Implement mTLS resources and configuration for Target Allocator server

cmd/amazon-cloudwatch-agent-target-allocator/config/certwatcher.go

@@ -0,0 +1,113 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+package config
+
+import (
+	"context"
+	"crypto/tls"
+	"crypto/x509"
+	"fmt"
+	"os"
+	"sync"
+	"time"
+
+	"github.com/fsnotify/fsnotify"
+	"sigs.k8s.io/controller-runtime/pkg/certwatcher"
+)
+
+type CertAndCAWatcher struct {
+	certWatcher *certwatcher.CertWatcher
+
+	caFilePath string
+	caPool     *x509.CertPool
+	caWatcher  *fsnotify.Watcher
+
+	mu sync.RWMutex
+}
+
+func NewCertAndCAWatcher(certPath, keyPath, caPath string) (*CertAndCAWatcher, error) {
+	certWatcher, err := certwatcher.New(certPath, keyPath)
+	if err != nil {
+		return nil, fmt.Errorf("error creating cert watcher: %w", err)
+	}
+
+	caPool, err := loadCAPool(caPath)
+	if err != nil {
+		return nil, fmt.Errorf("error loading CA pool: %w", err)
+	}
+
+	caWatcher, err := fsnotify.NewWatcher()
+	if err != nil {
+		return nil, fmt.Errorf("error creating CA file watcher: %w", err)
+	}
+	if err := caWatcher.Add(caPath); err != nil {
+		return nil, fmt.Errorf("error adding CA file to watcher: %w", err)
+	}
+
+	return &CertAndCAWatcher{
+		certWatcher: certWatcher,
+		caFilePath:  caPath,
+		caPool:      caPool,
+		caWatcher:   caWatcher,
+	}, nil
+}
+
+func loadCAPool(caPath string) (*x509.CertPool, error) {
+	caCert, err := os.ReadFile(caPath)
+	caCertPool := x509.NewCertPool()
+	if err != nil {
+		return nil, fmt.Errorf("error reading CA file: %w", err)
+	}
+	caCertPool.AppendCertsFromPEM(caCert)
+	return caCertPool, nil
+}
+
+func (w *CertAndCAWatcher) Start(ctx context.Context) error {
+	go func() {
+		_ = w.certWatcher.Start(ctx)
+	}()
+
+	go w.watchCA(ctx)
+
+	<-ctx.Done()
+	return nil
+}
+
+func (w *CertAndCAWatcher) watchCA(ctx context.Context) {
+	for {
+		select {
+		case event, ok := <-w.caWatcher.Events:
+			if !ok {
+				return
+			}
+			if event.Op.Has(fsnotify.Write) || event.Op.Has(fsnotify.Create) || event.Op.Has(fsnotify.Remove) {
+				newPool, err := loadCAPool(w.caFilePath)
+				if err != nil {
+					continue
+				}
+				w.mu.Lock()
+				w.caPool = newPool
+				w.mu.Unlock()
+
+				// needed incase file removed
+				if event.Op.Has(fsnotify.Remove) {
+					time.Sleep(100 * time.Millisecond)
+					_ = w.caWatcher.Add(w.caFilePath)
+				}
+			}
+		case <-ctx.Done():
+			return
+		}
+	}
+}
+
+func (w *CertAndCAWatcher) GetCertificate(clientHello *tls.ClientHelloInfo) (*tls.Certificate, error) {
+	return w.certWatcher.GetCertificate(clientHello)
+}
+
+func (w *CertAndCAWatcher) GetCAPool() *x509.CertPool {
+	w.mu.RLock()
+	defer w.mu.RUnlock()
+	return w.caPool
+}

