What are the key differences between StatefulSets and Deployments in Kubernetes, and when should each be used?

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Cluster information:

Kubernetes version:
Cloud being used: (put bare-metal if not on a public cloud)
Installation method:
Host OS:
CNI and version:
CRI and version:

What are the key differences between StatefulSets and Deployments in Kubernetes, and how do they impact the management of containerized applications? In what scenarios should you use StatefulSets over Deployments, particularly when dealing with stateful applications, persistent storage, and unique network identities? Additionally, how do these two resources affect scaling, updating, and rolling back pods in a Kubernetes cluster?

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If you care specifically for the identity of the pod you would want to go for statefulsets if the pod name is mysql-1 or kafka-1 and when pod restarts you want same name for the replacement pod because its attached to same storage, same traffic with dns name internally used or any other dependency on that process ideally good case for database services.

Pod:

  • Statefuleset - Same name (Identity) for pod.
  • Deployment - different name

Storage:

  • Statefuleset - It will get same storage, like pod restart will connect to same storage. If not handled correctly it can crease issues. Gets little complicated sometime depending on how you handle it.
  • Deployment - Doesn’t care about volume if it gets deleted and lose data. Ephemeral.

Network:

  • Statefuleset - same pod name, easy for network connections. It care about its identity.
  • Deployment - random name for pods/

Pod scheduling while coming up and roll back:

  • Statefuleset - Pod comes in defined manner.
  • Deployment - It doesn’t care which pod comes first or last.

Examples use cases:

  • Statefuleset - Databases, streaming services like kafka, distributed systems, cache systems
  • Deployment - Application codebase that has business logic, microservices, APIs
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