feat(shard-distributor): integrate dynamic config for spectator (#7722)

**What changed?**
Integrated dynamic config check for spectator enablement and exported
ModeKey constants in membership package

**Why?**
The spectator client needs to respond to dynamic config changes for
MatchingShardDistributionMode. Previously, ModeKey constants were
private in the membership package, preventing external packages from
checking the current mode. This change exports the ModeKey type and
constants, and adds an Enabled function to spectator params that
dynamically checks if the mode is not hash_ring. This allows the
spectator to automatically enable/disable based on the dynamic config
without requiring restarts.

**How did you test it?**
- Unit tests: `go test -v ./common/membership -run
TestShardDistributorResolver`
- All tests pass with the exported constants

**Potential risks**
- API change: Exported previously private ModeKey type and constants
(ModeKeyHashRing, ModeKeyShardDistributor,
ModeKeyHashRingShadowShardDistributor,
ModeKeyShardDistributorShadowHashRing). This is backwards compatible as
it only adds public visibility without breaking existing code.
- Behavior change: Spectator now dynamically responds to config changes
rather than using a static configuration

**Release notes**
N/A - internal improvement to spectator configuration handling

**Documentation Changes**
N/A

---------

Signed-off-by: Jakob Haahr Taankvist <jht@uber.com>

Author: jakobht

cmd/server/cadence/server.go

@@ -179,12 +179,17 @@ func (s *server) startService() common.Daemon {
 		if len(s.cfg.ShardDistributorMatchingConfig.Namespaces) > 1 {
 			s.logger.Fatal("spectator does not support multiple namespaces", tag.Value(s.cfg.ShardDistributorMatchingConfig.Namespaces))
 		}
+		matchingShardDistributionMode := dc.GetStringProperty(dynamicproperties.MatchingShardDistributionMode)
+
 		spectatorParams := spectatorclient.Params{
 			Client:       shardDistributorClient,
 			MetricsScope: params.MetricScope,
 			Logger:       params.Logger,
 			Config:       s.cfg.ShardDistributorMatchingConfig,
 			TimeSource:   clock.NewRealTimeSource(),
+			Enabled: func() bool {
+				return membership.ModeKey(matchingShardDistributionMode()) != membership.ModeKeyHashRing
+			},
 		}
 		namespace := s.cfg.ShardDistributorMatchingConfig.Namespaces[0].Namespace
 		spectator, err = spectatorclient.NewSpectatorWithNamespace(

common/membership/sharddistributorresolver.go

@@ -35,13 +35,17 @@ import (
 	"github.com/uber/cadence/service/sharddistributor/client/spectatorclient"
 )
 
-type modeKey string
-
-var (
-	modeKeyHashRing                       modeKey = "hash_ring"
-	modeKeyShardDistributor               modeKey = "shard_distributor"
-	modeKeyHashRingShadowShardDistributor modeKey = "hash_ring-shadow-shard_distributor"
-	modeKeyShardDistributorShadowHashRing modeKey = "shard_distributor-shadow-hash_ring"
+type ModeKey string
+
+const (
+	// ModeKeyHashRing represents the hash ring shard distribution mode
+	ModeKeyHashRing ModeKey = "hash_ring"
+	// ModeKeyShardDistributor represents the shard distributor mode
+	ModeKeyShardDistributor ModeKey = "shard_distributor"
+	// ModeKeyHashRingShadowShardDistributor represents hash ring mode with shard distributor shadow
+	ModeKeyHashRingShadowShardDistributor ModeKey = "hash_ring-shadow-shard_distributor"
+	// ModeKeyShardDistributorShadowHashRing represents shard distributor mode with hash ring shadow
+	ModeKeyShardDistributorShadowHashRing ModeKey = "shard_distributor-shadow-hash_ring"
 )
 
 type shardDistributorResolver struct {
@@ -87,12 +91,12 @@ func (s shardDistributorResolver) Lookup(key string) (HostInfo, error) {
 		return s.ring.Lookup(key)
 	}
 
-	switch modeKey(s.shardDistributionMode()) {
-	case modeKeyHashRing:
+	switch ModeKey(s.shardDistributionMode()) {
+	case ModeKeyHashRing:
 		return s.ring.Lookup(key)
-	case modeKeyShardDistributor:
+	case ModeKeyShardDistributor:
 		return s.lookUpInShardDistributor(key)
-	case modeKeyHashRingShadowShardDistributor:
+	case ModeKeyHashRingShadowShardDistributor:
 		hashRingResult, err := s.ring.Lookup(key)
 		if err != nil {
 			return HostInfo{}, err
@@ -108,7 +112,7 @@ func (s shardDistributorResolver) Lookup(key string) (HostInfo, error) {
 		}()
 
 		return hashRingResult, nil
-	case modeKeyShardDistributorShadowHashRing:
+	case ModeKeyShardDistributorShadowHashRing:
 		shardDistributorResult, err := s.lookUpInShardDistributor(key)
 		if err != nil {
 			return HostInfo{}, err

common/membership/sharddistributorresolver_test.go

@@ -38,7 +38,7 @@ import (
 func TestShardDistributorResolver_Lookup_modeHashRing(t *testing.T) {
 	resolver, ring, _ := newShardDistributorResolver(t)
 	resolver.shardDistributionMode = func(...dynamicproperties.FilterOption) string {
-		return string(modeKeyHashRing)
+		return string(ModeKeyHashRing)
 	}
 
 	ring.EXPECT().Lookup("test-key").Return(HostInfo{addr: "test-addr"}, nil)
@@ -51,7 +51,7 @@ func TestShardDistributorResolver_Lookup_modeHashRing(t *testing.T) {
 func TestShardDistributorResolver_Lookup_modeShardDistributor(t *testing.T) {
 	resolver, _, shardDistributorMock := newShardDistributorResolver(t)
 	resolver.shardDistributionMode = func(...dynamicproperties.FilterOption) string {
-		return string(modeKeyShardDistributor)
+		return string(ModeKeyShardDistributor)
 	}
 
 	shardDistributorMock.EXPECT().GetShardOwner(gomock.Any(), "test-key").
@@ -72,7 +72,7 @@ func TestShardDistributorResolver_Lookup_modeShardDistributor(t *testing.T) {
 func TestShardDistributorResolver_Lookup_modeHashRingShadowShardDistributor(t *testing.T) {
 	resolver, ring, shardDistributorMock := newShardDistributorResolver(t)
 	resolver.shardDistributionMode = func(...dynamicproperties.FilterOption) string {
-		return string(modeKeyHashRingShadowShardDistributor)
+		return string(ModeKeyHashRingShadowShardDistributor)
 	}
 
 	cases := []struct {
@@ -158,7 +158,7 @@ func TestShardDistributorResolver_Lookup_modeHashRingShadowShardDistributor(t *t
 func TestShardDistributorResolver_Lookup_modeShardDistributorShadowHashRing(t *testing.T) {
 	resolver, ring, shardDistributorMock := newShardDistributorResolver(t)
 	resolver.shardDistributionMode = func(...dynamicproperties.FilterOption) string {
-		return string(modeKeyShardDistributorShadowHashRing)
+		return string(ModeKeyShardDistributorShadowHashRing)
 	}
 
 	cases := []struct {