v1.simple-app.svc.cluster.local" addr=":8086" component=profile-watcher
time="2025-06-05T19:01:52Z" level=debug msg="Sending profile update: fully_qualified_name:\"simple-app-v1.simple-app.svc.cluster.local\" retry_budget:{retry_ratio:0.2 min_retries_per_second:10 ttl:{seconds:10}} parent_ref:{resource:{group:\"core\" kind:\"Service\" name:\"simple-app-v1\" namespace:\"simple-app\" port:80}} profile_ref:{resource:{group:\"linkerd.io\"}}" addr=":8086" component=profile-translator context-ns=simple-app context-pod=traffic-56cb8b47b8-rtn6v ns=simple-app port=80 remote="10.23.0.9:45792" svc=simple-app-v1
time="2025-06-05T19:01:51Z" level=debug msg="Stopping watch on profile simple-app/simple-app-v1.simple-app.svc.cluster.local" addr=":8086" component=profile-watcher
When a new profile is added or updated, the update(profile *sp.ServiceProfile) method is called on each listener.
func (pt *profileTranslator) update(profile *sp.ServiceProfile) {
if profile == nil {
pt.stream.Send(pt.defaultServiceProfile())
return
}
destinationProfile, err := pt.createDestinationProfile(profile)
if err != nil {
pt.log.Error(err)
return
}
pt.stream.Send(destinationProfile)
}
The update includes the routes, retry budget, and destination overrides specified in the profile. If no profile is found, it synthesizes a default profile on-the-fly like this:
func (pt *profileTranslator) defaultServiceProfile() *pb.DestinationProfile {
return &pb.DestinationProfile{
Routes: []*pb.Route{},
RetryBudget: defaultRetryBudget(),
FullyQualifiedName: pt.fullyQualifiedName,
}
}
Metrics
The Profile Watcher will also expose metrics used to track the number of subscribers to service profiles.
# HELP profile_subscribers A gauge for the current number of subscribers to a profile.
# TYPE profile_subscribers gauge
profile_subscribers{namespace="linkerd",profile="linkerd-dst-headless.linkerd.svc.cluster.local"} 2
profile_subscribers{namespace="linkerd",profile="linkerd-enterprise.linkerd.svc.cluster.local"} 10
profile_subscribers{namespace="linkerd",profile="linkerd-identity-headless.linkerd.svc.cluster.local"} 0
profile_subscribers{namespace="linkerd",profile="linkerd-policy.linkerd.svc.cluster.local"} 2
profile_subscribers{namespace="monitoring",profile="prometheus-server.monitoring.svc.cluster.local"} 2
profile_subscribers{namespace="simple-app",profile="simple-app-v1.simple-app.svc.cluster.local"} 4
# HELP profile_updates A counter for number of updates to a profile.
# TYPE profile_updates counter
profile_updates{namespace="linkerd",profile="linkerd-dst-headless.linkerd.svc.cluster.local"} 0
profile_updates{namespace="linkerd",profile="linkerd-enterprise.linkerd.svc.cluster.local"} 0
profile_updates{namespace="linkerd",profile="linkerd-identity-headless.linkerd.svc.cluster.local"} 0
profile_updates{namespace="linkerd",profile="linkerd-policy.linkerd.svc.cluster.local"} 0
profile_updates{namespace="monitoring",profile="prometheus-server.monitoring.svc.cluster.local"} 0
profile_updates{namespace="simple-app",profile="simple-app-v1.simple-app.svc.cluster.local"} 0
# HELP profile_updates_queue_overflow A counter incremented whenever the profile updates queue overflows
# TYPE profile_updates_queue_overflow counter
profile_updates_queue_overflow{fqn="linkerd-dst-headless.linkerd.svc.cluster.local",port="8086"} 0
profile_updates_queue_overflow{fqn="linkerd-enterprise.linkerd.svc.cluster.local",port="8082"} 0
profile_updates_queue_overflow{fqn="linkerd-identity-headless.linkerd.svc.cluster.local",port="8080"} 0
profile_updates_queue_overflow{fqn="linkerd-policy.linkerd.svc.cluster.local",port="8090"} 0
profile_updates_queue_overflow{fqn="prometheus-server.monitoring.svc.cluster.local",port="80"} 0
profile_updates_queue_overflow{fqn="prometheus-server.monitoring.svc.cluster.local",port="9090"} 0
profile_updates_queue_overflow{fqn="simple-app-v1.simple-app.svc.cluster.local",port="80"} 0
# HELP service_subscribers Number of subscribers to Service changes.
# TYPE service_subscribers gauge
service_subscribers{name="linkerd-dst-headless",namespace="linkerd"} 1
service_subscribers{name="linkerd-enterprise",namespace="linkerd"} 5
service_subscribers{name="linkerd-policy",namespace="linkerd"} 1
service_subscribers{name="prometheus-server",namespace="monitoring"} 1
service_subscribers{name="simple-app-v1",namespace="simple-app"} 2
