Update dependencies to v0.27.4 tag

Automated cherry pick of #117791: update serial number to a valid non-zero number in ca

Kubernetes-commit: db247e1df34efd17a55a513f196bf53224489a49

discovery/discovery_client.go

@@ -20,6 +20,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"mime"
 	"net/http"
 	"net/url"
 	"sort"
@@ -58,8 +59,9 @@ const (
 	defaultBurst = 300
 
 	AcceptV1 = runtime.ContentTypeJSON
-	// Aggregated discovery content-type (currently v2beta1). NOTE: Currently, we are assuming the order
-	// for "g", "v", and "as" from the server. We can only compare this string if we can make that assumption.
+	// Aggregated discovery content-type (v2beta1). NOTE: content-type parameters
+	// MUST be ordered (g, v, as) for server in "Accept" header (BUT we are resilient
+	// to ordering when comparing returned values in "Content-Type" header).
 	AcceptV2Beta1 = runtime.ContentTypeJSON + ";" + "g=apidiscovery.k8s.io;v=v2beta1;as=APIGroupDiscoveryList"
 	// Prioritize aggregated discovery by placing first in the order of discovery accept types.
 	acceptDiscoveryFormats = AcceptV2Beta1 + "," + AcceptV1
@@ -259,8 +261,16 @@ func (d *DiscoveryClient) downloadLegacy() (
 
 	var resourcesByGV map[schema.GroupVersion]*metav1.APIResourceList
 	// Switch on content-type server responded with: aggregated or unaggregated.
-	switch responseContentType {
-	case AcceptV1:
+	switch {
+	case isV2Beta1ContentType(responseContentType):
+		var aggregatedDiscovery apidiscovery.APIGroupDiscoveryList
+		err = json.Unmarshal(body, &aggregatedDiscovery)
+		if err != nil {
+			return nil, nil, nil, err
+		}
+		apiGroupList, resourcesByGV, failedGVs = SplitGroupsAndResources(aggregatedDiscovery)
+	default:
+		// Default is unaggregated discovery v1.
 		var v metav1.APIVersions
 		err = json.Unmarshal(body, &v)
 		if err != nil {
@@ -271,15 +281,6 @@ func (d *DiscoveryClient) downloadLegacy() (
 			apiGroup = apiVersionsToAPIGroup(&v)
 		}
 		apiGroupList.Groups = []metav1.APIGroup{apiGroup}
-	case AcceptV2Beta1:
-		var aggregatedDiscovery apidiscovery.APIGroupDiscoveryList
-		err = json.Unmarshal(body, &aggregatedDiscovery)
-		if err != nil {
-			return nil, nil, nil, err
-		}
-		apiGroupList, resourcesByGV, failedGVs = SplitGroupsAndResources(aggregatedDiscovery)
-	default:
-		return nil, nil, nil, fmt.Errorf("Unknown discovery response content-type: %s", responseContentType)
 	}
 
 	return apiGroupList, resourcesByGV, failedGVs, nil
@@ -313,13 +314,8 @@ func (d *DiscoveryClient) downloadAPIs() (
 	failedGVs := map[schema.GroupVersion]error{}
 	var resourcesByGV map[schema.GroupVersion]*metav1.APIResourceList
 	// Switch on content-type server responded with: aggregated or unaggregated.
-	switch responseContentType {
-	case AcceptV1:
-		err = json.Unmarshal(body, apiGroupList)
-		if err != nil {
-			return nil, nil, nil, err
-		}
-	case AcceptV2Beta1:
+	switch {
+	case isV2Beta1ContentType(responseContentType):
 		var aggregatedDiscovery apidiscovery.APIGroupDiscoveryList
 		err = json.Unmarshal(body, &aggregatedDiscovery)
 		if err != nil {
@@ -327,12 +323,38 @@ func (d *DiscoveryClient) downloadAPIs() (
 		}
 		apiGroupList, resourcesByGV, failedGVs = SplitGroupsAndResources(aggregatedDiscovery)
 	default:
-		return nil, nil, nil, fmt.Errorf("Unknown discovery response content-type: %s", responseContentType)
+		// Default is unaggregated discovery v1.
+		err = json.Unmarshal(body, apiGroupList)
+		if err != nil {
+			return nil, nil, nil, err
+		}
 	}
 
