resolver/dns: Add SetMinResolutionInterval Option (#6962)

internal/resolver/dns/dns_resolver.go

@@ -41,18 +41,24 @@ import (
 	"google.golang.org/grpc/serviceconfig"
 )
 
-// EnableSRVLookups controls whether the DNS resolver attempts to fetch gRPCLB
+var (
-// addresses from SRV records.  Must not be changed after init time.
+	// EnableSRVLookups controls whether the DNS resolver attempts to fetch gRPCLB
-var EnableSRVLookups = false
+	// addresses from SRV records.  Must not be changed after init time.
+	EnableSRVLookups = false
 
-// ResolvingTimeout specifies the maximum duration for a DNS resolution request.
+	// MinResolutionInterval is the minimum interval at which re-resolutions are
-// If the timeout expires before a response is received, the request will be canceled.
+	// allowed. This helps to prevent excessive re-resolution.
-//
+	MinResolutionInterval = 30 * time.Second
-// It is recommended to set this value at application startup. Avoid modifying this variable
-// after initialization as it's not thread-safe for concurrent modification.
-var ResolvingTimeout = 30 * time.Second
 
-var logger = grpclog.Component("dns")
+	// ResolvingTimeout specifies the maximum duration for a DNS resolution request.
+	// If the timeout expires before a response is received, the request will be canceled.
+	//
+	// It is recommended to set this value at application startup. Avoid modifying this variable
+	// after initialization as it's not thread-safe for concurrent modification.
+	ResolvingTimeout = 30 * time.Second
+
+	logger = grpclog.Component("dns")
+)
 
 func init() {
 	resolver.Register(NewBuilder())
@@ -208,7 +214,7 @@ func (d *dnsResolver) watcher() {
 			// Success resolving, wait for the next ResolveNow. However, also wait 30
 			// seconds at the very least to prevent constantly re-resolving.
 			backoffIndex = 1
-			waitTime = internal.MinResolutionRate
+			waitTime = MinResolutionInterval
 			select {
 			case <-d.ctx.Done():
 				return

internal/resolver/dns/dns_resolver_test.go

@@ -68,11 +68,11 @@ func overrideNetResolver(t *testing.T, r *testNetResolver) {
 	t.Cleanup(func() { dnsinternal.NewNetResolver = origNetResolver })
 }
 
-// Override the DNS Min Res Rate used by the resolver.
+// Override the DNS minimum resolution interval used by the resolver.
-func overrideResolutionRate(t *testing.T, d time.Duration) {
+func overrideResolutionInterval(t *testing.T, d time.Duration) {
-	origMinResRate := dnsinternal.MinResolutionRate
+	origMinResInterval := dns.MinResolutionInterval
-	dnsinternal.MinResolutionRate = d
+	dnspublic.SetMinResolutionInterval(d)
-	t.Cleanup(func() { dnsinternal.MinResolutionRate = origMinResRate })
+	t.Cleanup(func() { dnspublic.SetMinResolutionInterval(origMinResInterval) })
 }
 
 // Override the timer used by the DNS resolver to fire after a duration of d.
@@ -636,7 +636,7 @@ func (s) TestDNSResolver_ExponentialBackoff(t *testing.T) {
 func (s) TestDNSResolver_ResolveNow(t *testing.T) {
 	const target = "foo.bar.com"
 
-	overrideResolutionRate(t, 0)
+	overrideResolutionInterval(t, 0)
 	overrideTimeAfterFunc(t, 0)
 	tr := &testNetResolver{
 		hostLookupTable: map[string][]string{
@@ -739,7 +739,7 @@ func (s) TestIPResolver(t *testing.T) {
 
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
-			overrideResolutionRate(t, 0)
+			overrideResolutionInterval(t, 0)
 			overrideTimeAfterFunc(t, 2*defaultTestTimeout)
 			r, stateCh, _ := buildResolverWithTestClientConn(t, test.target)
 
@@ -1258,3 +1258,35 @@ func (s) TestResolveTimeout(t *testing.T) {
 		}
 	}
 }
+
+// Test verifies that changing [MinResolutionInterval] variable correctly effects
+// the resolution behaviour
+func (s) TestMinResolutionInterval(t *testing.T) {
+	const target = "foo.bar.com"
+
+	overrideResolutionInterval(t, 1*time.Millisecond)
+	tr := &testNetResolver{
+		hostLookupTable: map[string][]string{
+			"foo.bar.com": {"1.2.3.4", "5.6.7.8"},
+		},
+		txtLookupTable: map[string][]string{
+			"_grpc_config.foo.bar.com": txtRecordServiceConfig(txtRecordGood),
+		},
+	}
+	overrideNetResolver(t, tr)
+
+	r, stateCh, _ := buildResolverWithTestClientConn(t, target)
+
+	wantAddrs := []resolver.Address{{Addr: "1.2.3.4" + colonDefaultPort}, {Addr: "5.6.7.8" + colonDefaultPort}}
+	wantSC := scJSON
+
+	for i := 0; i < 5; i++ {
+		// set context timeout slightly higher than the min resolution interval to make sure resolutions
+		// happen successfully
+		ctx, cancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
+		defer cancel()
+
+		verifyUpdateFromResolver(ctx, t, stateCh, wantAddrs, nil, wantSC)
+		r.ResolveNow(resolver.ResolveNowOptions{})
+	}
+}

internal/resolver/dns/internal/internal.go

@@ -50,10 +50,6 @@ var (
 
 // The following vars are overridden from tests.
 var (
-	// MinResolutionRate is the minimum rate at which re-resolutions are
-	// allowed. This helps to prevent excessive re-resolution.
-	MinResolutionRate = 30 * time.Second
-
 	// TimeAfterFunc is used by the DNS resolver to wait for the given duration
 	// to elapse. In non-test code, this is implemented by time.After.  In test
 	// code, this can be used to control the amount of time the resolver is

resolver/dns/dns_resolver.go

@@ -52,3 +52,9 @@ func SetResolvingTimeout(timeout time.Duration) {
 func NewBuilder() resolver.Builder {
 	return dns.NewBuilder()
 }
+
+// SetMinResolutionInterval sets the default minimum interval at which DNS re-resolutions are
+// allowed. This helps to prevent excessive re-resolution.
+func SetMinResolutionInterval(d time.Duration) {
+	dns.MinResolutionInterval = d
+}