Add passive health checks

pkg/server/service/service.go

@@ -341,7 +341,7 @@ func (m *Manager) getLoadBalancerServiceHandler(ctx context.Context, serviceName
 	var lb serverBalancer
 	switch service.Strategy {
 	// Here we are handling the empty value to comply with providers that are not applying defaults (e.g. REST provider)
-	// TODO: remove this when all providers apply default values.
+	// TODO: remove this empty check when all providers apply default values.
 	case dynamic.BalancerStrategyWRR, "":
 		lb = wrr.New(service.Sticky, service.HealthCheck != nil)
 	case dynamic.BalancerStrategyP2C:
@@ -350,6 +350,17 @@ func (m *Manager) getLoadBalancerServiceHandler(ctx context.Context, serviceName
 		return nil, fmt.Errorf("unsupported load-balancer strategy %q", service.Strategy)
 	}
 
+	var passiveHealthChecker *healthcheck.PassiveServiceHealthChecker
+	if service.PassiveHealthCheck != nil {
+		passiveHealthChecker = healthcheck.NewPassiveHealthChecker(
+			serviceName,
+			lb,
+			service.PassiveHealthCheck.MaxFailedAttempts,
+			service.PassiveHealthCheck.FailureWindow,
+			service.HealthCheck != nil,
+			m.observabilityMgr.MetricsRegistry())
+	}
+
 	healthCheckTargets := make(map[string]*url.URL)
 
 	for i, server := range shuffle(service.Servers, m.rand) {
@@ -368,6 +379,11 @@ func (m *Manager) getLoadBalancerServiceHandler(ctx context.Context, serviceName
 			return nil, fmt.Errorf("error building proxy for server URL %s: %w", server.URL, err)
 		}
 
+		if passiveHealthChecker != nil {
+			// If passive health check is enabled, we wrap the proxy with the passive health checker.
+			proxy = passiveHealthChecker.WrapHandler(ctx, proxy, target.String())
+		}
+
 		// The retry wrapping must be done just before the proxy handler,
 		// to make sure that the retry will not be triggered/disabled by
 		// middlewares in the chain.

pkg/server/service/service_test.go

@@ -10,9 +10,11 @@ import (
 	"net/textproto"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	ptypes "github.com/traefik/paerser/types"
 	"github.com/traefik/traefik/v3/pkg/config/dynamic"
 	"github.com/traefik/traefik/v3/pkg/config/runtime"
 	"github.com/traefik/traefik/v3/pkg/proxy/httputil"
@@ -67,6 +69,19 @@ func TestGetLoadBalancer(t *testing.T) {
 			fwd:         &forwarderMock{},
 			expectError: false,
 		},
+		{
+			desc:        "Succeeds when passive health checker is set",
+			serviceName: "test",
+			service: &dynamic.ServersLoadBalancer{
+				Strategy: dynamic.BalancerStrategyWRR,
+				PassiveHealthCheck: &dynamic.PassiveServerHealthCheck{
+					FailureWindow:     ptypes.Duration(30 * time.Second),
+					MaxFailedAttempts: 3,
+				},
+			},
+			fwd:         &forwarderMock{},
+			expectError: false,
+		},
 	}
 
 	for _, test := range testCases {