---
layout: docs
page_title: Agent
sidebar_title: Agent
description: The Nomad Autoscaler is a long lived process which coordinates scaling activates.
---

# Nomad Autoscaler Agent

The Nomad Autoscaler agent has a variety of parameters that can be specified
via configuration files or command-line flags. Configuration files are written
in [HCL][hcl_v2]. The Nomad Autoscaler can read and combine parameters from
multiple configuration files or directories to configure the agent.

## Nomad Namespaces

The Nomad Autoscaler currently has limited support for
[Nomad Namespaces][nomad_namespaces]. The `nomad` configuration below supports
specifying a namespace; if configured with a namespace, the Autoscaler will
retrieve scaling policies and perform autoscaling only for jobs in that
namespace. A future version will include support for multiple namespaces.

## Nomad ACLs

The Nomad Autoscaler can be configured to interact with an ACL-enabled Nomad
cluster. Nomad 0.11 includes the `scale` ACL policy disposition specifically for
supporting the operations of the Nomad Autoscaler. Therefore, the
following policy is sufficient for creating an ACL token that can be used by
the autoscaler for fetching scaling policies and scaling jobs:

```hcl
namespace "default" {
  policy = "scale"
}
```

Other APM and target plugins may require additional ACLs; see the plugin documentation for more information.

## Load Order and Merging

The Nomad Autoscaler agent supports multiple configuration files, which can be
provided using the [`-config`][autoscaler_cli_config] CLI flag. The flag can
accept either a file or folder. In the case of a folder, any `.hcl` and `.json`
files in the folder will be loaded and merged in lexicographical order. Directories
are not loaded recursively.

For example:

```shell-session
$ nomad-autoscaler agent -config=autoscaler.conf -config=/etc/nomad-autoscaler -config=extra.json
```

This will load configuration from `autoscaler.conf`, from `.hcl` and `.json` files
under `/etc/nomad-autoscaler`, and finally from `extra.json`. As each file is
processed, its contents are merged into the existing configuration. When merging,
any non-empty values from the latest config file will append or replace
parameters in the current configuration. An empty value means `""` for strings,
`0` for integer or float values, and `false` for booleans.

## SIGHUP Reload

The Nomad Autoscaler agent supports handling the `SIGHUP` signal for reloading without the need for
restarting the agent. When sending a `SIGHUP` signal to the agent process, the agent will perform the
following actions.

- reload the contents of the scaling policy directory as defined by the [`-policy-dir`][autoscaler_cli_policy_dir]
  parameter.

## General Parameters

- `log_level` `(string: "INFO")` - Specify the verbosity level of Nomad
  Autoscaler's logs. Valid values include DEBUG, INFO, and WARN, in decreasing
  order of verbosity.

- `log_json` `(bool: false)` - Output logs in a JSON format.

- `plugin_dir` `(string: "./plugins")` - The plugin directory is used to
  discover Nomad Autoscaler plugins.

## `http` Block

The `http` block configures the Nomad Autoscaler's HTTP endpoint.

```hcl
http {
  bind_address = "10.0.0.10"
  bind_port    = 9999
}
```

### `http` Parameters

- `bind_address` `(string: "127.0.0.1")` - The HTTP address that the server will
  bind to.

- `bind_port` `(int: 8080)` - The port that the server will bind to.

## `nomad` Block

The `nomad` block configures the Nomad Autoscaler's Nomad client.

```hcl
nomad {
  address = "http://my-nomad.systems:4646"
  region  = "esp-vlc-1"
}
```

### `nomad` Parameters

- `address` `(string: "http://127.0.0.1:4646")` - The address of the Nomad server
  in the form of `protocol://addr:port`.

- `region` `(string: "global")` - The region of the Nomad servers to connect with.

- `namespace` `(string: "")` - The target namespace for queries and actions bound
  to a namespace.

- `token` `(string: "")` - The SecretID of an ACL token to use to authenticate
  API requests with.

- `http_auth` `(string: "")` - The authentication information to use when connecting
  to a Nomad API which is using HTTP authentication.

