Snap Plugin Library for Go

This is a library for writing plugins in Go for the Snap telemetry framework.

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1. Writing a Plugin
   • Before Writing a Snap Plugin
2. Brief Overview of Snap Architecture
3. Example Plugins
4. Plugin Flags
   • Custom Config
   • Plugin Diagnostics
   • Custom Flags

Writing a Plugin

Snap has three different plugin types and for instructions on how to write a plugin check out the collector, processor, and publisher plugin docs.

Before writing a Snap plugin:

• See if one already exists in the Plugin Catalog
• See if someone mentioned it in the plugin wishlist

If you do decide to write a plugin check out the plugin authoring docs and let us know you are working on one!

Brief Overview of Snap Architecture:

Snap is an open and modular telemetry framework designed to simplify the collection, processing and publishing of data through a single HTTP based API. Plugins provide the functionality of collection, processing and publishing and can be loaded/unloaded, upgraded and swapped without requiring a restart of the Snap daemon.

A Snap plugin is a program that responds to a set of well defined gRPC services with parameters and return types specified as protocol buffer messages (see plugin.proto). The Snap daemon handshakes with the plugin over stdout and then communicates over gRPC.

Snap Plugin Go Library Examples:

You will find example plugins that cover the basics for writing collector, processor, and publisher plugins in the examples folder.

Plugin Flags:

For specific details and to see all the options when running, run the plugin with the -help flag. The flag options are:

GLOBAL OPTIONS:
   --config value            config to use in JSON format
   --port value              port GRPC will listen on
   --pprof                   enable pprof
   --tls                     enable TLS
   --cert-path value         necessary to provide when TLS enabled
   --key-path value          necessary to provide when TLS enabled
   --root-cert-paths value   root paths separated by ':'
   --stand-alone             enable stand alone plugin
   --stand-alone-port value  specify http port when stand-alone is set (default: 8181)
   --log-level value         log level - 0:panic 1:fatal 2:error 3:warn 4:info 5:debug (default: 2)
   --required-config         Plugin requires config passed in
   --help, -h                show help
   --version, -v             print the version

Additionally, plugin authors can add custom flags as described here

Custom Config:

Users can provide their own config with the -config flag. If a config is required for the plugin to load, diagnostics will show a warning describing which keys are required and not provided.

When using the -config flag, it expects a parameter in the form of a JSON. This is of the form '{}'. An example config is: -config '{\"key\":\"kelly\", \"spirit-animal\":\"coatimundi\"}'.

Plugin Diagnostics:

Snap plugins using plugin-lib-go can be run independent of Snap to show their current running diagnostics.

Running plugin diagnostics is easy! Simply build the plugin, then run the executable $./build/${GOOS}/${GOARCH}/<plugin binary>.

Diagnostic information includes:

• Runtime details
  • Plugin version
  • RPC type and version
  • OS, architecture
  • Golang version
• Warning if dependencies not met
• Config policy (for collector plugins only)
  • Warning if config items required and not provided
• Collectable metrics (for collector plugins only)
• How long it took to run each of these diagnostics

Currently Snap Plugin Diagnostics is only available for collector plugins.

Custom Flags

Plugins authors using snap-plugin-lib-go have the ability to create customized runtime flags. These flags are written using urfave/cli. An example of a custom flag in a plugin can be found in the snap-plugin-collector-rand example.

Flags can be added with the following syntax:

plugin.AddFlag(
		cli.BoolFlag{
			Name:        "required-config",
			Hidden:      false,
			Usage:       "Plugin requires config passed in",
			Destination: &req,
		},
	)

More information about types of cli flags and options for each flag can be found in the documentation for urfave/cli

As always, if you have any questions, please reach out to the Snap team via Slack or by opening an issue in github.