 	return apiGroupList, resourcesByGV, failedGVs, nil
 }
 
+// isV2Beta1ContentType checks of the content-type string is both
+// "application/json" and contains the v2beta1 content-type params.
+// NOTE: This function is resilient to the ordering of the
+// content-type parameters, as well as parameters added by
+// intermediaries such as proxies or gateways. Examples:
+//
+//	"application/json; g=apidiscovery.k8s.io;v=v2beta1;as=APIGroupDiscoveryList" = true
+//	"application/json; as=APIGroupDiscoveryList;v=v2beta1;g=apidiscovery.k8s.io" = true
+//	"application/json; as=APIGroupDiscoveryList;v=v2beta1;g=apidiscovery.k8s.io;charset=utf-8" = true
+//	"application/json" = false
+//	"application/json; charset=UTF-8" = false
+func isV2Beta1ContentType(contentType string) bool {
+	base, params, err := mime.ParseMediaType(contentType)
+	if err != nil {
+		return false
+	}
+	return runtime.ContentTypeJSON == base &&
+		params["g"] == "apidiscovery.k8s.io" &&
+		params["v"] == "v2beta1" &&
+		params["as"] == "APIGroupDiscoveryList"
+}
+
 // ServerGroups returns the supported groups, with information like supported versions and the
 // preferred version.
 func (d *DiscoveryClient) ServerGroups() (*metav1.APIGroupList, error) {

discovery/discovery_client_test.go

@@ -1395,8 +1395,9 @@ func TestAggregatedServerGroups(t *testing.T) {
 			}
 			output, err := json.Marshal(agg)
 			require.NoError(t, err)
-			// Content-type is "aggregated" discovery format.
-			w.Header().Set("Content-Type", AcceptV2Beta1)
+			// Content-Type is "aggregated" discovery format. Add extra parameter
+			// to ensure we are resilient to these extra parameters.
+			w.Header().Set("Content-Type", AcceptV2Beta1+"; charset=utf-8")
 			w.WriteHeader(http.StatusOK)
 			w.Write(output)
 		}))
@@ -1985,8 +1986,9 @@ func TestAggregatedServerGroupsAndResources(t *testing.T) {
 			}
 			output, err := json.Marshal(agg)
 			require.NoError(t, err)
-			// Content-type is "aggregated" discovery format.
-			w.Header().Set("Content-Type", AcceptV2Beta1)
+			// Content-type is "aggregated" discovery format. Add extra parameter
+			// to ensure we are resilient to these extra parameters.
+			w.Header().Set("Content-Type", AcceptV2Beta1+"; charset=utf-8")
 			w.WriteHeader(http.StatusOK)
 			w.Write(output)
 		}))
@@ -2125,8 +2127,9 @@ func TestAggregatedServerGroupsAndResourcesWithErrors(t *testing.T) {
 			}
 			output, err := json.Marshal(agg)
 			require.NoError(t, err)
-			// Content-type is "aggregated" discovery format.
-			w.Header().Set("Content-Type", AcceptV2Beta1)
+			// Content-type is "aggregated" discovery format. Add extra parameter
+			// to ensure we are resilient to these extra parameters.
+			w.Header().Set("Content-Type", AcceptV2Beta1+"; charset=utf-8")
 			w.WriteHeader(status)
 			w.Write(output)
 		}))
@@ -2733,8 +2736,9 @@ func TestAggregatedServerPreferredResources(t *testing.T) {
 			}
 			output, err := json.Marshal(agg)
 			require.NoError(t, err)
-			// Content-type is "aggregated" discovery format.
-			w.Header().Set("Content-Type", AcceptV2Beta1)
+			// Content-type is "aggregated" discovery format. Add extra parameter
+			// to ensure we are resilient to these extra parameters.
+			w.Header().Set("Content-Type", AcceptV2Beta1+"; charset=utf-8")
 			w.WriteHeader(http.StatusOK)
 			w.Write(output)
 		}))
@@ -2758,6 +2762,58 @@ func TestAggregatedServerPreferredResources(t *testing.T) {
 	}
 }
 
