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Add Coordinator concept #702

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Nov 8, 2024
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Add Coordinator concept #702

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9cfde5e
Add Coordinator concept
avrittrohwer Nov 8, 2024
242ac89
Add example label value
avrittrohwer Nov 8, 2024
60d774d
Fix indentation
avrittrohwer Nov 8, 2024
1f4e44d
Add kueue fixed v0.8 version
avrittrohwer Nov 8, 2024
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45 changes: 45 additions & 0 deletions site/content/en/docs/concepts/_index.md
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Expand Up @@ -125,6 +125,51 @@ NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
pytorch-workers ClusterIP None <none> <none> 25m
```

### Coordinator

A specific pod can be assigned as coordinator using `spec.coordinator`. If defined, a `jobset.sigs.k8s.io/coordinator`
annotation and label with the the stable network endpoint of the coordinator pod will be added to all Jobs and pods in the JobSet.
This label can be useful by other pods. For example:

```yaml
apiVersion: jobset.x-k8s.io/v1alpha2
kind: JobSet
metadata:
name: pytorch
spec:
coordinator:
replicatedJob: leader
jobIndex: 0
podIndex: 0
replicatedJobs:
- name: leader
replicas: 1
template:
spec:
parallelism: 1
completions: 1
...
- name: workers
replicas: 1
template:
spec:
parallelism: 8
completions: 8
template:
spec:
containers:
- name: worker
env:
- name: LEADER_ADDRESS
valueFrom:
fieldRef:
fieldPath: "metadata.labels['jobset.sigs.k8s.io/coordinator']"
...
```

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For completeness, can we include an example of the resulting label/annotation that would be applied to jobs/pods, for the example spec above? So the user can verify correctness and understand what they should expect the stable network endpoint to look like.

i.e., jobset.sigs.k8s.io/coordinator=pytorch-leader-0-0.pytorch

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Added!

WARNING: if using Kueue with JobSet, ensure Kueue version v0.9.0+ is installed. Prior versions are built using a JobSet api definition that does
not have the coordinator field: https://github.com/kubernetes-sigs/jobset/issues/701.

### Exclusive Job to topology placement

The JobSet annotation `alpha.jobset.sigs.k8s.io/exclusive-topology` defines 1:1 job to topology placement.
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