feat(version): add version message mechanism

This gives us an easy to use way to communicate with users for specific
version periods.

Fixes: #1555

go.mod

@@ -51,6 +51,7 @@ require (
 	github.com/google/gofuzz v1.2.0 // indirect
 	github.com/google/pprof v0.0.0-20230323073829-e72429f035bd // indirect
 	github.com/google/uuid v1.3.1 // indirect
+	github.com/hashicorp/go-version v1.6.0 // indirect
 	github.com/hashicorp/hcl v1.0.0 // indirect
 	github.com/imdario/mergo v0.3.16 // indirect
 	github.com/jmespath/go-jmespath v0.4.0 // indirect

go.sum

@@ -96,6 +96,7 @@ github.com/fsnotify/fsnotify v1.6.0/go.mod h1:sl3t1tCWJFWoRz9R8WJCbQihKKwmorjAbS
 github.com/go-gl/glfw v0.0.0-20190409004039-e6da0acd62b1/go.mod h1:vR7hzQXu2zJy9AVAgeJqvqgH9Q5CA+iKCZ2gyEVpxRU=
 github.com/go-gl/glfw/v3.3/glfw v0.0.0-20191125211704-12ad95a8df72/go.mod h1:tQ2UAYgL5IevRw8kRxooKSPJfGvJ9fJQFa0TUsXzTg8=
 github.com/go-gl/glfw/v3.3/glfw v0.0.0-20200222043503-6f7a984d4dc4/go.mod h1:tQ2UAYgL5IevRw8kRxooKSPJfGvJ9fJQFa0TUsXzTg8=
+github.com/go-logfmt/logfmt v0.5.1/go.mod h1:WYhtIu8zTZfxdn5+rREduYbwxfcBr/Vr6KEVveWlfTs=
 github.com/go-logr/logr v1.2.0/go.mod h1:jdQByPbusPIv2/zmleS9BjJVeZ6kBagPoEUsqbVz/1A=
 github.com/go-logr/logr v1.2.4 h1:g01GSCwiDw2xSZfjJ2/T9M+S6pFdcNtFYsp+Y43HYDQ=
 github.com/go-logr/logr v1.2.4/go.mod h1:jdQByPbusPIv2/zmleS9BjJVeZ6kBagPoEUsqbVz/1A=
@@ -183,6 +184,8 @@ github.com/google/uuid v1.3.1/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+
 github.com/googleapis/gax-go/v2 v2.0.4/go.mod h1:0Wqv26UfaUD9n4G6kQubkQ+KchISgw+vpHVxEJEs9eg=
 github.com/googleapis/gax-go/v2 v2.0.5/go.mod h1:DWXyrwAJ9X0FpwwEdw+IPEYBICEFu5mhpdKc/us6bOk=
 github.com/googleapis/google-cloud-go-testing v0.0.0-20200911160855-bcd43fbb19e8/go.mod h1:dvDLG8qkwmyD9a/MJJN3XJcT3xFxOKAvTZGvuZmac9g=
+github.com/hashicorp/go-version v1.6.0 h1:feTTfFNnjP967rlCxM/I9g701jU+RN74YKx2mOkIeek=
+github.com/hashicorp/go-version v1.6.0/go.mod h1:fltr4n8CU8Ke44wwGCBoEymUuxUHl09ZGVZPK5anwXA=
 github.com/hashicorp/golang-lru v0.5.0/go.mod h1:/m3WP610KZHVQ1SGc6re/UDhFvYD7pJ4Ao+sR/qLZy8=
 github.com/hashicorp/golang-lru v0.5.1/go.mod h1:/m3WP610KZHVQ1SGc6re/UDhFvYD7pJ4Ao+sR/qLZy8=
 github.com/hashicorp/hcl v1.0.0 h1:0Anlzjpi4vEasTeNFn2mLJgTSwt0+6sfsiTG8qcWGx4=
@@ -198,10 +201,12 @@ github.com/jmespath/go-jmespath/internal/testify v1.5.1 h1:shLQSRRSCCPj3f2gpwzGw
 github.com/jmespath/go-jmespath/internal/testify v1.5.1/go.mod h1:L3OGu8Wl2/fWfCI6z80xFu9LTZmf1ZRjMHUOPmWr69U=
 github.com/josharian/intern v1.0.0 h1:vlS4z54oSdjm0bgjRigI+G1HpF+tI+9rE5LLzOg8HmY=
 github.com/josharian/intern v1.0.0/go.mod h1:5DoeVV0s6jJacbCEi61lwdGj/aVlrQvzHFFd8Hwg//Y=
+github.com/jpillora/backoff v1.0.0/go.mod h1:J/6gKK9jxlEcS3zixgDgUAsiuZ7yrSoa/FX5e0EB2j4=
 github.com/json-iterator/go v1.1.12 h1:PV8peI4a0ysnczrg+LtxykD8LfKY9ML6u2jnxaEnrnM=
 github.com/json-iterator/go v1.1.12/go.mod h1:e30LSqwooZae/UwlEbR2852Gd8hjQvJoHmT4TnhNGBo=
 github.com/jstemmer/go-junit-report v0.0.0-20190106144839-af01ea7f8024/go.mod h1:6v2b51hI/fHJwM22ozAgKL4VKDeJcHhJFhtBdhmNjmU=
 github.com/jstemmer/go-junit-report v0.9.1/go.mod h1:Brl9GWCQeLvo8nXZwPNNblvFj/XSXhF0NWZEnDohbsk=
+github.com/julienschmidt/httprouter v1.3.0/go.mod h1:JR6WtHb+2LUe8TCKY3cZOxFyyO8IZAc4RVcycCCAKdM=
 github.com/k-sone/critbitgo v1.4.0 h1:l71cTyBGeh6X5ATh6Fibgw3+rtNT80BA0uNNWgkPrbE=
 github.com/k-sone/critbitgo v1.4.0/go.mod h1:7E6pyoyADnFxlUBEKcnfS49b7SUAQGMK+OAp/UQvo0s=
 github.com/kisielk/errcheck v1.5.0/go.mod h1:pFxgyoBC7bSaBwPgfKdkLd5X25qrDl4LWUI2bnpBCr8=
@@ -235,6 +240,7 @@ github.com/morikuni/aec v1.0.0 h1:nP9CBfwrvYnBRgY6qfDQkygYDmYwOilePFkwzv4dU8A=
 github.com/morikuni/aec v1.0.0/go.mod h1:BbKIizmSmc5MMPqRYbxO4ZU0S0+P200+tUnFx7PXmsc=
 github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 h1:C3w9PqII01/Oq1c1nUAm88MOHcQC9l5mIlSMApZMrHA=
 github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822/go.mod h1:+n7T8mK8HuQTcFwEeznm/DIxMOiR9yIdICNftLE1DvQ=
+github.com/mwitkow/go-conntrack v0.0.0-20190716064945-2f068394615f/go.mod h1:qRWi+5nqEBWmkhHvq77mSJWrCKwh8bxhgT7d/eI7P4U=
 github.com/nxadm/tail v1.4.4/go.mod h1:kenIhsEOeOJmVchQTgglprH7qJGnHDVpk1VPCcaMI8A=
 github.com/nxadm/tail v1.4.8 h1:nPr65rt6Y5JFSKQO7qToXr7pePgD6Gwiw05lkbyAQTE=
 github.com/nxadm/tail v1.4.8/go.mod h1:+ncqLTQzXmGhMZNUePPaPqPvBxHAIsmXswZKocGu+AU=

