4.3. StatefulSets

Overview

The StatefulSets page manages every StatefulSet held on the MCM control plane in one place. A StatefulSet is the workload for applications that need to keep state; it provides a fixed network identity and persistent storage.

What it is for:

• Managing multi-cluster StatefulSets together
• Deploying and scaling stateful applications
• Guaranteeing pod order and uniqueness
• Checking the PropagationPolicy and OverridePolicy

Where StatefulSets are used:

• Databases (MySQL, PostgreSQL, MongoDB, and so on)
• Message queues (Kafka, RabbitMQ, and so on)
• Distributed storage (Cassandra, Elasticsearch, and so on)
• Applications that need to keep state

How the Screen Is Laid Out

The StatefulSets page shows the StatefulSet list as a table.

The Elements at the Top of the Page

Element	Description
Namespace filter	Shows only the StatefulSets of a particular namespace
Refresh button	Refreshes the StatefulSet list
Create button	Opens the dialog for creating a new StatefulSet
Search box	Searches by StatefulSet name

Table Columns

Column	Description	Sortable
Name	The StatefulSet name	✅
Namespace	The namespace the StatefulSet belongs to	✅
Status	Ready pods / desired pods	✅
Image	The container image name	✅
Age	The time since the StatefulSet was created	✅
Actions	The edit and delete buttons	-

How Status Is Shown

The Status column is shown as ready / desired:

• 2/2: both replicas are Ready
• 1/2: only 1 of 2 replicas is Ready

StatefulSet Detail

Clicking a StatefulSet row opens the detail panel.

The Detail Panel Header

Element	Description
StatefulSet name	The name of the chosen StatefulSet
Namespace	The namespace the StatefulSet belongs to
Sync Status	The N/N pod-ready figure

The Action Buttons

Button	What it does
Scale Down	Lowers the replica count
Scale Up	Raises the replica count
Restart	Rolling-restarts the StatefulSet
Refresh	Refreshes the StatefulSet information
Edit	Opens the YAML edit mode
Delete	Deletes the StatefulSet

The Tabs

The Overview Tab

Shows the StatefulSet's basic information, replica state, and the settings particular to a StatefulSet.

Basic information:

Item	Description
Name	The StatefulSet name
Namespace	The namespace the StatefulSet belongs to
Status	N/N ready
Age	The time since creation
Created	When the StatefulSet was created

Replica state:

Item	Description
Pod ready state	N / N pods ready (with a progress bar)
Desired Replicas	The replica count that is set
Ready Replicas	The number of replicas that are Ready
Current Replicas	The number of replicas running now
Updated Replicas	The number of replicas updated to the latest version

Pod state:

The pod state section shows the StatefulSet's pods visually:

• Running: pods working normally
• Pending: pods waiting to be scheduled
• Failed: pods that failed

StatefulSet Info:

Shows the settings particular to a StatefulSet:

Item	Description
Service Name	The headless service name (which provides the stable network identity)
Pod Management Policy	OrderedReady or Parallel
Update Strategy	RollingUpdate or OnDelete

Container images:

Shows the list of container images defined on the StatefulSet.

The Multi-Cluster Policies Tab

Shows the multi-cluster policies that apply to the StatefulSet.

PropagationPolicy:

Column	Description
Name	The PropagationPolicy name
Namespace	The namespace the policy belongs to
Scope	Namespace-scoped policies / cluster-scoped policies
Target Clusters	The list of target clusters

OverridePolicy:

Shown where there are per-cluster custom settings.

The Labels Tab

Shows the list of Kubernetes labels applied to the StatefulSet.

The Annotations Tab

Shows the list of annotations applied to the StatefulSet.

The Pods Tab

Shows the list of pods running for that StatefulSet.

Column	Description
Name	The pod name (my-statefulset-0, my-statefulset-1, for example)
Cluster	The cluster the pod is running on
Status	The pod state (Running / Pending / Failed and so on)
Node	The node the pod is scheduled on
Restarts	The pod restart count
Age	The time since the pod was created
Actions	The view and delete buttons

Note: StatefulSet pods carry sequential names (my-statefulset-0, my-statefulset-1, for example). Pods of the same name are created on each cluster.

The Events Tab

Shows the Kubernetes events related to the StatefulSet.

Creating a StatefulSet

Creates a new StatefulSet on the MCM control plane.

Fields

Field	Required	Description
Name	✅	The StatefulSet name
Namespace	✅	The namespace to deploy into
Service Name	✅	The headless service name
Replicas	✅	The initial replica count (default: 1)
Container image	✅	The container image URL
Volume claim template	-	The PersistentVolumeClaim template
Ports	-	The container port settings
Environment variables	-	The container environment variables

Editing the YAML

The "Edit YAML" tab lets you write the StatefulSet definition directly.