+func TestDiscoveryContentTypeVersion(t *testing.T) {
+	tests := []struct {
+		contentType string
+		isV2Beta1   bool
+	}{
+		{
+			contentType: "application/json; g=apidiscovery.k8s.io;v=v2beta1;as=APIGroupDiscoveryList",
+			isV2Beta1:   true,
+		},
+		{
+			// content-type parameters are not in correct order, but comparison ignores order.
+			contentType: "application/json; v=v2beta1;as=APIGroupDiscoveryList;g=apidiscovery.k8s.io",
+			isV2Beta1:   true,
+		},
+		{
+			// content-type parameters are not in correct order, but comparison ignores order.
+			contentType: "application/json; as=APIGroupDiscoveryList;g=apidiscovery.k8s.io;v=v2beta1",
+			isV2Beta1:   true,
+		},
+		{
+			// Ignores extra parameter "charset=utf-8"
+			contentType: "application/json; g=apidiscovery.k8s.io;v=v2beta1;as=APIGroupDiscoveryList;charset=utf-8",
+			isV2Beta1:   true,
+		},
+		{
+			contentType: "application/json",
+			isV2Beta1:   false,
+		},
+		{
+			contentType: "application/json; charset=UTF-8",
+			isV2Beta1:   false,
+		},
+		{
+			contentType: "text/json",
+			isV2Beta1:   false,
+		},
+		{
+			contentType: "text/html",
+			isV2Beta1:   false,
+		},
+		{
+			contentType: "",
+			isV2Beta1:   false,
+		},
+	}
+
+	for _, test := range tests {
+		isV2Beta1 := isV2Beta1ContentType(test.contentType)
+		assert.Equal(t, test.isV2Beta1, isV2Beta1)
+	}
+}
+
 func TestUseLegacyDiscovery(t *testing.T) {
 	// Default client sends aggregated discovery accept format (first) as well as legacy format.
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {

go.mod

@@ -24,10 +24,10 @@ require (
 	golang.org/x/term v0.6.0
 	golang.org/x/time v0.0.0-20220210224613-90d013bbcef8
 	google.golang.org/protobuf v1.28.1
-	k8s.io/api v0.0.0
-	k8s.io/apimachinery v0.0.0
+	k8s.io/api v0.27.4
+	k8s.io/apimachinery v0.27.4
 	k8s.io/klog/v2 v2.90.1
-	k8s.io/kube-openapi v0.0.0-20230308215209-15aac26d736a
+	k8s.io/kube-openapi v0.0.0-20230501164219-8b0f38b5fd1f
 	k8s.io/utils v0.0.0-20230209194617-a36077c30491
 	sigs.k8s.io/json v0.0.0-20221116044647-bc3834ca7abd
 	sigs.k8s.io/structured-merge-diff/v4 v4.2.3
@@ -59,7 +59,6 @@ require (
 )
 
 replace (
-	k8s.io/api => ../api
-	k8s.io/apimachinery => ../apimachinery
-	k8s.io/client-go => ../client-go
+	k8s.io/api => k8s.io/api v0.27.4
+	k8s.io/apimachinery => k8s.io/apimachinery v0.27.4
 )

