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devopscritical PriorityID: k8s-pod-disruption-budget-pdb

Kubernetes PodDisruptionBudget (PDB) & Zero-Downtime Node Draining Standard

Production Kubernetes reliability standard. Mandates configuring PodDisruptionBudget (PDB) with minAvailable or maxUnavailable for all replicated deployments, preventing involuntary cluster maintenance (node drains, cluster upgrades, spot terminations) from taking down services completely.

Prohibited Anti-Pattern: AI creates Kubernetes Deployments without PodDisruptionBudgets, allowing kubectl drain or node autoscaling to terminate all replicas simultaneously.

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---
description: Kubernetes PodDisruptionBudget (PDB) & Zero-Downtime Node Draining Standard - Production Kubernetes reliability standard. Mandates configuring PodDisruptionBudget (PDB) with minAvailable or maxUnavailable for all replicated deployments, preventing involuntary cluster maintenance (node drains, cluster upgrades, spot terminations) from taking down services completely.
globs: **/pdb*.yaml, **/deployment*.yaml, **/k8s/**/*.yaml
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/k8s-pod-disruption-budget-pdb"
---

# Kubernetes PodDisruptionBudget (PDB) & Zero-Downtime Node Draining Standard

> **Severity**: CRITICAL | **Category**: devops
> **Anti-Pattern Warning**: AI creates Kubernetes Deployments without PodDisruptionBudgets, allowing kubectl drain or node autoscaling to terminate all replicas simultaneously.

## System Constraints
You are a Kubernetes Reliability Engineer (SRE). NEVER deploy multi-replica production workloads without an accompanying PodDisruptionBudget (PDB). Without a PDB, routine node upgrades, autoscaler scale-downs, and maintenance drains will terminate 100% of pods at once, causing service outages.

## Strict Guidelines
- MUST define a PodDisruptionBudget for every Deployment having 2 or more replicas.
- MUST set either minAvailable: 1 (or 50%) or maxUnavailable: 1 to ensure service continuity during node drainage.
- MUST ensure matchLabels in the PDB match the pod template labels in the Deployment exactly.
- MUST NOT configure minAvailable: 100% on small deployments, which completely deadlocks node drain operations.
- SHOULD combine PDB with topologySpreadConstraints across availability zones.

## Bad vs Good Implementations
### Configuring PodDisruptionBudget for Resilient Node Drainage

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Without a PDB, the Kubernetes eviction API evicts all pods without waiting for replacements to achieve Ready state, causing an immediate 503 outage for end users.
```yaml
# FATAL: Deployment without PDB can be completely wiped out during node drain
apiVersion: apps/v1
kind: Deployment
metadata:
  name: api-service
spec:
  replicas: 3
  # Missing PodDisruptionBudget: If nodes drain, all 3 pods can be killed at once!
```

#### Production Standard (Correct)
> **Standard**: The PodDisruptionBudget protects the deployment by blocking eviction until new replacement pods are healthy, guaranteeing zero-downtime rolling node upgrades.
```yaml
apiVersion: policy/v1
kind: PodDisruptionBudget
metadata:
  name: api-service-pdb
  namespace: production
spec:
  minAvailable: 2 # Guarantees at least 2 pods remain online at all times
  selector:
    matchLabels:
      app: api-service
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: api-service
  namespace: production
spec:
  replicas: 3
  selector:
    matchLabels:
      app: api-service
  template:
    metadata:
      labels:
        app: api-service
    spec:
      containers:
      - name: web
        image: api-service:v2.1
```

Recommended MCP Servers (mcp-serverlist.com)

Equip agent with system tools to verify code for this stack.

Kubernetes PDB & Availability Auditor MCP

Scans Kubernetes clusters for multi-replica deployments missing PodDisruptionBudgets.

Recommended Agent Skills (askills.dev)

Ready-to-use executable skill functions tailored to this stack.

askills: Kubernetes PDB Generator

Generates policy/v1 PodDisruptionBudgets matched to Deployment replica counts.

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Kubernetes PodDisruptionBudget (PDB) & Zero-Downtime Node Draining Standard

Kubernetes PodDisruptionBudget (PDB) & Zero-Downtime Node Draining Standard defines an industrial-grade behavioral standard for devops engineering. Production Kubernetes reliability standard. Mandates configuring PodDisruptionBudget (PDB) with minAvailable or maxUnavailable for all replicated deployments, preventing involuntary cluster maintenance (node drains, cluster upgrades, spot terminations) from taking down services completely. Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: AI creates Kubernetes Deployments without PodDisruptionBudgets, allowing kubectl drain or node autoscaling to terminate all replicas simultaneously. Without an explicit system instruction file, developers spend hours debugging silent failures.

Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure Mode	AI Symptom (The Anti-Pattern)	Severity	Production Impact & Remedy
AI Hallucination & Deprecation Drift	AI creates Kubernetes Deployments without PodDisruptionBudgets, allowing kubectl drain or node autoscaling to terminate all replicas simultaneously.	Critical	Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production. Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture Inconsistency	AI assistants produce mixed paradigms across files, creating fragmented codebase conventions.	Medium	Increases cognitive load during code reviews and leads to maintenance debt across engineering teams. Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.

Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

1

MUST define a PodDisruptionBudget for every Deployment having 2 or more replicas.

MUST define a PodDisruptionBudget for every Deployment having 2 or more replicas.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.

Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.

2

MUST set either minAvailable

MUST set either minAvailable: 1 (or 50%) or maxUnavailable: 1 to ensure service continuity during node drainage.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.

Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.

3

MUST ensure matchLabels in the PDB match the pod template labels in the Deployment exactly.

MUST ensure matchLabels in the PDB match the pod template labels in the Deployment exactly.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.

Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.

4

MUST NOT configure minAvailable

MUST NOT configure minAvailable: 100% on small deployments, which completely deadlocks node drain operations.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.

Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.

5

SHOULD combine PDB with topologySpreadConstraints across availability zones.

SHOULD combine PDB with topologySpreadConstraints across availability zones.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.

Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.

Technical Questions & Answers

Frequently Asked Technical Questions

Common questions developers face when configuring AI coding assistants for this stack:

Q:Why is Kubernetes PodDisruptionBudget (PDB) & Zero-Downtime Node Draining Standard critical for AI coding assistants?

Production Kubernetes reliability standard. Mandates configuring PodDisruptionBudget (PDB) with minAvailable or maxUnavailable for all replicated deployments, preventing involuntary cluster maintenance (node drains, cluster upgrades, spot terminations) from taking down services completely. Without explicit behavioral boundaries, AI coding assistants (Cursor, Claude Code, Windsurf, Codex) rely on training data averages, which frequently produce deprecated, inefficient, or vulnerable code patterns.

Q:How does adopting this rule prevent AI hallucinations?

This rule explicitly declares what the AI must avoid (AI creates Kubernetes Deployments without PodDisruptionBudgets, allowing kubectl drain or node autoscaling to terminate all replicas simultaneously.) and prescribes verified positive examples. Grounding the LLM with negative and positive pairs eliminates guesswork.

Q:Which AI coding environments are supported?

This specification is multi-platform compatible: Cursor (.cursor/rules/*.mdc & .cursorrules), Anthropic Claude Code (CLAUDE.md), Windsurf (.windsurfrules), Codex / Cline (AGENTS.md), and GitHub Copilot (.github/copilot-instructions.md).

Q:Can I combine this rule with other technology stacks?

Yes. Use the Interactive Stack Builder or download an Agent Pack to merge this rule with other frontend, backend, database, security, and DevOps rules without syntax collision.

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