kube-proxy: remove ipvs-to-iptables fallback

If the user passes "--proxy-mode ipvs", and it is not possible to use
IPVS, then error out rather than falling back to iptables.

There was never any good reason to be doing fallback; this was
presumably erroneously added to parallel the iptables-to-userspace
fallback (which only existed because we had wanted iptables to be the
default but not all systems could support it).

In particular, if the user passed configuration options for ipvs, then
they presumably *didn't* pass configuration options for iptables, and
so even if the iptables proxy is able to run, it is likely to be
misconfigured.

pkg/proxy/ipvs/proxier.go

@@ -706,25 +706,25 @@ func (handle *LinuxKernelHandler) GetKernelVersion() (string, error) {
 	return strings.TrimSpace(string(fileContent)), nil
 }
 
-// CanUseIPVSProxier returns true if we can use the ipvs Proxier.
+// CanUseIPVSProxier checks if we can use the ipvs Proxier.
 // This is determined by checking if all the required kernel modules can be loaded. It may
 // return an error if it fails to get the kernel modules information without error, in which
 // case it will also return false.
-func CanUseIPVSProxier(handle KernelHandler, ipsetver IPSetVersioner, scheduler string) (bool, error) {
+func CanUseIPVSProxier(handle KernelHandler, ipsetver IPSetVersioner, scheduler string) error {
 	mods, err := handle.GetModules()
 	if err != nil {
-		return false, fmt.Errorf("error getting installed ipvs required kernel modules: %v", err)
+		return fmt.Errorf("error getting installed ipvs required kernel modules: %v", err)
 	}
 	loadModules := sets.NewString()
 	loadModules.Insert(mods...)
 
 	kernelVersionStr, err := handle.GetKernelVersion()
 	if err != nil {
-		return false, fmt.Errorf("error determining kernel version to find required kernel modules for ipvs support: %v", err)
+		return fmt.Errorf("error determining kernel version to find required kernel modules for ipvs support: %v", err)
 	}
 	kernelVersion, err := version.ParseGeneric(kernelVersionStr)
 	if err != nil {
-		return false, fmt.Errorf("error parsing kernel version %q: %v", kernelVersionStr, err)
+		return fmt.Errorf("error parsing kernel version %q: %v", kernelVersionStr, err)
 	}
 	mods = utilipvs.GetRequiredIPVSModules(kernelVersion)
 	wantModules := sets.NewString()
@@ -751,18 +751,18 @@ func CanUseIPVSProxier(handle KernelHandler, ipsetver IPSetVersioner, scheduler
 	}
 
 	if len(missingMods) != 0 {
-		return false, fmt.Errorf("IPVS proxier will not be used because the following required kernel modules are not loaded: %v", missingMods)
+		return fmt.Errorf("IPVS proxier will not be used because the following required kernel modules are not loaded: %v", missingMods)
 	}
 
 	// Check ipset version
 	versionString, err := ipsetver.GetVersion()
 	if err != nil {
-		return false, fmt.Errorf("error getting ipset version, error: %v", err)
+		return fmt.Errorf("error getting ipset version, error: %v", err)
 	}
 	if !checkMinVersion(versionString) {
-		return false, fmt.Errorf("ipset version: %s is less than min required version: %s", versionString, MinIPSetCheckVersion)
+		return fmt.Errorf("ipset version: %s is less than min required version: %s", versionString, MinIPSetCheckVersion)
 	}
-	return true, nil
+	return nil
 }
 
 // CleanupIptablesLeftovers removes all iptables rules and chains created by the Proxier

pkg/proxy/ipvs/proxier_test.go

@@ -364,9 +364,9 @@ func TestCanUseIPVSProxier(t *testing.T) {
 	for i := range testCases {
 		handle := &fakeKernelHandler{modules: testCases[i].mods, kernelVersion: testCases[i].kernelVersion}
 		versioner := &fakeIPSetVersioner{version: testCases[i].ipsetVersion, err: testCases[i].ipsetErr}
-		ok, err := CanUseIPVSProxier(handle, versioner, testCases[i].scheduler)
-		if ok != testCases[i].ok {
-			t.Errorf("Case [%d], expect %v, got %v: err: %v", i, testCases[i].ok, ok, err)
+		err := CanUseIPVSProxier(handle, versioner, testCases[i].scheduler)
+		if (err == nil) != testCases[i].ok {
+			t.Errorf("Case [%d], expect %v, got err: %v", i, testCases[i].ok, err)
 		}
 	}
 }