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ECD Patch is meant to provide a flexible option for users to define and provision Kubernetes objects that suits their system architecture or to tailor the ECD to their preferred flavour.

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Strategic Merge Patch is a custom implementation of Merge Patch. For a detailed explanation of how it works and why it needed to be introduced, see API Conventions on Patch - Strategic Merge. In general, Strategic Merge Patch works better when it comes to merging K8S objects in a list. However, not all list can be merged, in detailed, please refer to object that comes with “Patch Strategy: Merge” in https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.18

Example below shows how to add a host alias to the deployment (pod), which will basically add an entry into /etc/hosts

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Basically, an ECD will resulting in creating different K8S objects, 1 of them is Deployment object. The rollout strategy is default to RollingUpdate, through ECD patch we can change it to other strategy such as Recreate. The change can be seen on the spec.strategy.type (deployment)on After ECD Patch.

apiVersion: mz.digitalroute.com/v1alpha1
kind: ECDeployment
metadata:
  name: ecd-test-rolling-strategy
spec:
  enabled: true
  patchType: "application/strategic-merge-patch+json"
  patch: |
    spec:
      strategy:
        type: Recreate
  image: dtr.digitalroute.com/dr/mz10:10.1.0.0-dev-20200813052033.a224284-ec
  workflows:
  - template: Default.http2
    instances:
      - name: server-1
        parameters: |
          {
            "port": 8989
          }

apiVersion: apps/v1
kind: Deployment
metadata:
  ...
  ...
spec:
  progressDeadlineSeconds: 600
  replicas: 1
  revisionHistoryLimit: 10
  selector:
    matchLabels:
      app: ecd-test-rolling-strategy
  strategy:
    type: Recreate
  template:
    ...
    ...

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