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Distinct Property supports arbitrary limit

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This PR enhances the distinct_property constraint such that a limit can
be specified in the RTarget/value parameter. This allows constraints
such as:

```
constraint {
  distinct_property = "${meta.rack}"
  value = "2"
}
```

This restricts any given rack from running more than 2 allocations from
the task group.

Fixes https://github.com/hashicorp/nomad/issues/1146
This commit is contained in:
Alex Dadgar
2017-07-31 16:44:17 -07:00
parent abdb7c3297
commit 4e71ba2e71
8 changed files with 506 additions and 66 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
website/source/api/json-jobs.html.md
View File

@@ -537,7 +537,9 @@ The `Constraint` object supports the following keys:
omitted.
- `distinct_property` - If set, the scheduler selects nodes that have a
distinct value of the specified property for each allocation. This can
distinct value of the specified property. The `RTarget` specifies how
many allocations are allowed to share the value of a property. The
`RTarget` must be 1 or greater and if omitted, defaults to 1. This can
be specified as a job constraint which applies the constraint to all
task groups in the job, or as a task group constraint which scopes the
effect to just that group. The constraint may not be specified at the

24
website/source/docs/job-specification/constraint.html.md
View File

@@ -75,6 +75,8 @@ all groups (and tasks) in the job.
>=
<
<=
distinct_hosts
distinct_property
regexp
set_contains
version
@@ -124,16 +126,18 @@ constraint {
```
- `"distinct_property"` - Instructs the scheduler to select nodes that have a
distinct value of the specified property for each allocation. When specified
as a job constraint, it applies to all groups in the job. When specified as a
group constraint, the effect is constrained to that group. This constraint can
not be specified at the task level. Note that the `value` parameter should be
omitted when using this constraint.
distinct value of the specified property. The `value` parameter specifies how
many allocations are allowed to share the value of a property. The `value`
must be 1 or greater and if omitted, defaults to 1. When specified as a job
constraint, it applies to all groups in the job. When specified as a group
constraint, the effect is constrained to that group. This constraint can not
be specified at the task level.
```hcl
constraint {
operator = "distinct_property"
attribute = "${meta.rack}"
value = "3"
}
```
@@ -142,7 +146,8 @@ constraint {
```hcl
constraint {
distinct_property = "${meta.rack}"
distinct_property = "${meta.rack}"
value = "3"
}
```
@@ -209,13 +214,14 @@ constraint {
A potential use case of the `distinct_property` constraint is to spread a
service with `count > 1` across racks to minimize correlated failure. Nodes can
be annotated with which rack they are on using [client
metadata][client-metadata] with values
such as "rack-12-1", "rack-12-2", etc. The following constraint would then
assure no two instances of the task group existed on the same rack.
metadata][client-metadata] with values such as "rack-12-1", "rack-12-2", etc.
The following constraint would assure that an individual rack is not running
more than 2 instances of the task group.
```hcl
constraint {
distinct_property = "${meta.rack}"
value = "2"
}
```