ic: allow multi-arch clusters for AWS when feature gate enabled

This is the first step to implement multi-arch clusters for AWS: allow
users to specify a different architecture for compute nodes when the
`MultiArchInstallAWS` feature gate is enabled.

Author: r4f4

pkg/types/installconfig.go

@@ -578,6 +578,16 @@ func ClusterAPIFeatureGateEnabled(platform string, fgs featuregates.FeatureGate)
 	}
 }
 
+// MultiArchFeatureGateEnabled checks whether feature gate enabling multi-arch clusters is enabled.
+func MultiArchFeatureGateEnabled(platform string, fgs featuregates.FeatureGate) bool {
+	switch platform {
+	case aws.Name:
+		return fgs.Enabled(features.FeatureGateMultiArchInstallAWS)
+	default:
+		return false
+	}
+}
+
 // PublicAPI indicates whether the API load balancer should be public
 // by inspecting the cluster and operator publishing strategies.
 func (c *InstallConfig) PublicAPI() bool {

pkg/types/validation/installconfig.go

@@ -124,7 +124,8 @@ func ValidateInstallConfig(c *types.InstallConfig, usingAgentMethod bool) field.
 	} else {
 		allErrs = append(allErrs, field.Required(field.NewPath("controlPlane"), "controlPlane is required"))
 	}
-	allErrs = append(allErrs, validateCompute(&c.Platform, c.ControlPlane, c.Compute, field.NewPath("compute"))...)
+	multiArchEnabled := types.MultiArchFeatureGateEnabled(c.Platform.Name(), c.EnabledFeatureGates())
+	allErrs = append(allErrs, validateCompute(&c.Platform, c.ControlPlane, c.Compute, field.NewPath("compute"), multiArchEnabled)...)
 	if err := validate.ImagePullSecret(c.PullSecret); err != nil {
 		allErrs = append(allErrs, field.Invalid(field.NewPath("pullSecret"), c.PullSecret, err.Error()))
 	}
@@ -606,7 +607,7 @@ func validateComputeEdge(platform *types.Platform, pName string, fldPath *field.
 	return allErrs
 }
 
-func validateCompute(platform *types.Platform, control *types.MachinePool, pools []types.MachinePool, fldPath *field.Path) field.ErrorList {
+func validateCompute(platform *types.Platform, control *types.MachinePool, pools []types.MachinePool, fldPath *field.Path, isMultiArchEnabled bool) field.ErrorList {
 	allErrs := field.ErrorList{}
 	poolNames := map[string]bool{}
 	for i, p := range pools {
@@ -623,7 +624,7 @@ func validateCompute(platform *types.Platform, control *types.MachinePool, pools
 			allErrs = append(allErrs, field.Duplicate(poolFldPath.Child("name"), p.Name))
 		}
 		poolNames[p.Name] = true
-		if control != nil && control.Architecture != p.Architecture {
+		if control != nil && control.Architecture != p.Architecture && !isMultiArchEnabled {
 			allErrs = append(allErrs, field.Invalid(poolFldPath.Child("architecture"), p.Architecture, "heteregeneous multi-arch is not supported; compute pool architecture must match control plane"))
 		}
 		allErrs = append(allErrs, ValidateMachinePool(platform, &p, poolFldPath)...)

pkg/types/validation/installconfig_test.go

@@ -1413,6 +1413,16 @@ func TestValidateInstallConfig(t *testing.T) {
 			}(),
 			expectedError: `^compute\[0\].architecture: Invalid value: "arm64": heteregeneous multi-arch is not supported; compute pool architecture must match control plane$`,
 		},
+		{
+			name: "aws cluster is heteregeneous",
+			installConfig: func() *types.InstallConfig {
+				c := validInstallConfig()
+				c.Compute[0].Architecture = types.ArchitectureARM64
+				c.FeatureSet = "CustomNoUpgrade"
+				c.FeatureGates = []string{"MultiArchInstallAWS=true"}
+				return c
+			}(),
+		},
 		{
 			name: "valid cloud credentials mode",
 			installConfig: func() *types.InstallConfig {