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syscod3 merged 1 commit into from
Sep 26, 2026
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docs(unraid): record workload placement policy #123

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48 changes: 48 additions & 0 deletions clusters/unraid-lab/README.md
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Expand Up @@ -57,3 +57,51 @@ Harbor API) provisions:
> v1.1 (cross-project): mint the robot credentials on demand from
> [tessera](https://github.com/syscode-labs/tessera) (a Harbor create-then-delete
> Source) instead of static robots.

## Workload placement

### The rule

The Imp node is reserved for Imp. Only Imp workloads, DaemonSets, and a short
approved list of low-demand workloads may run there. Other workloads must not
tolerate `imp.dev/runner:NoSchedule`.

Normal workloads are spread across the two general-purpose control-plane nodes.
This is deliberate: putting every workload on every node would defeat the Imp
reservation.

### Capacity budget

Use resource **requests** as the scheduler budget. Actual use is monitored
separately.

| Node class | CPU budget | Memory budget | Why |
| --- | ---: | ---: | --- |
| General-purpose control plane | 2.655 CPU (90%) | 85% of allocatable memory | Keep room for Talos and Kubernetes. |
| Imp node | 1.95 CPU | 3.96 GiB | Reserve 1 CPU and 2.2 GiB for an on-demand ImpVM. |

The Imp memory reservation is 110% of a 2 GiB VM: 2.2 GiB.

### How this will be enforced

1. Keep the existing Imp taint. Normal workloads do not tolerate it.
2. Give ImpVMs a higher priority than the reserve workload.
3. Place a preemptible reserve workload on the Imp node that requests 1 CPU and
2.2 GiB. The scheduler then keeps that space available until an ImpVM needs
it.
4. Add topology-spread rules to eligible low-demand workloads so replicas prefer
different general-purpose nodes.
5. Require CPU and memory requests for every workload managed for this cluster.

This is a target policy, not a live guarantee yet. Do not change placement until
all healthy members, live usage, requests, and the rendered workload rules have
been checked.

### Before any placement change

- Confirm Omni's healthy-member count, not only Kubernetes `Ready`.
- Confirm each eligible node has no memory, disk, or process pressure.
- Check actual CPU and memory use plus requested capacity.
- Render every changed workload.
- Verify after reconciliation that no non-Imp workload has the Imp toleration or
lands on the Imp node.
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