open-nomad/website/pages/docs/autoscaling/policy.mdx

---
layout: docs
page_title: Scaling Policies
sidebar_title: Policy
description: >
  Scaling policies describe the target resource desired state and how to
  perform calculations to ensure the current state reaches the desired.
---

# Nomad Autoscaler Scaling Policies

Nomad Autoscaler scaling policies can be configured via the
[task group `scaling` stanza][jobspec_scaling_stanza] or by configuration
files stored on disk.

## Top Level Options

- `enabled` - A boolean flag that allows operators to administratively disable a
  policy from active evaluation.

- `min` - The minimum running count of the targeted resource. This can be 0 or any
  positive integer.

- `max` - The maximum running count of the targeted resource. This can be 0 or any
  positive integer.

## `policy` Options

- `cooldown` - A time interval after a scaling action during which no additional
  scaling will be performed on the resource. It should be provided as a duration
  (e.g.: `"5s"`, `"1m"`). If omitted the configuration value
  [policy_default_cooldown][policy_default_cooldown_agent] from the agent will
  be used.

- `evaluation_interval` - Defines how often the policy is evaluated by the
  Autoscaler. It should be provided as a duration (e.g.: `"5s"`, `"1m"`). If
  omitted the configuration value [default_evaluation_interval][eval_interval_agent]
  from the agent will be used.

- `target` - Defines where the autoscaling target is running. Detailed information
  on the configuration options can be found on the [Target Plugins][target_plugin_docs]
  page.

- `check` - Specifies one or more checks to be executed when determining if a
  scaling action is required.

## `check` Options

- `source` - The APM plugin that should handle the metric query. If omitted,
  this defaults to using the Nomad APM.

- `query` - The query to run against the specified APM. Currently this query
  should return a single value. Detailed information on the configuration options
  can be found on the [APM Plugins][apm_plugin_docs] page.

- `strategy` - The strategy to use, and it's configuration when calculating the
  desired state based on the current count and the metric returned by the APM.
  Detailed information on the configuration options can be found on the
  [Strategy Plugins][strategy_plugin_docs] page.

### Example

A full example of a policy document that can be written into the Nomad task group
`scaling` stanza or via a file within the `policy_dir` can be seen below.

```hcl
min     = 2
max     = 10
enabled = true

policy {
  evaluation_interval = "5s"
  cooldown            = "1m"

  target "target" {
    Job   = "example"
    Group = "example"
  }

  check "active_connections" {
    source = "prometheus"
    query  = "scalar(open_connections_example_cache)"

    strategy "target_value" {
      target = 10
    }
  }
}
```

[policy_default_cooldown_agent]: /docs/autoscaling/agent#default_cooldown
[eval_interval_agent]: /docs/autoscaling/agent#default_evaluation_interval
[target_plugin_docs]: /docs/autoscaling/plugins/target
[strategy_plugin_docs]: /docs/autoscaling/plugins/strategy
[apm_plugin_docs]: /docs/autoscaling/plugins/apm
[jobspec_scaling_stanza]: /docs/job-specification/scaling