xdsclient: read bootstrap config before creating the first xDS client in DefaultPool (#8164)

xds/internal/xdsclient/clientimpl.go

@@ -113,19 +113,7 @@ func init() {
 	internal.TriggerXDSResourceNotFoundForTesting = triggerXDSResourceNotFoundForTesting
 	xdsclientinternal.ResourceWatchStateForTesting = resourceWatchStateForTesting
 
-	// DefaultPool is initialized with bootstrap configuration from one of the
-	// supported environment variables. If the environment variables are not
-	// set, then fallback bootstrap configuration should be set before
-	// attempting to create an xDS client, else xDS client creation will fail.
-	config, err := bootstrap.GetConfiguration()
-	if err != nil {
-		if logger.V(2) {
-			logger.Infof("Failed to read xDS bootstrap config from env vars:  %v", err)
-		}
-		DefaultPool = &Pool{clients: make(map[string]*clientRefCounted)}
-		return
-	}
-	DefaultPool = &Pool{clients: make(map[string]*clientRefCounted), config: config}
+	DefaultPool = &Pool{clients: make(map[string]*clientRefCounted)}
 }
 
 // newClientImpl returns a new xdsClient with the given config.

xds/internal/xdsclient/pool.go

@@ -220,7 +220,25 @@ func (p *Pool) newRefCounted(name string, watchExpiryTimeout time.Duration, stre
 	defer p.mu.Unlock()
 
 	if p.config == nil {
-		return nil, nil, fmt.Errorf("xds: bootstrap configuration not set in the pool")
+		if len(p.clients) != 0 || p != DefaultPool {
+			// If the current pool `p` already contains xDS clients or it is not
+			// the `DefaultPool`, the bootstrap config should have been already
+			// present in the pool.
+			return nil, nil, fmt.Errorf("xds: bootstrap configuration not set in the pool")
+		}
+		// If the current pool `p` is the `DefaultPool` and has no clients, it
+		// might be the first time an xDS client is being created on it. So,
+		// the bootstrap configuration is read from environment variables.
+		//
+		// DefaultPool is initialized with bootstrap configuration from one of the
+		// supported environment variables. If the environment variables are not
+		// set, then fallback bootstrap configuration should be set before
+		// attempting to create an xDS client, else xDS client creation will fail.
+		config, err := bootstrap.GetConfiguration()
+		if err != nil {
+			return nil, nil, fmt.Errorf("xds: failed to read xDS bootstrap config from env vars:  %v", err)
+		}
+		p.config = config
 	}
 
 	if c := p.clients[name]; c != nil {

xds/internal/xdsclient/pool/pool_test.go

@@ -0,0 +1,88 @@
+/*
+ *
+ * Copyright 2025 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package pool_test
+
+import (
+	"encoding/json"
+	"fmt"
+	"testing"
+
+	"github.com/google/uuid"
+	"google.golang.org/grpc/internal/grpctest"
+	"google.golang.org/grpc/internal/testutils"
+	"google.golang.org/grpc/internal/testutils/stats"
+	"google.golang.org/grpc/internal/xds/bootstrap"
+	"google.golang.org/grpc/xds/internal/xdsclient"
+)
+
+type s struct {
+	grpctest.Tester
+}
+
+func Test(t *testing.T) {
+	grpctest.RunSubTests(t, s{})
+}
+
+// TestDefaultPool_LazyLoadBootstrapConfig verifies that the DefaultPool
+// lazily loads the bootstrap configuration from environment variables when
+// an xDS client is created for the first time.
+//
+// If tries to create the new client in DefaultPool at the start of test when
+// none of the env vars are set. This should fail.
+//
+// Then it sets the env var XDSBootstrapFileName and retry creating a client
+// in DefaultPool. This should succeed.
+func (s) TestDefaultPool_LazyLoadBootstrapConfig(t *testing.T) {
+	_, closeFunc, err := xdsclient.DefaultPool.NewClient(t.Name(), &stats.NoopMetricsRecorder{})
+	if err == nil {
+		t.Fatalf("xdsclient.DefaultPool.NewClient() succeeded without setting bootstrap config env vars, want failure")
+	}
+
+	bs, err := bootstrap.NewContentsForTesting(bootstrap.ConfigOptionsForTesting{
+		Servers: []byte(fmt.Sprintf(`[{
+			 "server_uri": %q,
+			 "channel_creds": [{"type": "insecure"}]
+		 }]`, "non-existent-management-server")),
+		Node: []byte(fmt.Sprintf(`{"id": "%s"}`, uuid.New().String())),
+		CertificateProviders: map[string]json.RawMessage{
+			"cert-provider-instance": json.RawMessage("{}"),
+		},
+	})
+	if err != nil {
+		t.Fatalf("Failed to create bootstrap configuration: %v", err)
+	}
+
+	testutils.CreateBootstrapFileForTesting(t, bs)
+	if cfg := xdsclient.DefaultPool.BootstrapConfigForTesting(); cfg != nil {
+		t.Fatalf("DefaultPool.BootstrapConfigForTesting() = %v, want nil", cfg)
+	}
+
+	_, closeFunc, err = xdsclient.DefaultPool.NewClient(t.Name(), &stats.NoopMetricsRecorder{})
+	if err != nil {
+		t.Fatalf("Failed to create xDS client: %v", err)
+	}
+	defer func() {
+		closeFunc()
+		xdsclient.DefaultPool.UnsetBootstrapConfigForTesting()
+	}()
+
+	if xdsclient.DefaultPool.BootstrapConfigForTesting() == nil {
+		t.Fatalf("DefaultPool.BootstrapConfigForTesting() = nil, want non-nil")
+	}
+}

xds/server_test.go

@@ -178,7 +178,7 @@ func (s) TestNewServer_Failure(t *testing.T) {
 		{
 			desc:       "bootstrap env var not set",
 			serverOpts: []grpc.ServerOption{grpc.Creds(xdsCreds), BootstrapContentsForTesting(nil)},
-			wantErr:    "bootstrap configuration not set in the pool",
+			wantErr:    "failed to read xDS bootstrap config from env vars",
 		},
 		{
 			desc: "empty bootstrap config",