Telegraf Execd Go Shim

The goal of this shim is to make it trivial to extract an internal input, processor, or output plugin from the main Telegraf repo out to a stand-alone repo. This allows anyone to build and run it as a separate app using one of the execd plugins:

• inputs.execd
• processors.execd
• outputs.execd

Steps to externalize a plugin

1. Move the project to an external repo, it's recommended to preserve the path structure, (but not strictly necessary). eg if your plugin was at plugins/inputs/cpu, it's recommended that it also be under plugins/inputs/cpu in the new repo. For a further example of what this might look like, take a look at ssoroka/rand or danielnelson/telegraf-plugins
2. Copy main.go into your project under the cmd folder. This will be the entrypoint to the plugin when run as a stand-alone program, and it will call the shim code for you to make that happen. It's recommended to have only one plugin per repo, as the shim is not designed to run multiple plugins at the same time (it would vastly complicate things).
3. Edit the main.go file to import your plugin. Within Telegraf this would have been done in an all.go file, but here we don't split the two apart, and the change just goes in the top of main.go. If you skip this step, your plugin will do nothing. eg: _ "github.com/me/my-plugin-telegraf/plugins/inputs/cpu"
4. Optionally add a plugin.conf for configuration specific to your plugin. Note that this config file must be separate from the rest of the config for Telegraf, and must not be in a shared directory where Telegraf is expecting to load all configs. If Telegraf reads this config file it will not know which plugin it relates to. Telegraf instead uses an execd config block to look for this plugin.

Steps to build and run your plugin

1. Build the cmd/main.go. For my rand project this looks like go build -o rand cmd/main.go
2. If you're building an input, you can test out the binary just by running it. eg ./rand -config plugin.confDepending on your polling settings and whether you implemented a service plugin or an input gathering plugin, you may see data right away, or you may have to hit enter first, or wait for your poll duration to elapse, but the metrics will be written to STDOUT. Ctrl-C to end your test. If you're testing a processor or output manually, you can still do this but you will need to feed valid metrics in on STDIN to verify that it is doing what you want. This can be a very valuable debugging technique before hooking it up to Telegraf.
3. Configure Telegraf to call your new plugin binary. For an input, this would look something like:

[[inputs.execd]]
  command = ["/path/to/rand", "-config", "/path/to/plugin.conf"]
  signal = "none"

Refer to the execd plugin readmes for more information.

Congratulations

You've done it! Consider publishing your plugin to github and open a Pull Request back to the Telegraf repo letting us know about the availability of your external plugin.