Deployments vs StatefulSets: When to Use Each in Kubernetes

One of the most common early questions in Kubernetes is:

Should I use a Deployment or a StatefulSet?

They look similar at first glance — both manage pods, replicas, and updates — but they are designed for very different types of workloads. Choosing the wrong one can lead to unnecessary complexity or broken applications.

This post breaks down what each controller is for, how they differ, and when you should use one over the other.

What Problem Do These Controllers Solve?

In Kubernetes, you rarely create pods directly.

Instead, you define a controller that:

• Creates pods
• Replaces them if they fail
• Scales them up or down
• Handles updates safely

Deployments and StatefulSets are two of the most common workload controllers — but they serve different purposes.

Deployments: Stateless, Scalable Workloads

A Deployment is the default choice for most applications.

What Deployments Are Good At

Deployments are designed for stateless workloads, where:

• Any pod can handle any request
• Pods are interchangeable
• Losing a pod does not lose data

Examples:

• Web frontends
• APIs
• Microservices
• Background workers

Key Characteristics of Deployments

• Pods are identical and interchangeable
• Pod names are randomized
  
  my-app-5f8d6b9d6f-x7k2m

• Pods can be created or destroyed in any order
• Rolling updates are simple and fast
• Scaling is trivial

If Kubernetes kills and recreates a pod, the application shouldn’t care.

Typical Deployment Use Case

apiVersion: apps/v1
kind: Deployment
spec:
  replicas: 3

apiVersion: apps/v1
kind: Deployment
spec:
  replicas: 3

You’re saying:

“I want three copies of this application running at all times.”

Which pod handles which request doesn’t matter.

StatefulSets: Identity and Order Matter

A StatefulSet is designed for stateful workloads, where identity, ordering, and persistence are important.

What StatefulSets Are Good At

StatefulSets are used when:

• Each pod needs a stable identity
• Each pod needs its own persistent storage
• Startup and shutdown order matters

Examples:

• Databases (PostgreSQL, MySQL, MongoDB)
• Distributed systems (Kafka, ZooKeeper, etcd)
• Applications with leader/follower roles

Key Characteristics of StatefulSets

• Pods have stable, predictable names

db-0
db-1
db-2

db-0
db-1
db-2

• Each pod keeps its identity across restarts
• Each pod typically gets its own PersistentVolume
• Pods are created and deleted in order
• Scaling is controlled and deliberate

If db-1 dies, Kubernetes recreates db-1, not a random replacement.

Typical StatefulSet Use Case

apiVersion: apps/v1
kind: StatefulSet
spec:
  replicas: 3

apiVersion: apps/v1
kind: StatefulSet
spec:
  replicas: 3

But unlike a Deployment:

• db-0, db-1, and db-2 are distinct
• Each has its own storage and network identity

The Core Differences (Side by Side)

Storage: The Deciding Factor

If your application:

• Does not require persistent storage → Deployment
• Requires unique, durable storage per instance → StatefulSet

StatefulSets commonly use:

• VolumeClaimTemplates
• One PersistentVolume per replica

Deployments can use storage, but:

• All replicas usually share it
• Identity is not preserved

Networking Differences

Deployments typically sit behind:

• A Service that load-balances traffic

StatefulSets often use:

• A Headless Service
• Direct pod-to-pod communication
• Stable DNS names like:

db-0.db.default.svc.cluster.local

db-0.db.default.svc.cluster.local

This is critical for clustered systems.

Common Mistakes

❌ Using StatefulSets for Stateless Apps

This adds:

• Unnecessary complexity
• Slower scaling
• Harder updates

If you don’t need stable identity or storage — don’t use it.

❌ Using Deployments for Databases

This often leads to:

• Data loss
• Split-brain scenarios
• Hard-to-debug failures

Databases expect identity and stability.

How This Plays Out in OpenShift

OpenShift supports both controllers fully, but adds:

• Better storage integration
• Operator-based patterns for stateful apps
• Safer defaults for updates and security

In production OpenShift environments:

• Deployments dominate application workloads
• StatefulSets are used carefully and intentionally
• Many databases are deployed via Operators, which internally manage StatefulSets

Understanding StatefulSets helps you understand what Operators are doing under the hood.

Rule of Thumb

If you remember nothing else, remember this:

• Stateless app? → Deployment
• Needs identity or per-pod storage? → StatefulSet

When in doubt:

• Start with a Deployment
• Move to a StatefulSet only when requirements force you

What’s Next?

Future posts will cover:

• Deployments vs DaemonSets
• StatefulSets and storage classes
• Operators vs raw Kubernetes controllers
• Running databases safely on OpenShift

Final Thoughts

Deployments and StatefulSets solve different problems — neither is “better” than the other.

The key is understanding your application’s needs and choosing the controller that matches them.

Make Kubernetes work for you, not against you.