go.sum

@@ -177,7 +177,7 @@ github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZb
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/prometheus/client_model v0.0.0-20190812154241-14fe0d1b01d4/go.mod h1:xMI15A0UPsDsEKsMN9yxemIoYk6Tm2C1GtYGdfGttqA=
 github.com/rogpeppe/go-internal v1.3.0/go.mod h1:M8bDsm7K2OlrFYOpmOWEs/qY81heoFRclV5y23lUDJ4=
-github.com/rogpeppe/go-internal v1.10.0 h1:TMyTOH3F/DB16zRVcYyreMH6GnZZrwQVAoYjRBZyWFQ=
+github.com/rogpeppe/go-internal v1.11.0 h1:cWPaGQEPrBb5/AsnsZesgZZ9yb1OQ+GOISoDNXVBh4M=
 github.com/spf13/pflag v1.0.5 h1:iy+VFUOCP1a+8yFto/drg2CJ5u0yRoB7fZw3DKv/JXA=
 github.com/spf13/pflag v1.0.5/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
 github.com/stoewer/go-strcase v1.2.0/go.mod h1:IBiWB2sKIp3wVVQ3Y035++gc+knqhUQag1KpM8ahLw8=
@@ -477,10 +477,14 @@ honnef.co/go/tools v0.0.0-20190523083050-ea95bdfd59fc/go.mod h1:rf3lG4BRIbNafJWh
 honnef.co/go/tools v0.0.1-2019.2.3/go.mod h1:a3bituU0lyd329TUQxRnasdCoJDkEUEAqEt0JzvZhAg=
 honnef.co/go/tools v0.0.1-2020.1.3/go.mod h1:X/FiERA/W4tHapMX5mGpAtMSVEeEUOyHaw9vFzvIQ3k=
 honnef.co/go/tools v0.0.1-2020.1.4/go.mod h1:X/FiERA/W4tHapMX5mGpAtMSVEeEUOyHaw9vFzvIQ3k=
+k8s.io/api v0.27.4 h1:0pCo/AN9hONazBKlNUdhQymmnfLRbSZjd5H5H3f0bSs=
+k8s.io/api v0.27.4/go.mod h1:O3smaaX15NfxjzILfiln1D8Z3+gEYpjEpiNA/1EVK1Y=
+k8s.io/apimachinery v0.27.4 h1:CdxflD4AF61yewuid0fLl6bM4a3q04jWel0IlP+aYjs=
+k8s.io/apimachinery v0.27.4/go.mod h1:XNfZ6xklnMCOGGFNqXG7bUrQCoR04dh/E7FprV6pb+E=
 k8s.io/klog/v2 v2.90.1 h1:m4bYOKall2MmOiRaR1J+We67Do7vm9KiQVlT96lnHUw=
 k8s.io/klog/v2 v2.90.1/go.mod h1:y1WjHnz7Dj687irZUWR/WLkLc5N1YHtjLdmgWjndZn0=
-k8s.io/kube-openapi v0.0.0-20230308215209-15aac26d736a h1:gmovKNur38vgoWfGtP5QOGNOA7ki4n6qNYoFAgMlNvg=
-k8s.io/kube-openapi v0.0.0-20230308215209-15aac26d736a/go.mod h1:y5VtZWM9sHHc2ZodIH/6SHzXj+TPU5USoA8lcIeKEKY=
+k8s.io/kube-openapi v0.0.0-20230501164219-8b0f38b5fd1f h1:2kWPakN3i/k81b0gvD5C5FJ2kxm1WrQFanWchyKuqGg=
+k8s.io/kube-openapi v0.0.0-20230501164219-8b0f38b5fd1f/go.mod h1:byini6yhqGC14c3ebc/QwanvYwhuMWF6yz2F8uwW8eg=
 k8s.io/utils v0.0.0-20230209194617-a36077c30491 h1:r0BAOLElQnnFhE/ApUsg3iHdVYYPBjNSSOMowRZxxsY=
 k8s.io/utils v0.0.0-20230209194617-a36077c30491/go.mod h1:OLgZIPagt7ERELqWJFomSt595RzquPNLL48iOWgYOg0=
 rsc.io/binaryregexp v0.2.0/go.mod h1:qTv7/COck+e2FymRvadv62gMdZztPaShugOCi3I+8D8=

openapi/client.go

@@ -19,6 +19,7 @@ package openapi
 import (
 	"context"
 	"encoding/json"
+	"strings"
 
 	"k8s.io/client-go/rest"
 	"k8s.io/kube-openapi/pkg/handler3"
@@ -58,7 +59,11 @@ func (c *client) Paths() (map[string]GroupVersion, error) {
 	// Create GroupVersions for each element of the result
 	result := map[string]GroupVersion{}
 	for k, v := range discoMap.Paths {
-		result[k] = newGroupVersion(c, v)
+		// If the server returned a URL rooted at /openapi/v3, preserve any additional client-side prefix.
+		// If the server returned a URL not rooted at /openapi/v3, treat it as an actual server-relative URL.
+		// See https://github.com/kubernetes/kubernetes/issues/117463 for details
+		useClientPrefix := strings.HasPrefix(v.ServerRelativeURL, "/openapi/v3")
+		result[k] = newGroupVersion(c, v, useClientPrefix)
 	}
 	return result, nil
 }

openapi/groupversion.go

@@ -18,6 +18,7 @@ package openapi
 
 import (
 	"context"
+	"net/url"
 
