Add warning if client/server version difference exceeds the supported skew

Kubernetes-commit: 0c28cad8d142059b488347badd46433d50e47feb

pkg/cmd/version/skew_warning.go

@@ -0,0 +1,54 @@
+/*
+Copyright 2021 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 version
+
+import (
+	"fmt"
+	"io"
+	"k8s.io/apimachinery/pkg/util/version"
+	apimachineryversion "k8s.io/apimachinery/pkg/version"
+	"math"
+)
+
+// supportedMinorVersionSkew is the maximum supported difference between the client and server minor versions.
+// For example: client versions 1.18, 1.19, and 1.20 would be within the supported version skew for server version 1.19,
+// and server versions 1.18, 1.19, and 1.20 would be within the supported version skew for client version 1.19.
+const supportedMinorVersionSkew = 1
+
+// printVersionSkewWarning prints a warning message if the difference between the client and version is greater than
+// the supported version skew.
+func printVersionSkewWarning(w io.Writer, clientVersion, serverVersion apimachineryversion.Info) error {
+	parsedClientVersion, err := version.ParseSemantic(clientVersion.GitVersion)
+	if err != nil {
+		return err
+	}
+
+	parsedServerVersion, err := version.ParseSemantic(serverVersion.GitVersion)
+	if err != nil {
+		return err
+	}
+
+	majorVersionDifference := math.Abs(float64(parsedClientVersion.Major()) - float64(parsedServerVersion.Major()))
+	minorVersionDifference := math.Abs(float64(parsedClientVersion.Minor()) - float64(parsedServerVersion.Minor()))
+
+	if majorVersionDifference > 0 || minorVersionDifference > supportedMinorVersionSkew {
+		fmt.Fprintf(w, "WARNING: version difference between client (%d.%d) and server (%d.%d) exceeds the supported minor version skew of +/-%d\n",
+			parsedClientVersion.Major(), parsedClientVersion.Minor(), parsedServerVersion.Major(), parsedServerVersion.Minor(), supportedMinorVersionSkew)
+	}
+
+	return nil
+}

pkg/cmd/version/skew_warning_test.go

@@ -0,0 +1,96 @@
+/*
+Copyright 2021 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 version
+
+import (
+	"bytes"
+	apimachineryversion "k8s.io/apimachinery/pkg/version"
+	"testing"
+)
+
+func TestPrintVersionSkewWarning(t *testing.T) {
+	output := &bytes.Buffer{}
+
+	testCases := []struct {
+		name              string
+		clientVersion     apimachineryversion.Info
+		serverVersion     apimachineryversion.Info
+		isWarningExpected bool
+	}{
+		{
+			name:              "Should not warn if server and client versions are same",
+			clientVersion:     apimachineryversion.Info{GitVersion: "v1.19.1"},
+			serverVersion:     apimachineryversion.Info{GitVersion: "v1.19.1"},
+			isWarningExpected: false,
+		},
+		{
+			name:              "Should not warn if server and client versions are same and server is alpha",
+			clientVersion:     apimachineryversion.Info{GitVersion: "v1.19.1"},
+			serverVersion:     apimachineryversion.Info{GitVersion: "v1.19.7-alpha"},
+			isWarningExpected: false,
+		},
+		{
+			name:              "Should not warn if server and client versions are same and server is beta",
+			clientVersion:     apimachineryversion.Info{GitVersion: "v1.19.1"},
+			serverVersion:     apimachineryversion.Info{GitVersion: "v1.19.7-beta"},
+			isWarningExpected: false,
+		},
+		{
+			name:              "Should not warn if server is 1 minor version ahead of client",
+			clientVersion:     apimachineryversion.Info{GitVersion: "v1.18.5"},
+			serverVersion:     apimachineryversion.Info{GitVersion: "v1.19.1"},
+			isWarningExpected: false,
+		},
+		{
+			name:              "Should not warn if server is 1 minor version behind client",
+			clientVersion:     apimachineryversion.Info{GitVersion: "v1.19.1"},
+			serverVersion:     apimachineryversion.Info{GitVersion: "v1.18.5"},
+			isWarningExpected: false,
+		},
+		{
+			name:              "Should warn if server is 2 minor versions ahead of client",
+			clientVersion:     apimachineryversion.Info{GitVersion: "v1.17.7"},
+			serverVersion:     apimachineryversion.Info{GitVersion: "v1.19.1"},
+			isWarningExpected: true,
+		},
+		{
+			name:              "Should warn if server is 2 minor versions behind client",
+			clientVersion:     apimachineryversion.Info{GitVersion: "v1.19.1"},
+			serverVersion:     apimachineryversion.Info{GitVersion: "v1.17.7"},
+			isWarningExpected: true,
+		},
+		{
+			name:              "Should warn if major versions are not equal",
+			clientVersion:     apimachineryversion.Info{GitVersion: "v1.19.1"},
+			serverVersion:     apimachineryversion.Info{GitVersion: "v2.19.1"},
+			isWarningExpected: true,
+		},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			output.Reset()
+
+			printVersionSkewWarning(output, tc.clientVersion, tc.serverVersion)
+
+			if tc.isWarningExpected && output.Len() == 0 {
+				t.Error("warning was expected, but not written to the output")
+			} else if !tc.isWarningExpected && output.Len() > 0 {
+				t.Errorf("warning was not expected, but was written to the output: %s", output.String())
+			}
+		})
+	}
+}

pkg/cmd/version/version.go

@@ -158,5 +158,11 @@ func (o *Options) Run() error {
 		return fmt.Errorf("VersionOptions were not validated: --output=%q should have been rejected", o.Output)
 	}
 
+	if serverVersion != nil {
+		if err := printVersionSkewWarning(o.ErrOut, clientVersion, *serverVersion); err != nil {
+			return err
+		}
+	}
+
 	return serverErr
 }