In Kubernetes, the resource version is a crucial concept used for optimistic concurrency control. Let me explain what it means:

1. Resource Version:

   • All Kubernetes resources have a field called resourceVersion as part of their metadata.

   • This resourceVersion is a string that uniquely identifies the internal version of an object.

   • Clients (such as controllers or other components) use this value to determine when objects have changed.

   • When an object is modified, its resourceVersion is updated.

   • You can think of it as a version number for the resource within the Kubernetes cluster.

2. Optimistic Concurrency:

   • Kubernetes leverages resource versions to achieve optimistic concurrency control.

   • When multiple clients (such as controllers or users) attempt to modify the same resource simultaneously, Kubernetes ensures that changes don’t conflict.

   • Clients read the current resourceVersion before making changes.

   • When updating the resource, they include the resourceVersion in the request.

   • If the current resourceVersion matches the one provided, the update proceeds.

   • Otherwise, the client receives a conflict error, indicating that someone else modified the resource in the meantime.

3. Use Cases:

   • Resource versions are essential for scenarios like rolling updates, where you want to avoid conflicts between concurrent updates.

   • They allow you to track changes and maintain consistency across the cluster.

Remember, the resourceVersion helps Kubernetes manage concurrent modifications and ensures data integrity within the system.