 	"k8s.io/kube-openapi/pkg/handler3"
 )
@@ -29,18 +30,41 @@ type GroupVersion interface {
 }
 
 type groupversion struct {
-	client *client
-	item   handler3.OpenAPIV3DiscoveryGroupVersion
+	client          *client
+	item            handler3.OpenAPIV3DiscoveryGroupVersion
+	useClientPrefix bool
 }
 
-func newGroupVersion(client *client, item handler3.OpenAPIV3DiscoveryGroupVersion) *groupversion {
-	return &groupversion{client: client, item: item}
+func newGroupVersion(client *client, item handler3.OpenAPIV3DiscoveryGroupVersion, useClientPrefix bool) *groupversion {
+	return &groupversion{client: client, item: item, useClientPrefix: useClientPrefix}
 }
 
 func (g *groupversion) Schema(contentType string) ([]byte, error) {
-	return g.client.restClient.Get().
-		RequestURI(g.item.ServerRelativeURL).
-		SetHeader("Accept", contentType).
-		Do(context.TODO()).
-		Raw()
+	if !g.useClientPrefix {
+		return g.client.restClient.Get().
+			RequestURI(g.item.ServerRelativeURL).
+			SetHeader("Accept", contentType).
+			Do(context.TODO()).
+			Raw()
+	}
+
+	locator, err := url.Parse(g.item.ServerRelativeURL)
+	if err != nil {
+		return nil, err
+	}
+
+	path := g.client.restClient.Get().
+		AbsPath(locator.Path).
+		SetHeader("Accept", contentType)
+
+	// Other than root endpoints(openapiv3/apis), resources have hash query parameter to support etags.
+	// However, absPath does not support handling query parameters internally,
+	// so that hash query parameter is added manually
+	for k, value := range locator.Query() {
+		for _, v := range value {
+			path.Param(k, v)
+		}
+	}
+
+	return path.Do(context.TODO()).Raw()
 }

openapi/groupversion_test.go

@@ -0,0 +1,106 @@
+/*
+Copyright 2023 The Kubernetes 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 openapi
+
+import (
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	appsv1 "k8s.io/api/apps/v1"
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/client-go/kubernetes/scheme"
+	"k8s.io/client-go/rest"
+)
+
+func TestGroupVersion(t *testing.T) {
+	tests := []struct {
+		name                string
+		prefix              string
+		serverReturnsPrefix bool
+	}{
+		{
+			name:                "no prefix",
+			prefix:              "",
+			serverReturnsPrefix: false,
+		},
+		{
+			name:                "prefix not in discovery",
+			prefix:              "/test-endpoint",
+			serverReturnsPrefix: false,
+		},
+		{
+			name:                "prefix in discovery",
+			prefix:              "/test-endpoint",
+			serverReturnsPrefix: true,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				switch {
+				case r.URL.Path == test.prefix+"/openapi/v3/apis/apps/v1" && r.URL.RawQuery == "hash=014fbff9a07c":
+					w.Header().Set("Content-Type", "application/json")
+					w.WriteHeader(http.StatusOK)
+					w.Write([]byte(`{"openapi":"3.0.0","info":{"title":"Kubernetes","version":"unversioned"}}`))
+				case r.URL.Path == test.prefix+"/openapi/v3":
+					// return root content
+					w.Header().Set("Content-Type", "application/json")
+					w.WriteHeader(http.StatusOK)
+					if test.serverReturnsPrefix {
+						w.Write([]byte(fmt.Sprintf(`{"paths":{"apis/apps/v1":{"serverRelativeURL":"%s/openapi/v3/apis/apps/v1?hash=014fbff9a07c"}}}`, test.prefix)))
+					} else {
+						w.Write([]byte(`{"paths":{"apis/apps/v1":{"serverRelativeURL":"/openapi/v3/apis/apps/v1?hash=014fbff9a07c"}}}`))
+					}
+				default:
+					t.Errorf("unexpected request: %s", r.URL.String())
+					w.WriteHeader(http.StatusNotFound)
+					return
+				}
+			}))
+			defer server.Close()
+
+			c, err := rest.RESTClientFor(&rest.Config{
+				Host: server.URL + test.prefix,
+				ContentConfig: rest.ContentConfig{
+					NegotiatedSerializer: scheme.Codecs,
+					GroupVersion:         &appsv1.SchemeGroupVersion,
+				},
+			})
+
+			if err != nil {
+				t.Fatalf("unexpected error occurred: %v", err)
+			}
+
+			openapiClient := NewClient(c)
+			paths, err := openapiClient.Paths()
+			if err != nil {
+				t.Fatalf("unexpected error occurred: %v", err)
+			}
+			schema, err := paths["apis/apps/v1"].Schema(runtime.ContentTypeJSON)
+			if err != nil {
+				t.Fatalf("unexpected error occurred: %v", err)
+			}
+			expectedResult := `{"openapi":"3.0.0","info":{"title":"Kubernetes","version":"unversioned"}}`
+			if string(schema) != expectedResult {
+				t.Fatalf("unexpected result actual: %s expected: %s", string(schema), expectedResult)
+			}
+		})
+	}
+}

