Show FCV validation error before applying changes (#621)

# Summary

Previously applying the faulty `spec.featureCompatibilityVersion`, but
having two items separated by "." would make validation pass. Example of
incorrect, but allowed `spec.featureCompatibilityVersion` - "8.abc".
Fortunately, later during [AC
update](https://github.com/mongodb/mongodb-kubernetes/blob/f0050b8942545701e8cb9e42d54d14f0cb58ee6a/mongodb-community-operator/pkg/automationconfig/automation_config_builder.go#L271-L276)
we would still throw an error, but the changes would be applied.


https://github.com/mongodb/mongodb-kubernetes/blob/f0050b8942545701e8cb9e42d54d14f0cb58ee6a/mongodb-community-operator/pkg/automationconfig/automation_config_builder.go#L271-L276

This change adds the missing semver validation for
`spec.featureCompatibilityVersion` (including appDB).

## Proof of Work

Passing updated unit tests.

## Checklist

- [ ] Have you linked a jira ticket and/or is the ticket in the title?
- [x] Have you checked whether your jira ticket required DOCSP changes?
- [x] Have you added changelog file?
    - use `skip-changelog` label if not needed
- refer to [Changelog files and Release
Notes](https://github.com/mongodb/mongodb-kubernetes/blob/master/CONTRIBUTING.md#changelog-files-and-release-notes)
section in CONTRIBUTING.md for more details

Author: MaciejKaras

api/v1/mdb/mongodb_types.go

@@ -688,10 +688,10 @@ func (m *MongoDbSpec) GetClusterDomain() string {
 
 func (m *MongoDbSpec) MinimumMajorVersion() uint64 {
 	if m.FeatureCompatibilityVersion != nil && *m.FeatureCompatibilityVersion != "" {
-		fcv := *m.FeatureCompatibilityVersion
+		fcvString := *m.FeatureCompatibilityVersion
 
 		// ignore errors here as the format of FCV/version is handled by CRD validation
-		semverFcv, _ := semver.Make(fmt.Sprintf("%s.0", fcv))
+		semverFcv, _ := fcv.FeatureCompatibilityVersionToSemverFormat(fcvString)
 		return semverFcv.Major
 	}
 	semverVersion, _ := semver.Make(m.GetMongoDBVersion())

api/v1/mdb/mongodb_validation.go

@@ -12,6 +12,7 @@ import (
 
 	v1 "github.com/mongodb/mongodb-kubernetes/api/v1"
 	"github.com/mongodb/mongodb-kubernetes/api/v1/status"
+	"github.com/mongodb/mongodb-kubernetes/pkg/fcv"
 	"github.com/mongodb/mongodb-kubernetes/pkg/multicluster"
 	"github.com/mongodb/mongodb-kubernetes/pkg/util"
 	"github.com/mongodb/mongodb-kubernetes/pkg/util/stringutil"
@@ -430,15 +431,21 @@ func featureCompatibilityVersionValidation(d DbCommonSpec) v1.ValidationResult {
 	return ValidateFCV(fcv)
 }
 
-func ValidateFCV(fcv *string) v1.ValidationResult {
-	if fcv != nil {
-		f := *fcv
-		if f == util.AlwaysMatchVersionFCV {
+func ValidateFCV(fcvStringPointer *string) v1.ValidationResult {
+	if fcvStringPointer != nil {
+		fcvString := *fcvStringPointer
+		if fcvString == util.AlwaysMatchVersionFCV {
 			return v1.ValidationSuccess()
 		}
-		splitted := strings.Split(f, ".")
+
+		splitted := strings.Split(fcvString, ".")
 		if len(splitted) != 2 {
-			return v1.ValidationError("invalid feature compatibility version: %s, possible values are: '%s' or 'major.minor'", f, util.AlwaysMatchVersionFCV)
+			return v1.ValidationError("invalid feature compatibility version %q, possible values are: '%s' or 'major.minor'", fcvString, util.AlwaysMatchVersionFCV)
+		}
+
+		_, err := fcv.FeatureCompatibilityVersionToSemverFormat(fcvString)
+		if err != nil {
+			return v1.ValidationError("invalid feature compatibility version %q: %s", fcvString, err)
 		}
 	}
 	return v1.ValidationResult{}

