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separate arbiter and members resource creation #417

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52be55d
separate arbiter and members resource creation
Sep 7, 2025
ca3371b
create changelog
Sep 7, 2025
6b2dbbc
Merge branch 'master' into arbiter-statefullset-separation-default-co…
sina-grz Sep 7, 2025
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12 changes: 12 additions & 0 deletions changelog/20250907_fix_separate_arbiter_and_members_resources.md
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@@ -0,0 +1,12 @@
---
title: Separate arbiter and members resources
kind: fix
date: 2025-09-07
---

**Issue:** Previously, arbiter StatefulSets were incorrectly using the same resource specifications as data-bearing members, which could lead to resource over-allocation or under-allocation for arbiters that have different resource requirements.
- Separated resource creation logic for arbiters and data-bearing members
- Implemented a default resource template specifically for arbiter nodes
- Arbiters now use their own StatefulSet configuration instead of inheriting from `spec.statefulSet`
- This ensures arbiters receive appropriate resource allocation based on their lighter workload requirements

41 changes: 25 additions & 16 deletions mongodb-community-operator/controllers/construct/mongodbstatefulset.go
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Expand Up @@ -120,7 +120,7 @@ type MongoDBStatefulSetOwner interface {
// BuildMongoDBReplicaSetStatefulSetModificationFunction builds the parts of the replica set that are common between every resource that implements
// MongoDBStatefulSetOwner.
// It doesn't configure TLS or additional containers/env vars that the statefulset might need.
func BuildMongoDBReplicaSetStatefulSetModificationFunction(mdb MongoDBStatefulSetOwner, scaler scale.ReplicaSetScaler, mongodbImage, agentImage, versionUpgradeHookImage, readinessProbeImage string, withInitContainers bool, initAppDBImage string) statefulset.Modification {
func BuildMongoDBReplicaSetStatefulSetModificationFunction(mdb MongoDBStatefulSetOwner, scaler scale.ReplicaSetScaler, mongodbImage, agentImage, versionUpgradeHookImage, readinessProbeImage string, withInitContainers bool, initAppDBImage string, isArbiter bool) statefulset.Modification {
labels := map[string]string{
"app": mdb.ServiceName(),
}
Expand Down Expand Up @@ -186,21 +186,8 @@ func BuildMongoDBReplicaSetStatefulSetModificationFunction(mdb MongoDBStatefulSe
dataVolumeClaim := statefulset.NOOP()
logVolumeClaim := statefulset.NOOP()
singleModeVolumeClaim := func(s *appsv1.StatefulSet) {}
if mdb.HasSeparateDataAndLogsVolumes() {
logVolumeMount := statefulset.CreateVolumeMount(mdb.LogsVolumeName(), automationconfig.DefaultAgentLogPath)
dataVolumeMount := statefulset.CreateVolumeMount(mdb.DataVolumeName(), mdb.GetMongodConfiguration().GetDBDataDir())
dataVolumeClaim = statefulset.WithVolumeClaim(mdb.DataVolumeName(), dataPvc(mdb.DataVolumeName()))
logVolumeClaim = statefulset.WithVolumeClaim(mdb.LogsVolumeName(), logsPvc(mdb.LogsVolumeName()))
mongodbAgentVolumeMounts = append(mongodbAgentVolumeMounts, dataVolumeMount, logVolumeMount)
mongodVolumeMounts = append(mongodVolumeMounts, dataVolumeMount, logVolumeMount)
} else {
mounts := []corev1.VolumeMount{
statefulset.CreateVolumeMount(mdb.DataVolumeName(), mdb.GetMongodConfiguration().GetDBDataDir(), statefulset.WithSubPath("data")),
statefulset.CreateVolumeMount(mdb.DataVolumeName(), automationconfig.DefaultAgentLogPath, statefulset.WithSubPath("logs")),
}
mongodbAgentVolumeMounts = append(mongodbAgentVolumeMounts, mounts...)
mongodVolumeMounts = append(mongodVolumeMounts, mounts...)
singleModeVolumeClaim = statefulset.WithVolumeClaim(mdb.DataVolumeName(), dataPvc(mdb.DataVolumeName()))
if !isArbiter {
buildVolumesForMembers(mdb, &dataVolumeClaim, &logVolumeClaim, &singleModeVolumeClaim, &mongodbAgentVolumeMounts, &mongodVolumeMounts)
}

podSecurityContext, _ := podtemplatespec.WithDefaultSecurityContextsModifications()
Expand Down Expand Up @@ -537,3 +524,25 @@ func collectEnvVars() []corev1.EnvVar {