- `ca_cert` `(string: "")` - Path to a PEM encoded CA cert file to use to verify
  the Nomad server SSL certificate.

- `ca_path` `(string: "")` - Path to a directory of PEM encoded CA cert files to
  verify the Nomad server SSL certificate.

- `client_cert` `(string: "")` - Path to a PEM encoded client certificate for TLS
  authentication to the Nomad server.

- `client_key` `(string: "")` - Path to an unencrypted PEM encoded private key
  matching the client certificate.

- `tls_server_name` `(string: "")` - The server name to use as the SNI host when
  connecting via TLS.

- `skip_verify` `(bool: false)` - Do not verify TLS certificates. This is strongly
  discouraged.

## `policy` Block

The `policy` block configures the Nomad Autoscaler's policy handling.

```hcl
policy {
  dir              = "/opt/nomad-autoscaler/plugins"
  default_cooldown = "2m"
}
```

### `policy` Parameters

- `dir` `(string: "./plugins")` - The path to a directory used to load scaling
  policies.

- `default_cooldown` `(string: "5m")` - The default cooldown that will be applied
  to all scaling policies which do not specify a cooldown period.

- `default_evaluation_interval` `(string: "10s")` - The default evaluation interval
  that will be applied to all scaling policies which do not specify an evaluation
  interval.

## `apm` Block

The `apm` block is used to configure application performance metric (APM) plugins.

```hcl
apm "example-apm-plugin" {
  driver = "example-apm-plugin"
  args   = ["-my-flag"]

  config = {
    address = "http://127.0.0.1:9090"
  }
}
```

### `apm` Parameters

- `args` `(array<string>: [])` - Specifies a set of arguments to pass to the
  plugin binary when it is executed.

- `driver` `(string: "")` - The plugin's executable name relative to to the
  plugin_dir. If the plugin has a suffix, such as .exe, this should be omitted.

- `config` `(map<string><string>: nil)` - Specifies configuration values for
  the plugin either as HCL or JSON. The accepted values are plugin specific.
  Please refer to the individual plugin's documentation.

## `target` Block

The `target` block is used to configure scaling target plugins.

```hcl
target "example-target-plugin" {
  driver = "example-target-plugin"
  args   = ["-my-flag"]

  config = {
    region = "esp-vlc-1"
  }
}
```

### `target` Parameters

- `args` `(array<string>: [])` - Specifies a set of arguments to pass to the
  plugin binary when it is executed.

- `driver` `(string: "")` - The plugin's executable name relative to to the
  plugin_dir. If the plugin has a suffix, such as .exe, this should be omitted.

- `config` `(map<string><string>: nil)` - Specifies configuration values for
  the plugin either as HCL or JSON. The accepted values are plugin specific.
  Please refer to the individual plugin's documentation.

## `strategy` Block

The `strategy` block is used to configure scaling strategy plugins.

```hcl
strategy "example-strategy-plugin" {
  driver = "example-strategy-plugin"
  args   = ["-my-flag"]

  config = {
    algorithm = "complex"
  }
}
```

### `strategy` Parameters

- `args` `(array<string>: [])` - Specifies a set of arguments to pass to the
  plugin binary when it is executed.

- `driver` `(string: "")` - The plugin's executable name relative to to the
  plugin_dir. If the plugin has a suffix, such as .exe, this should be omitted.

- `config` `(map<string><string>: nil)` - Specifies configuration values for
  the plugin either as HCL or JSON. The accepted values are plugin specific.
  Please refer to the individual plugin's documentation.

[hcl_v2]: https://github.com/hashicorp/hcl/tree/hcl2
[nomad_namespaces]: https://learn.hashicorp.com/nomad/governance-and-policy/namespaces
[nomad_acls]: https://learn.hashicorp.com/nomad?track=acls#acls
[autoscaler_cli_config]: /docs/autoscaling/cli#config
[autoscaler_cli_policy_dir]: /docs/autoscaling/cli#policy-dir