api/v1/mdb/mongodb_validation_test.go

@@ -244,7 +244,7 @@ func TestReplicasetFCV(t *testing.T) {
 			name:                 "Invalid FCV value",
 			fcv:                  ptr.To("test"),
 			expectError:          true,
-			expectedErrorMessage: "invalid feature compatibility version: test, possible values are: 'AlwaysMatchVersion' or 'major.minor'",
+			expectedErrorMessage: "invalid feature compatibility version \"test\", possible values are: 'AlwaysMatchVersion' or 'major.minor'",
 		},
 		{
 			name:        "Valid FCV with specific version",
@@ -255,7 +255,13 @@ func TestReplicasetFCV(t *testing.T) {
 			name:                 "Invalid FCV - not major.minor only",
 			fcv:                  ptr.To("4.0.0"),
 			expectError:          true,
-			expectedErrorMessage: "invalid feature compatibility version: 4.0.0, possible values are: 'AlwaysMatchVersion' or 'major.minor'",
+			expectedErrorMessage: "invalid feature compatibility version \"4.0.0\", possible values are: 'AlwaysMatchVersion' or 'major.minor'",
+		},
+		{
+			name:                 "Invalid FCV - not major leading 0",
+			fcv:                  ptr.To("4.01"),
+			expectError:          true,
+			expectedErrorMessage: "invalid feature compatibility version \"4.01\": Minor number must not contain leading zeroes \"01\"",
 		},
 		{
 			name:        "Valid FCV with AlwaysMatchVersion",

api/v1/mdbmulti/mongodb_multi_types.go

@@ -535,10 +535,10 @@ func (m *MongoDBMultiSpec) GetMemberOptions() []automationconfig.MemberOptions {
 
 func (m *MongoDBMultiSpec) MinimumMajorVersion() uint64 {
 	if m.FeatureCompatibilityVersion != nil && *m.FeatureCompatibilityVersion != "" {
-		fcv := *m.FeatureCompatibilityVersion
+		fcvString := *m.FeatureCompatibilityVersion
 
 		// ignore errors here as the format of FCV/version is handled by CRD validation
-		semverFcv, _ := semver.Make(fmt.Sprintf("%s.0", fcv))
+		semverFcv, _ := fcv.FeatureCompatibilityVersionToSemverFormat(fcvString)
 		return semverFcv.Major
 	}
 	semverVersion, _ := semver.Make(m.GetMongoDBVersion())

changelog/20251202_fix_improve_validation_for_fcv.md

@@ -0,0 +1,8 @@
+---
+kind: fix
+date: 2025-12-02
+---
+
+* **MongoDB**, **MongoDBOpsManager**: Improve validation for `featureCompatibilityVersion` field in `MongoDB` and `MongoDBOpsManager` spec.
+  The field now enforces proper semantic versioning. Previously, invalid semver values could be accepted,
+  potentially resulting in incorrect configurations.

controllers/om/deployment.go

@@ -15,6 +15,7 @@ import (
 	mdbv1 "github.com/mongodb/mongodb-kubernetes/api/v1/mdb"
 	mdbcv1 "github.com/mongodb/mongodb-kubernetes/mongodb-community-operator/api/v1"
 	"github.com/mongodb/mongodb-kubernetes/mongodb-community-operator/pkg/automationconfig"
+	"github.com/mongodb/mongodb-kubernetes/pkg/fcv"
 	"github.com/mongodb/mongodb-kubernetes/pkg/tls"
 	"github.com/mongodb/mongodb-kubernetes/pkg/util"
 	"github.com/mongodb/mongodb-kubernetes/pkg/util/maputil"
@@ -493,8 +494,8 @@ func (d Deployment) MinimumMajorVersion() uint64 {
 	minimumMajorVersion := semver.Version{Major: math.MaxUint64}
 	for _, p := range d.getProcesses() {
 		if p.FeatureCompatibilityVersion() != "" {
-			fcv := fmt.Sprintf("%s.0", util.StripEnt(p.FeatureCompatibilityVersion()))
-			semverFcv, _ := semver.Make(fcv)
+			fcvString := util.StripEnt(p.FeatureCompatibilityVersion())
+			semverFcv, _ := fcv.FeatureCompatibilityVersionToSemverFormat(fcvString)
 			if semverFcv.LE(minimumMajorVersion) {
 				minimumMajorVersion = semverFcv
 			}

pkg/fcv/fcv.go

@@ -1,6 +1,12 @@
 package fcv
 
-import "github.com/mongodb/mongodb-kubernetes/pkg/util"
+import (
+	"fmt"
+
+	"github.com/blang/semver"
+
+	"github.com/mongodb/mongodb-kubernetes/pkg/util"
+)
 
 func CalculateFeatureCompatibilityVersion(currentVersionFromCR string, fcvFromStatus string, fcvFromCR *string) string {
 	majorMinorVersionFromCR, setVersion, _ := util.MajorMinorVersion(currentVersionFromCR)
@@ -44,3 +50,7 @@ func CalculateFeatureCompatibilityVersion(currentVersionFromCR string, fcvFromSt
 
 	return lastAppliedMajorMinorVersion
 }
+
+func FeatureCompatibilityVersionToSemverFormat(fcv string) (semver.Version, error) {
+	return semver.Make(fmt.Sprintf("%s.0", fcv))
+}