return envVars
}

// buildVolumesForMembers creates volume configurations for regular MongoDB data members
// These members need persistent storage for data and logs
func buildVolumesForMembers(mdb MongoDBStatefulSetOwner, dataVolumeClaim *statefulset.Modification, logVolumeClaim *statefulset.Modification, singleModeVolumeClaim *func(s *appsv1.StatefulSet), mongodbAgentVolumeMounts *[]corev1.VolumeMount, mongodVolumeMounts *[]corev1.VolumeMount) {

if mdb.HasSeparateDataAndLogsVolumes() {
logVolumeMount := statefulset.CreateVolumeMount(mdb.LogsVolumeName(), automationconfig.DefaultAgentLogPath)
dataVolumeMount := statefulset.CreateVolumeMount(mdb.DataVolumeName(), mdb.GetMongodConfiguration().GetDBDataDir())
*dataVolumeClaim = statefulset.WithVolumeClaim(mdb.DataVolumeName(), dataPvc(mdb.DataVolumeName()))
*logVolumeClaim = statefulset.WithVolumeClaim(mdb.LogsVolumeName(), logsPvc(mdb.LogsVolumeName()))
*mongodbAgentVolumeMounts = append(*mongodbAgentVolumeMounts, dataVolumeMount, logVolumeMount)
*mongodVolumeMounts = append(*mongodVolumeMounts, dataVolumeMount, logVolumeMount)
} else {
mounts := []corev1.VolumeMount{
statefulset.CreateVolumeMount(mdb.DataVolumeName(), mdb.GetMongodConfiguration().GetDBDataDir(), statefulset.WithSubPath("data")),
statefulset.CreateVolumeMount(mdb.DataVolumeName(), automationconfig.DefaultAgentLogPath, statefulset.WithSubPath("logs")),
}
*mongodbAgentVolumeMounts = append(*mongodbAgentVolumeMounts, mounts...)
*mongodVolumeMounts = append(*mongodVolumeMounts, mounts...)

}
}
28 changes: 19 additions & 9 deletions mongodb-community-operator/controllers/replica_set_controller.go
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Expand Up @@ -505,9 +505,10 @@ func (r *ReplicaSetReconciler) createOrUpdateStatefulSet(ctx context.Context, md
}

mongodbImage := getMongoDBImage(r.mongodbRepoUrl, r.mongodbImage, r.mongodbImageType, mdb.GetMongoDBVersion())
buildStatefulSetModificationFunction(mdb, mongodbImage, r.agentImage, r.versionUpgradeHookImage, r.readinessProbeImage)(&set)
if isArbiter {
buildArbitersModificationFunction(mdb)(&set)
buildArbitersModificationFunction(mdb, mongodbImage, r.agentImage, r.versionUpgradeHookImage, r.readinessProbeImage)(&set)
} else {
buildMembersModificationFunction(mdb, mongodbImage, r.agentImage, r.versionUpgradeHookImage, r.readinessProbeImage)(&set)
}

if _, err = statefulset.CreateOrUpdate(ctx, r.client, set); err != nil {
Expand Down Expand Up @@ -789,10 +790,10 @@ func getMongodConfigSearchModification(search *searchv1.MongoDBSearch) automatio
}
}

// buildStatefulSetModificationFunction takes a MongoDB resource and converts it into
// the corresponding stateful set
func buildStatefulSetModificationFunction(mdb mdbv1.MongoDBCommunity, mongodbImage, agentImage, versionUpgradeHookImage, readinessProbeImage string) statefulset.Modification {
commonModification := construct.BuildMongoDBReplicaSetStatefulSetModificationFunction(&mdb, &mdb, mongodbImage, agentImage, versionUpgradeHookImage, readinessProbeImage, true, "")
// buildBaseStatefulSetModificationFunction takes a MongoDB resource and creates statfulset base
// the tatfulset base.
func buildBaseStatefulSetModificationFunction(mdb mdbv1.MongoDBCommunity, mongodbImage, agentImage, versionUpgradeHookImage, readinessProbeImage string, isArbiter bool) statefulset.Modification {
commonModification := construct.BuildMongoDBReplicaSetStatefulSetModificationFunction(&mdb, &mdb, mongodbImage, agentImage, versionUpgradeHookImage, readinessProbeImage, true, "", isArbiter)
return statefulset.Apply(
commonModification,
statefulset.WithOwnerReference(mdb.GetOwnerReferences()),
Expand All @@ -803,17 +804,26 @@ func buildStatefulSetModificationFunction(mdb mdbv1.MongoDBCommunity, mongodbIma
buildAgentX509(mdb),
),
),

