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revise with per crossplane#203
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zzxwill committed Sep 10, 2020
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34 changes: 13 additions & 21 deletions design/workload-labeling.md
Original file line number Diff line number Diff line change
Expand Up @@ -145,7 +145,7 @@ and pods.

## Proposal

Step 1: Setting the label `definition.oam.dev/unique-pod` as the unique identifier of pods
Step 1: Setting `spec.revisionLabel` as the unique identifier of pods

We found that if our final target workload resource is pod, we can always assume the pod has unique labels:

Expand All @@ -168,18 +168,14 @@ metadata:
controller-revision-hash: b8d6c88f6
```

Declare `definition.oam.dev/unique-pod` in WorkloadDefinition as OAM specified labels, which will always exist in pods.
Then trait automatically fills correlation fields by detecting the unique pod label, for example, generating service, split traffic, etc.
By Declaring `spec.revisionLabel` in WorkloadDefinition as OAM specified specification, of which the value will always exist
in pods, trait automatically fills correlation fields by detecting `revisionLabel`, for example, generating service, split traffic, etc.

```yaml
apiVersion: core.oam.dev/v1alpha2
kind: WorkloadDefinition
metadata:
name: xxx
labels:
definition.oam.dev/unique-pod: pod-template-hash # optional but recommended, values in [pod-template-hash, controller-revision-hash]
spec:
...
revisionLabel: pod-template-hash # optional but recommended, values in [pod-template-hash, controller-revision-hash]
```

Step 2: Utilizing generated workload labels to establish clear relationship between workloads and its component
Expand All @@ -197,7 +193,8 @@ metadata:
app.oam.dev/component: label-component
app.oam.dev/name: label-appconfig
app.oam.dev/revision: label-component-v1
definition.oam.dev/unique-pod: pod-template-hash
spec:
revisionLabel: pod-template-hash
```

Label `app.oam.dev/component` marks the Component, `app.oam.dev/name` marks the ApplicationConfiguration, and `app.oam.dev/revision`
Expand All @@ -214,22 +211,17 @@ spec:
name: label-nginx
```

Moreover, with recommended label `definition.oam.dev/unique-pod` in Component manifest set, we can see it is
generated as one label of the Deployment workload, which can help identify the pods.
Moreover, with recommended `spec.revisionLabel` set in Component manifest, we can see it is generated in `spec` field of
the Deployment workload, which can help identify the pods.

## Best practice

- For OAM users

We recommend you to set label `definition.oam.dev/unique-pod` in WorkloadDefinition and Component.

We do NOT recommend you to use Ingress/Service, HPA trait at all. Though based on the mechanism of this proposal,
we can automatically set the required, we encourage users to use official Route and Scale trait.

- For Trait builder
We recommend platform builders to set `spec.revisionLabel` in WorkloadDefinition, application developers to set
`spec.revisionLabel` in Component. Using Ingress/Service, or HPA trait is not recommended at all. Though based on the mechanism
of this proposal, we can automatically set the required, we encourage users to use official Route and Scale trait.

We recommend you to utilize those Workload labels to help identify the Components, ApplicationConfiguration and Pods, to
help implement operation logic.
We also recommend platform builders to utilize those Workload labels and `spec.revisionLabel` to help identify the Components
ApplicationConfiguration and Pods, to help implement operation logic.

## Impact to existing system

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