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Kustomize supports two patch strategies—JSON 6902 and Strategic Merge—to help you customize Kubernetes manifests. Use inline patches for quick edits or external patch files for better organization as your configuration grows.

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Patch Overview

Patch TypeOperation StyleInlineExternal File
JSON 6902 PatchJSON Patch RFC 6902 (add, remove, replace, etc.)✅✅
Strategic Merge PatchDeclarative field merge using Kubernetes’ native logic✅✅

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JSON 6902 Patches

JSON 6902 patches let you apply JSON-style operations to modify existing resources.

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1. Inline Definition

Embed the patch directly in your kustomization.yaml under patchesJson6902: 
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

resources:
  - deployment.yaml

patchesJson6902:
  - target:
      group: apps
      version: v1
      kind: Deployment
      name: api-deployment
    patch: |
      - op: replace
        path: /spec/replicas
        value: 5

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2. External File

Separate the patch into its own file (replica-patch.yaml) and reference it: kustomization.yaml 
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

resources:
  - deployment.yaml

patchesJson6902:
  - path: replica-patch.yaml
    target:
      group: apps
      version: v1
      kind: Deployment
      name: nginx-deployment
replica-patch.yaml 
- op: replace
  path: /spec/replicas
  value: 5
External JSON 6902 patches are ideal when you need to apply multiple operations or share patches across environments.

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Strategic Merge Patches

Strategic Merge Patches allow you to declaratively merge fields into existing resources.

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1. Inline Definition

Define the merge patch inline in kustomization.yaml under patchesStrategicMerge: 
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

resources:
  - deployment.yaml

patchesStrategicMerge:
  - |
    apiVersion: apps/v1
    kind: Deployment
    metadata:
      name: api-deployment
    spec:
      replicas: 5

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2. External File

Store the merge patch in a file (strategic-replica-patch.yaml) and reference it: kustomization.yaml 
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

resources:
  - deployment.yaml

patchesStrategicMerge:
  - strategic-replica-patch.yaml
strategic-replica-patch.yaml 
apiVersion: apps/v1
kind: Deployment
metadata:
  name: api-deployment
spec:
  replicas: 5
The metadata.name in your patch must exactly match the target resource name; otherwise, the patch won’t be applied.

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Best Practices

  • Use inline patches for small, one-off tweaks.
  • Move to external files when your patches multiply or you need reuse.
  • Group related patches in directories to manage environment overlays (e.g., overlays/staging, overlays/production).

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References

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