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Creating a Go based plugin for snap through a stripped down example

  1. Choose a repository and plugin name
  • It is suggested that your name include the following convention snap-plugin-[plugin-type]-[plugin-name]
  • For example: snap-plugin-collector-foo
  • Plugin types: collector, processor, publisher
  1. Implement the CollectorPlugin interface (cpuid.go)
// Collector plugin
type CollectorPlugin interface {
   Plugin
   CollectMetrics([]PluginMetricType) ([]PluginMetricType, error)
   GetMetricTypes(PluginConfigType) ([]PluginMetricType, error)
}```
```go
type Plugin interface {
   GetConfigPolicy() (*cpolicy.ConfigPolicy, error)
}
  • GetMetricTypes([]PluginMetricType) ([]PluginMetricType, error) communicates what metrics the plugin collects through returning an array of plugin.PluginMetricType
    • Through the plugin.PluginMetricType we are providing the namespace and version of the metric(s) our plugin will provide
// GetMetricTypes returns the metrics this plugin provides through an array of plugin.PluginMetricType
func (c *CPUID) GetMetricTypes(_ plugin.PluginConfigType) ([]plugin.PluginMetricType, error) {
   return []plugin.PluginMetricType{
   	plugin.PluginMetricType{
   		Namespace_: []string{"jcooklin", "cpuid", "VendorIdentificationString"},
   		Version_: 1,
   	},
   }, nil
}

  • CollectMetrics(mts []plugin.PluginMetricType) ([]plugin.PluginMetricType, error) returns the requested metrics

    • The argument to CollectMetrics is an array of plugin.PluginMetricType where the Namespace field communicates what metric is being requested
    • The result of CollectMetrics is also an array of plugin.PluginMetricType where the fields Data, TimeStamp and Source communicate the value, time of collection and source of the metric
    // CollectMetrics returns []plugin.PluginMetrictType

func (c *CPUID) CollectMetrics(mts []plugin.PluginMetricType) ([]plugin.PluginMetricType, error) { hostname, _ := os.Hostname() for idx, m := range mts { switch m.Namespace_[len(m.Namespace_)-1] { case "VendorIdentificatorString": mts[idx].Data_ = cpuid.VendorIdentificatorString mts[idx].Timestamp_ = time.Now() mts[idx].Source_ = hostname } } return mts, nil } ```

  • GetConfigPolicy() (*cpolicy.ConfigPolicy, error) returns the required config policy, if any, for the metrics provided by the plugin
    • This plugin does not require a config policy so an empty cpolicy is returned
    // GetConfigPolicy returns the policy for this plugin

func (c *CPUID) GetConfigPolicy() (*cpolicy.ConfigPolicy, error) { return cpolicy.New(), nil } ``` * Note: a config policy provides the plugin author a mechanism which forces the users of the plugin to provide configuration detail such as username, password, address, port, etc when their plugin is used

  • Start the plugin (main.go)
    • plugin.Start(m *PluginMeta, c Plugin, requestString string) starts the plugin
      func main() {
  c := &cpuid.CPUID{}
  plugin.Start(
  	cpuid.Meta(),
  	c,
  	os.Args[1],
  )

}

    * `cpuid.Meta()` returns `*PluginMeta`    	   
  	```go
	func Meta() *plugin.PluginMeta {
		return plugin.NewPluginMeta(
			name,
			version,
			pluginType,
			[]string{plugin.SnapGOBContentType},
			[]string{plugin.SnapGOBContentType})
	}

Download, build and use the plugin

  1. Use 'go get' to get the plugin
go get github.com/jcooklin/snap-plugin-collector-cpuid

Note The rest of the commands below are run from the root of the snap-plugin-collector-cpuid which should now be located at $GOPATH/src/github.com/jcooklin/

  • Build the plugin
make
  • Start snapd
snapd -t 0 -l 1

  • -t 0 disables plugin trust

  • -l 1 starts snapd with debug logging

  • Load plugins

snapctl plugin load build/rootfs/snap-plugin-collector-cpuid
snapctl plugin load ../../intelsdi-x/snap/build/plugin/snap-publisher-file

Note: You may need to reference a different path for the snap-publisher-file. For instance, if you downloaded a release.

  • Start task
snapctl task create -t example/task.json
  • Watch task
snapctl task watch <TASK_ID>

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