cmd/amazon-cloudwatch-agent-target-allocator/config/certwatcher_test.go

@@ -0,0 +1,140 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+package config
+
+import (
+	"bytes"
+	"context"
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/pem"
+	"math/big"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+func generateSelfSignedCertAndKey(commonName string) (certPEM, keyPEM []byte, err error) {
+	// Generate RSA key
+	priv, err := rsa.GenerateKey(rand.Reader, 2048)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	// Create a minimal self-signed certificate template
+	serial, err := rand.Int(rand.Reader, big.NewInt(1<<63-1))
+	if err != nil {
+		return nil, nil, err
+	}
+
+	template := &x509.Certificate{
+		SerialNumber: serial,
+		Subject: pkix.Name{
+			CommonName: commonName,
+		},
+		NotBefore: time.Now().Add(-time.Hour),
+		NotAfter:  time.Now().Add(time.Hour),
+
+		KeyUsage:              x509.KeyUsageDigitalSignature | x509.KeyUsageKeyEncipherment | x509.KeyUsageCertSign,
+		IsCA:                  true,
+		BasicConstraintsValid: true,
+	}
+
+	// Self-sign the certificate
+	der, err := x509.CreateCertificate(rand.Reader, template, template, &priv.PublicKey, priv)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	// Encode cert + key to PEM
+	var certBuf, keyBuf bytes.Buffer
+	err = pem.Encode(&certBuf, &pem.Block{Type: "CERTIFICATE", Bytes: der})
+	if err != nil {
+		return nil, nil, err
+	}
+	err = pem.Encode(&keyBuf, &pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(priv)})
+	if err != nil {
+		return nil, nil, err
+	}
+
+	return certBuf.Bytes(), keyBuf.Bytes(), nil
+}
+
+func TestCertAndCAWatcher_UpdatesCA(t *testing.T) {
+	t.Parallel()
+
+	// Generate a server cert/key for certwatcher
+	certPEM, keyPEM, err := generateSelfSignedCertAndKey("test-server")
+	if err != nil {
+		t.Fatalf("failed to generate server cert/key: %v", err)
+	}
+
+	// Generate two distinct self-signed certs to represent old CA vs new CA
+	oldCAPEM, _, err := generateSelfSignedCertAndKey("old-ca")
+	if err != nil {
+		t.Fatalf("failed to generate old CA: %v", err)
+	}
+	newCAPEM, _, err := generateSelfSignedCertAndKey("new-ca")
+	if err != nil {
+		t.Fatalf("failed to generate new CA: %v", err)
+	}
+
+	// Write all these PEM files into a temp dir
+	tmpDir := t.TempDir()
+
+	certPath := filepath.Join(tmpDir, "tls.crt")
+	keyPath := filepath.Join(tmpDir, "tls.key")
+	caPath := filepath.Join(tmpDir, "ca.crt")
+
+	if err := os.WriteFile(certPath, certPEM, 0600); err != nil {
+		t.Fatalf("failed to write cert file: %v", err)
+	}
+	if err := os.WriteFile(keyPath, keyPEM, 0600); err != nil {
+		t.Fatalf("failed to write key file: %v", err)
+	}
+	if err := os.WriteFile(caPath, oldCAPEM, 0600); err != nil {
+		t.Fatalf("failed to write initial CA file: %v", err)
+	}
+
+	// Create the CertAndCAWatcher using our files
+	watcher, err := NewCertAndCAWatcher(certPath, keyPath, caPath)
+	if err != nil {
+		t.Fatalf("failed to create CertAndCAWatcher: %v", err)
+	}
+
+	// Start the watcher in the background
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	go func() {
+		_ = watcher.Start(ctx)
+	}()
+
+	// Record the initial CA pool pointer
+	oldPool := watcher.GetCAPool()
+	if oldPool == nil {
+		t.Fatal("expected non-nil initial CA pool")
+	}
+
+	// Overwrite the CA file with newCAPEM, triggering a reload
+	if err := os.WriteFile(caPath, newCAPEM, 0600); err != nil {
+		t.Fatalf("failed to write new CA file: %v", err)
+	}
+
+	// Loop until the watcher updates the CA pool (or times out)
+	deadline := time.Now().Add(2 * time.Second)
+	for {
+		newPool := watcher.GetCAPool()
+		if newPool != oldPool {
+			t.Log("CA pool successfully updated.")
+			return
+		}
+		if time.Now().After(deadline) {
+			t.Fatal("timed out waiting for CA pool to be updated")
+		}
+		time.Sleep(100 * time.Millisecond)
+	}
+}