statefulset.WithCustomSpecs(mdb.Spec.StatefulSetConfiguration.SpecWrapper.Spec),
statefulset.WithObjectMetadata(
mdb.Spec.StatefulSetConfiguration.MetadataWrapper.Labels,
mdb.Spec.StatefulSetConfiguration.MetadataWrapper.Annotations,
),
)
}

func buildArbitersModificationFunction(mdb mdbv1.MongoDBCommunity) statefulset.Modification {
func buildMembersModificationFunction(mdb mdbv1.MongoDBCommunity, mongodbImage, agentImage, versionUpgradeHookImage, readinessProbeImage string) statefulset.Modification {
commonModification := buildBaseStatefulSetModificationFunction(mdb, mongodbImage, agentImage, versionUpgradeHookImage, readinessProbeImage, false)
return statefulset.Apply(
commonModification,
statefulset.WithCustomSpecs(mdb.Spec.StatefulSetConfiguration.SpecWrapper.Spec),
)
}

func buildArbitersModificationFunction(mdb mdbv1.MongoDBCommunity, mongodbImage, agentImage, versionUpgradeHookImage, readinessProbeImage string) statefulset.Modification {
commonModification := buildBaseStatefulSetModificationFunction(mdb, mongodbImage, agentImage, versionUpgradeHookImage, readinessProbeImage, true)

return statefulset.Apply(
commonModification,
statefulset.WithReplicas(mdb.StatefulSetArbitersThisReconciliation()),
statefulset.WithServiceName(mdb.ServiceName()),
statefulset.WithName(mdb.ArbiterNamespacedName().Name),
Expand Down
6 changes: 3 additions & 3 deletions mongodb-community-operator/controllers/replicaset_controller_test.go
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Expand Up @@ -357,15 +357,15 @@ func TestBuildStatefulSet_ConfiguresUpdateStrategyCorrectly(t *testing.T) {
mdb.Spec.Version = "4.0.0"
mdb.Annotations[annotations.LastAppliedMongoDBVersion] = "4.0.0"
sts := appsv1.StatefulSet{}
buildStatefulSetModificationFunction(mdb, "fake-mongodbImage", AgentImage, "fake-versionUpgradeHookImage", "fake-readinessProbeImage")(&sts)
buildBaseStatefulSetModificationFunction(mdb, "fake-mongodbImage", AgentImage, "fake-versionUpgradeHookImage", "fake-readinessProbeImage", false)(&sts)
assert.Equal(t, appsv1.RollingUpdateStatefulSetStrategyType, sts.Spec.UpdateStrategy.Type)
})
t.Run("On No Version Change, First Version", func(t *testing.T) {
mdb := newTestReplicaSet()
mdb.Spec.Version = "4.0.0"
delete(mdb.Annotations, annotations.LastAppliedMongoDBVersion)
sts := appsv1.StatefulSet{}
buildStatefulSetModificationFunction(mdb, "fake-mongodbImage", AgentImage, "fake-versionUpgradeHookImage", "fake-readinessProbeImage")(&sts)
buildBaseStatefulSetModificationFunction(mdb, "fake-mongodbImage", AgentImage, "fake-versionUpgradeHookImage", "fake-readinessProbeImage", false)(&sts)
assert.Equal(t, appsv1.RollingUpdateStatefulSetStrategyType, sts.Spec.UpdateStrategy.Type)
})
t.Run("On Version Change", func(t *testing.T) {
Expand All @@ -382,7 +382,7 @@ func TestBuildStatefulSet_ConfiguresUpdateStrategyCorrectly(t *testing.T) {

mdb.Annotations[annotations.LastAppliedMongoDBVersion] = string(bytes)
sts := appsv1.StatefulSet{}
buildStatefulSetModificationFunction(mdb, "fake-mongodbImage", AgentImage, "fake-versionUpgradeHookImage", "fake-readinessProbeImage")(&sts)
buildBaseStatefulSetModificationFunction(mdb, "fake-mongodbImage", AgentImage, "fake-versionUpgradeHookImage", "fake-readinessProbeImage", false)(&sts)
assert.Equal(t, appsv1.OnDeleteStatefulSetStrategyType, sts.Spec.UpdateStrategy.Type)
})
}
Expand Down