watchGoD v0.1

A process manager in golang with some novel ideas.

• Complex blocks in your stack (such as a 100kloc backend binary) should be checked and controlled by simpler blocks (for example a 50loc program that checks if website is still up). In watchgod, these simpler blocks are called loaders.

• The loader of your binary can be included in binary itself. This keeps your loader close to the more complex logic it manages.

• Loaders should not have too much state: should be safe to reload them at any time.

• Loaders could be used to pass over a server's accept()-fd when it eventually needs to reload for hot code reloading. (not implemented yet)

For golang programs, you can use the watchgod library to create definitions in your binary's init() function. Example:

package main

import (
	"net/http"
	"github.com/emielm/watchgod"
)

func main() {
	http.ListenAndServe(":80", myBackend)
}

func init() {
	job := watchgod.Job("backend")
	job.Auto = true
	job.Exec = []string{os.Args[0]}
	job.Check = func() string {
		return "ok"
	}

	job = watchgod.Job("postgres")
	job.Auto = true
	job.Exec = []string{"/usr/lib/postgresql/9.5/bin/postgres", "-D", "data/db"}

	watchgod.Init()
}

This is an early, experimental release. Do not use in production just yet.

Installation and usage

go get -u github.com/emielm/watchgod/...

This repository contains both the golang library (watchgod.go) and the god command (cmd/god/main.go).

Compile/symlink your watchgod-compatible binaries to build/god and start with god --dir build/god.

Loader protocol

All executable binaries in the god/ directory should support the special invocation with godv1 as argv[1]. In that case, they should speak the line-based json loader protocol over stdin/stdout.

TODO

• Job states in transition diagram
• Think about auto-start implementation and how to improve
• More consistent signal handling
• Rethink the request/response json wire protocol to allow async checks that take longer
• Implement stdout/stderr transformations
• Get a server's accept-FD handover to work through loader
• Test more in production envs