Nomad v1.2.6 has problem described below, while Nomad v 1.1.5 works as expected.
Possibly related:
Expected
The setup is a set of nodes with ${node.class} = worker and a few other nodes in the cluster. All the worker nodes should run the worker task, all other nodes should not. So a a job with type = "system" is used, and the following constraint is added to the worker group:
constraint {
attribute = "${node.class}"
operator = "="
value = "worker"
}
Observed
This works sometimes, in particular when there are no allocations on the cluster. But running nomad job plan after allocations are running displays the following warning:
Scheduler dry-run:
- WARNING: Failed to place allocations on all nodes.
Task Group "worker" (failed to place 1 allocation):
* Class "entry": 1 nodes excluded by filter
* Constraint "${node.class} = worker": 1 nodes excluded by filter
This should not be a warning, as the allocations match the job definition, considering the constraints.
nomad job run produces the desired state and the job state is displayed as “not scheduled” on all non-worker nodes.
Removing the constrains shows no warning, but obviously schedules the worker task on non-worker nodes, which is unwanted.
The only workaround seems be to ignore warnings, which defeats the purpose of nomad job plan, or create a entire separate cluster for the workers.