StatefulSet Operations

Scaling Up and Down

Adjusts the StatefulSet's replica count.

1. Choose the StatefulSet
2. Press the scale up (▲) or scale down (▼) button
3. The replica count rises or falls

Note: StatefulSet scaling happens in order:

• Scaling up: pods are created in the order 0, 1, 2...
• Scaling down: pods are deleted in reverse, ...2, 1, 0

Rolling Restart

Restarts every pod of the StatefulSet in turn.

1. Choose the StatefulSet
2. Press the "Restart" button in the detail panel
3. Press the "Restart" button in the confirmation dialog

The restart proceeds in reverse (from the last pod to the first).

Editing a StatefulSet

1. Choose the StatefulSet
2. Press the "Edit" button in the detail panel
3. Change the StatefulSet definition in the YAML editor
4. Press the "Save" button

Deleting a StatefulSet

⚠️ Caution: deleting a StatefulSet does not delete its PersistentVolumeClaims automatically. The PVCs have to be managed separately to preserve the data.

1. Choose the StatefulSet to delete
2. Press the "Delete" button in the detail panel
3. Type the StatefulSet name in the confirmation dialog
4. Press the "Delete" button

Worked Examples

Scenario 1: Deploying a Database Across Clusters

1. Press the "Create" button
2. Enter the StatefulSet details:
   • Name: mysql
   • Namespace: database
   • Service Name: mysql-headless
   • Replicas: 3
   • Container image: mysql:8.0
3. Set the volume claim template:
   • Storage class: standard
   • Capacity: 10Gi
4. Press the "Create" button
5. Name the target clusters with a PropagationPolicy

Scenario 2: Checking StatefulSet Status

1. Click the StatefulSet you want to check in the list
2. Check the replica state on the Overview tab
3. Check the service name and management policy in StatefulSet Info
4. Check the pod distribution per cluster on the Pods tab
5. Confirm the pod names are sequential (my-statefulset-0, my-statefulset-1)

Scenario 3: Scaling Out

1. Choose the StatefulSet to scale out
2. Press the "Scale Up" button
3. Watch the new pod being created in order (my-statefulset-2, for example)
4. The next pod is created only after that one becomes Ready

Scenario 4: A Rolling Update

1. Choose the StatefulSet and press "Edit"
2. Change the container image version (mysql:8.0 → mysql:8.1, for example)
3. Press "Save"
4. Watch the update proceed in reverse:
   • my-statefulset-2 → my-statefulset-1 → my-statefulset-0
5. Each pod updates only after the previous one becomes Ready

Scenario 5: Checking the Pods per Cluster

1. Choose the StatefulSet
2. Click the "Pods" tab
3. Check the pod of the same name on each cluster:
   • Cluster A: my-statefulset-0
   • Cluster B: my-statefulset-0
4. Check each pod's node, status, and restart count

Related Concepts

StatefulSet against Deployment

Trait	StatefulSet	Deployment
Pod name	Sequential and fixed (app-0, app-1)	Random (app-abc123)
Network identity	Stable (a headless service)	Dynamic
Storage	Persistent (the PVC is kept)	Ephemeral
Order	Creation and deletion order guaranteed	No order
Scaling	Sequential	Parallel
Where it is used	Databases, stateful apps	Stateless web apps

Pod Management Policies

OrderedReady (the default):

• Pods are created and deleted in order
• The next pod is created only after the previous one is Ready
• Suited to building a database cluster

Parallel:

• Every pod is created and deleted at once
• Used where order does not matter
• Used where fast scaling is needed

Update Strategies

RollingUpdate (the default):

• Updates the pods in reverse (last to first)
• partition: updates only the pods at or above a given index

OnDelete:

• A pod updates only when it is deleted by hand
• Used where complete control is needed

The Headless Service

A StatefulSet is used together with a headless service:

• A service whose ClusterIP is None
• It gives each pod its own DNS name
• For example mysql-0.mysql-headless.database.svc.cluster.local

Managing PersistentVolumeClaims

A StatefulSet's volume claim template:

• Creates its own PVC per pod
• The PVC is kept when the StatefulSet is deleted (preserving the data)
• The PVC has to be deleted by hand

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Next Steps

• Jobs -- managing multi-cluster Jobs
• CronJobs -- managing multi-cluster CronJobs
• PersistentVolumeClaims -- storage management

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