open-nomad/website/source/docs/internals/plugins/base.html.md

layout	page_title	sidebar_current	description
docs	Base Plugin	docs-internals-plugins-base	Learn about how to author a Nomad plugin.

Base Plugin

The base plugin is a special plugin type implemented by all plugins. It allows for common plugin operations such as defining a configuration schema and version information.

Plugin API

PluginInfo() (*PluginInfoResponse, error)

A PluginInfoResponse contains meta data about the plugin.

PluginInfoResponse{
    // Type is the plugin type which is implemented
    Type: PluginTypeDriver,
    // Plugin API versions supported by the plugin
    PluginApiVersions: []string{drivers.ApiVersion010},
    // Version of the plugin
    PluginVersion: "0.1.0",
    // Name of the plugin
    Name: "foodriver",
}

ConfigSchema() (*hclspec.Spec, error)

The ConfigSchema function allows a plugin to tell Nomad the schema for it's configuration. This configuration is given in a plugin block of the client configuration. The schema is defined with the hclspec package.

SetConfig(config *Config) error

The SetConfig function is called when starting the plugin for the first time. The Config given has two different configuration fields. The first PluginConfig, is an encoded configuration from the plugin block of the client config. The second, AgentConfig, is the Nomad agent's configuration which is given to all plugins.

HCL Specifications

*hclspec.Spec is a struct that defines the schema to validate an HCL entity against. The full documentation of the different hcl attribute types can be found on the hclspec godoc.

For a basic example, lets look at the driver configuration for the raw_exec driver:

job "example" {
...
      driver = "raw_exec"
      config {
        command = "/bin/sleep"
        args = ["100"] 
      }
}

The config block is what is validated against the hclspec.Spec. It has two keys, command which takes a string attribute and args which takes an array attribute. The corresponding *hclspec.Spec would be:

    spec :=  hclspec.NewObject(map[string]*hclspec.Spec{
		"command": hclspec.NewAttr("command", "string", true),
		"args":    hclspec.NewAttr("args", "list(string)", false),
	})