Cluster operators want to have better control over memory
oversubscription and may want to enable/disable it based on their
experience.
This PR adds a scheduler configuration field to control memory
oversubscription. It's additional field that can be set in the [API via Scheduler Config](https://www.nomadproject.io/api-docs/operator/scheduler), or [the agent server config](https://www.nomadproject.io/docs/configuration/server#configuring-scheduler-config).
I opted to have the memory oversubscription be an opt-in, but happy to change it. To enable it, operators should call the API with:
```json
{
"MemoryOversubscriptionEnabled": true
}
```
If memory oversubscription is disabled, submitting jobs specifying `memory_max` will get a "Memory oversubscription is not
enabled" warnings, but the jobs will be accepted without them accessing
the additional memory.
The warning message is like:
```
$ nomad job run /tmp/j
Job Warnings:
1 warning(s):
* Memory oversubscription is not enabled; Task cache.redis memory_max value will be ignored
==> Monitoring evaluation "7c444157"
Evaluation triggered by job "example"
==> Monitoring evaluation "7c444157"
Evaluation within deployment: "9d826f13"
Allocation "aa5c3cad" created: node "9272088e", group "cache"
Evaluation status changed: "pending" -> "complete"
==> Evaluation "7c444157" finished with status "complete"
# then you can examine the Alloc AllocatedResources to validate whether the task is allowed to exceed memory:
$ nomad alloc status -json aa5c3cad | jq '.AllocatedResources.Tasks["redis"].Memory'
{
"MemoryMB": 256,
"MemoryMaxMB": 0
}
```
Start tracking a new MemoryMaxMB field that represents the maximum memory a task
may use in the client. This allows tasks to specify a memory reservation (to be
used by scheduler when placing the task) but use excess memory used on the
client if the client has any.
This commit adds the server tracking for the value, and ensures that allocations
AllocatedResource fields include the value.
* ar: support opting into binding host ports to default network IP
* fix config plumbing
* plumb node address into network resource
* struct: only handle network resource upgrade path once
We currently log an error if preemption is unable to find a suitable set of
allocations to preempt. This commit changes that to debug level since not finding
preemptable allocations is not an error condition.
This adds constraints for asserting that a given attribute or value
exists, or does not exist. This acts as a companion to =, or !=
operators, e.g:
```hcl
constraint {
attribute = "${attrs.type}"
operator = "!="
value = "database"
}
constraint {
attribute = "${attrs.type}"
operator = "is_set"
}
```
Also changes the logic for score when there is more than one task
requesting a device. Since inter task affinities are already normalized,
we take the average of the scores across tasks.
This commit implements an allocation selection algorithm for finding
allocations to preempt. It currently special cases network resource asks
from others (cpu/memory/disk/iops).