pkg/cmd/kube-router.go

@@ -39,6 +39,7 @@ func NewKubeRouterDefault(config *options.KubeRouterConfig) (*KubeRouter, error)
 	var clientconfig *rest.Config
 	var err error
 	version.PrintVersion(true)
+	version.PrintVersionMessages(true)
 	// Use out of cluster config if the URL or kubeconfig have been specified. Otherwise use incluster config.
 	if len(config.Master) != 0 || len(config.Kubeconfig) != 0 {
 		clientconfig, err = clientcmd.BuildConfigFromFlags(config.Master, config.Kubeconfig)

pkg/version/version.go

@@ -5,16 +5,61 @@ import (
 	"os"
 	"runtime"
 
+	"github.com/hashicorp/go-version"
 	"k8s.io/klog/v2"
 )
 
+type versionMessage struct {
+	minVersionInclusive string
+	maxVersionExclusive string
+	message             string
+}
+
 // Version and BuildDate are injected at build time via ldflags
-var Version string
-var BuildDate string
+var (
+	BuildDate string
+	Version   string
+
+	msgVersionArr = []versionMessage{
+		{
+			minVersionInclusive: "v2.0.0",
+			maxVersionExclusive: "v2.1.0",
+			message: "Version v2.X introduces backward compatibility breaking changes, the kube-router project " +
+				"recommends that you read the release notes carefully before deploying: " +
+				"https://github.com/cloudnativelabs/kube-router/releases/tag/v2.0.0",
+		},
+	}
+)
+
+func (ver versionMessage) versionApplicable(testVerStr string) bool {
+	minVer, err1 := version.NewVersion(ver.minVersionInclusive)
+	maxVer, err2 := version.NewVersion(ver.maxVersionExclusive)
+	testVer, err3 := version.NewVersion(testVerStr)
+
+	// When in doubt return false
+	if err1 != nil || err2 != nil || err3 != nil {
+		klog.Warningf("encountered an error while trying to parse version numbers: %v - %v - %v", err1, err2, err3)
+		return false
+	}
+
+	return testVer.GreaterThanOrEqual(minVer) && testVer.LessThan(maxVer)
+}
 
 func PrintVersion(logOutput bool) {
 	output := fmt.Sprintf("Running %v version %s, built on %s, %s\n", os.Args[0], Version, BuildDate, runtime.Version())
 
+	outputToStream(output, logOutput)
+}
+
+func PrintVersionMessages(logOutput bool) {
+	for _, verMsg := range msgVersionArr {
+		if verMsg.versionApplicable(Version) {
+			outputToStream(verMsg.message, logOutput)
+		}
+	}
+}
+
+func outputToStream(output string, logOutput bool) {
 	if !logOutput {
 		_, _ = fmt.Fprintf(os.Stderr, "%s", output)
 	} else {