util/cert/cert.go

@@ -25,6 +25,7 @@ import (
 	"crypto/x509/pkix"
 	"encoding/pem"
 	"fmt"
+	"math"
 	"math/big"
 	"net"
 	"os"
@@ -57,8 +58,14 @@ type AltNames struct {
 // NewSelfSignedCACert creates a CA certificate
 func NewSelfSignedCACert(cfg Config, key crypto.Signer) (*x509.Certificate, error) {
 	now := time.Now()
+	// returns a uniform random value in [0, max-1), then add 1 to serial to make it a uniform random value in [1, max).
+	serial, err := cryptorand.Int(cryptorand.Reader, new(big.Int).SetInt64(math.MaxInt64-1))
+	if err != nil {
+		return nil, err
+	}
+	serial = new(big.Int).Add(serial, big.NewInt(1))
 	tmpl := x509.Certificate{
-		SerialNumber: new(big.Int).SetInt64(0),
+		SerialNumber: serial,
 		Subject: pkix.Name{
 			CommonName:   cfg.CommonName,
 			Organization: cfg.Organization,
@@ -116,9 +123,14 @@ func GenerateSelfSignedCertKeyWithFixtures(host string, alternateIPs []net.IP, a
 	if err != nil {
 		return nil, nil, err
 	}
-
+	// returns a uniform random value in [0, max-1), then add 1 to serial to make it a uniform random value in [1, max).
+	serial, err := cryptorand.Int(cryptorand.Reader, new(big.Int).SetInt64(math.MaxInt64-1))
+	if err != nil {
+		return nil, nil, err
+	}
+	serial = new(big.Int).Add(serial, big.NewInt(1))
 	caTemplate := x509.Certificate{
-		SerialNumber: big.NewInt(1),
+		SerialNumber: serial,
 		Subject: pkix.Name{
 			CommonName: fmt.Sprintf("%s-ca@%d", host, time.Now().Unix()),
 		},
@@ -144,9 +156,14 @@ func GenerateSelfSignedCertKeyWithFixtures(host string, alternateIPs []net.IP, a
 	if err != nil {
 		return nil, nil, err
 	}
-
+	// returns a uniform random value in [0, max-1), then add 1 to serial to make it a uniform random value in [1, max).
+	serial, err = cryptorand.Int(cryptorand.Reader, new(big.Int).SetInt64(math.MaxInt64-1))
+	if err != nil {
+		return nil, nil, err
+	}
+	serial = new(big.Int).Add(serial, big.NewInt(1))
 	template := x509.Certificate{
-		SerialNumber: big.NewInt(2),
+		SerialNumber: serial,
 		Subject: pkix.Name{
 			CommonName: fmt.Sprintf("%s@%d", host, time.Now().Unix()),
 		},