fix(multicluster)!: Link's probeSpec.period should be formatted as duration (#13586)

Before the refactoring from #13420, `link mc link` would generate a Link resource with `probeSpec.period` formatted as duration. After that change, it was generated as an integer and the service mirror was refactored as well to consume that integer and convert it into a duration. If a Link with the old semantics is consumed by a service mirror controller containing that change (or vice-versa) it will error out with "could not parse probe period". This could happen for example when re-linking as part of a multicluster upgrade, when pending the rollout the old controller would consume the upgraded Link. Or for folks upgrading just by bumping the controller image tag and not re-linking (unwise as that may be).

This fix consists on:
- Updating the Link CRD, constraining `period` to be formatted as duration
- Having the `linkerd mc link` command produce a duration value for that period, being lenient to the gateway service annotation `mirror.linkerd.io/probe-period` either using an integer (which it does by default) or a duration
- Having the probe worker consume that value as a duration

BREAKING CHANGE: this realigns behavior with edge-24.11.8, but Links generated with edge-25.1.1 would be rejected.

Author: alpeb

multicluster/charts/linkerd-multicluster/templates/link-crd.yaml

@@ -158,6 +158,7 @@ spec:
                     type: string
                   period:
                     description: Interval in between probe requests
+                    format: duration
                     type: string
                   port:
                     description: Port of remote gateway health endpoint

multicluster/cmd/link.go

@@ -7,7 +7,9 @@ import (
 	"fmt"
 	"os"
 	"path"
+	"strconv"
 	"strings"
+	"time"
 
 	"github.com/linkerd/linkerd2/controller/gen/apis/link/v1alpha2"
 	"github.com/linkerd/linkerd2/multicluster/static"
@@ -599,10 +601,21 @@ func extractProbeSpec(gateway *corev1.Service) (v1alpha2.ProbeSpec, error) {
 		return v1alpha2.ProbeSpec{}, err
 	}
 
+	// the `mirror.linkerd.io/probe-period` annotation is initialized with a
+	// default value of "3", but we require a duration-formatted string. So we
+	// perform the conversion, if required.
+	period := gateway.Annotations[k8s.GatewayProbePeriod]
+	if secs, err := strconv.ParseInt(period, 10, 64); err == nil {
+		dur := time.Duration(secs) * time.Second
+		period = dur.String()
+	} else if _, err := time.ParseDuration(period); err != nil {
+		return v1alpha2.ProbeSpec{}, fmt.Errorf("could not parse probe period: %w", err)
+	}
+
 	return v1alpha2.ProbeSpec{
 		Path:   path,
 		Port:   fmt.Sprintf("%d", port),
-		Period: gateway.Annotations[k8s.GatewayProbePeriod],
+		Period: period,
 	}, nil
 }
 

multicluster/cmd/testdata/install_default.golden

@@ -70,12 +70,11 @@ func (pw *ProbeWorker) run() {
 		pw.log.Error("Probe spec is nil")
 		return
 	}
-	probeTickerPeriodSeconds, err := strconv.ParseInt(pw.probeSpec.Period, 10, 64)
+	probeTickerPeriod, err := time.ParseDuration(pw.probeSpec.Period)
 	if err != nil {
 		pw.log.Errorf("could not parse probe period: %s", err)
 		return
 	}
-	probeTickerPeriod := time.Duration(probeTickerPeriodSeconds) * time.Second
 	maxJitter := probeTickerPeriod / 10 // max jitter is 10% of period
 	probeTicker := NewTicker(probeTickerPeriod, maxJitter)
 	defer probeTicker.Stop()