updated admission-controller to have adjustable --min-tls-version and…

… --tls-ciphers

vertical-pod-autoscaler/pkg/admission-controller/README.md

@@ -32,6 +32,8 @@ up the changes: ```sudo systemctl restart kubelet.service```
    for pods on their creation & updates.
 1. You can specify a path for it to register as a part of the installation process
    by setting `--register-by-url=true` and passing `--webhook-address` and `--webhook-port`.
+1. You can specify a minimum TLS version with `--min-tls-version` with acceptable values being `tls1_2` (default), or `tls1_3`.
+1. You can also specify a comma or colon separated list of ciphers for the server to use with `--tls-ciphers` if `--min-tls-version` is set to `tls1_2`.
 
 ## Implementation
 

vertical-pod-autoscaler/pkg/admission-controller/config.go

@@ -19,6 +19,8 @@ package main
 import (
 	"context"
 	"crypto/tls"
+	"fmt"
+	"strings"
 	"time"
 
 	admissionregistration "k8s.io/api/admissionregistration/v1"
@@ -31,14 +33,43 @@ const (
 	webhookConfigName = "vpa-webhook-config"
 )
 
-func configTLS(serverCert, serverKey []byte) *tls.Config {
+func configTLS(serverCert, serverKey []byte, minTlsVersion, ciphers string) *tls.Config {
+	var tlsVersion uint16
+	var ciphersuites []uint16
+	reverseCipherMap := make(map[string]uint16)
 	sCert, err := tls.X509KeyPair(serverCert, serverKey)
 	if err != nil {
 		klog.Fatal(err)
 	}
+
+	for _, c := range tls.CipherSuites() {
+		reverseCipherMap[c.Name] = c.ID
+	}
+	for _, c := range strings.Split(strings.ReplaceAll(ciphers, ",", ":"), ":") {
+		cipher, ok := reverseCipherMap[c]
+		if ok {
+			ciphersuites = append(ciphersuites, cipher)
+		}
+	}
+	if len(ciphersuites) == 0 {
+		ciphersuites = nil
+	}
+
+	switch minTlsVersion {
+	case "":
+		fallthrough
+	case "tls1_2":
+		tlsVersion = tls.VersionTLS12
+	case "tls1_3":
+		tlsVersion = tls.VersionTLS13
+	default:
+		klog.Fatal(fmt.Errorf("Unable to determine value for --min-tls-version (%s), must be either tls1_2 or tls1_3", minTlsVersion))
+	}
+
 	return &tls.Config{
-		MinVersion:   tls.VersionTLS12,
+		MinVersion:   tlsVersion,
 		Certificates: []tls.Certificate{sCert},
+		CipherSuites: ciphersuites,
 	}
 }
 

vertical-pod-autoscaler/pkg/admission-controller/main.go

@@ -59,6 +59,8 @@ var (
 		tlsCertFile:   flag.String("tls-cert-file", "/etc/tls-certs/serverCert.pem", "Path to server certificate PEM file."),
 		tlsPrivateKey: flag.String("tls-private-key", "/etc/tls-certs/serverKey.pem", "Path to server certificate key PEM file."),
 	}
+	ciphers       = flag.String("tls-ciphers", "", "A comma-separated or colon-separated list of ciphers to accept.  Only works when min-tls-version is set to tls1_2.")
+	minTlsVersion = flag.String("min-tls-version", "tls1_2", "The minimum TLS version to accept.  Must be set to either tls1_2 (default) or tls1_3.")
 
 	port               = flag.Int("port", 8000, "The port to listen on.")
 	address            = flag.String("address", ":8944", "The address to expose Prometheus metrics.")
@@ -131,7 +133,7 @@ func main() {
 	})
 	server := &http.Server{
 		Addr:      fmt.Sprintf(":%d", *port),
-		TLSConfig: configTLS(certs.serverCert, certs.serverKey),
+		TLSConfig: configTLS(certs.serverCert, certs.serverKey, *minTlsVersion, *ciphers),
 	}
 	url := fmt.Sprintf("%v:%v", *webhookAddress, *webhookPort)
 	go func() {