cmd/amazon-cloudwatch-agent-target-allocator/config/config.go

@@ -6,7 +6,6 @@ package config
 import (
 	"context"
 	"crypto/tls"
-	"crypto/x509"
 	"errors"
 	"fmt"
 	"io/fs"
@@ -24,23 +23,22 @@ import (
 	"k8s.io/client-go/tools/clientcmd"
 	"k8s.io/klog/v2"
 	ctrl "sigs.k8s.io/controller-runtime"
-	"sigs.k8s.io/controller-runtime/pkg/certwatcher"
 	"sigs.k8s.io/controller-runtime/pkg/log/zap"
 
 	tamanifest "github.com/aws/amazon-cloudwatch-agent-operator/internal/manifests/targetallocator"
 )
 
 const (
-	DefaultResyncTime                        = 5 * time.Minute
-	DefaultConfigFilePath     string         = "/conf/targetallocator.yaml"
-	DefaultCRScrapeInterval   model.Duration = model.Duration(time.Second * 30)
-	DefaultAllocationStrategy                = "consistent-hashing"
-	DefaultFilterStrategy                    = "relabel-config"
-	DefaultListenAddr                        = ":8443"
-	DefaultCertMountPath                     = tamanifest.TACertMountPath
-	DefaultTLSKeyPath                        = DefaultCertMountPath + "/server.key"
-	DefaultTLSCertPath                       = DefaultCertMountPath + "/server.crt"
-	DefaultCABundlePath                      = ""
+	DefaultResyncTime                         = 5 * time.Minute
+	DefaultConfigFilePath      string         = "/conf/targetallocator.yaml"
+	DefaultCRScrapeInterval    model.Duration = model.Duration(time.Second * 30)
+	DefaultAllocationStrategy                 = "consistent-hashing"
+	DefaultListenAddr                         = ":8443"
+	DefaultCertMountPath                      = tamanifest.TACertMountPath
+	DefaultClientCertMountPath                = tamanifest.ClientCertMountPath
+	DefaultTLSKeyPath                         = DefaultCertMountPath + "/server.key"
+	DefaultTLSCertPath                        = DefaultCertMountPath + "/server.crt"
+	DefaultCABundlePath                       = DefaultClientCertMountPath + "/tls-ca.crt"
 )
 
 type Config struct {
@@ -150,7 +148,6 @@ func LoadFromCLI(target *Config, flagSet *pflag.FlagSet) error {
 }
 
 func unmarshal(cfg *Config, configFile string) error {
-
 	yamlFile, err := os.ReadFile(configFile)
 	if err != nil {
 		return err
@@ -217,31 +214,29 @@ func ValidateConfig(config *Config) error {
 }
 
 func (c HTTPSServerConfig) NewTLSConfig(ctx context.Context) (*tls.Config, error) {
-	tlsConfig := &tls.Config{
-		MinVersion: tls.VersionTLS13,
-	}
-
-	certWatcher, err := certwatcher.New(c.TLSCertFilePath, c.TLSKeyFilePath)
+	certWatcher, err := NewCertAndCAWatcher(c.TLSCertFilePath, c.TLSKeyFilePath, c.CAFilePath)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("error creating certwatcher: %w", err)
 	}
-	tlsConfig.GetCertificate = certWatcher.GetCertificate
+
 	go func() {
 		_ = certWatcher.Start(ctx)
 	}()
 
-	if c.CAFilePath == "" {
-		return tlsConfig, nil
+	// Create the TLS config
+	tlsConfig := &tls.Config{
+		MinVersion:     tls.VersionTLS13,
+		GetCertificate: certWatcher.GetCertificate,
+		ClientCAs:      certWatcher.GetCAPool(),
+		ClientAuth:     tls.RequireAndVerifyClientCert,
 	}
 
-	caCert, err := os.ReadFile(c.CAFilePath)
-	caCertPool := x509.NewCertPool()
-	if err != nil {
-		return nil, err
+	// Dynamically update the CA pool if needed
+	tlsConfig.GetConfigForClient = func(clientHello *tls.ClientHelloInfo) (*tls.Config, error) {
+		newTLSConfig := tlsConfig.Clone()
+		newTLSConfig.ClientCAs = certWatcher.GetCAPool()
+		return newTLSConfig, nil
 	}
-	caCertPool.AppendCertsFromPEM(caCert)
-	tlsConfig.ClientCAs = caCertPool
-	tlsConfig.ClientAuth = tls.RequireAndVerifyClientCert
 
 	return tlsConfig, nil
 }