Golang: How to auto-restart process when binary updated? - go

Question

I built the golang app in local, then scp to server. I need to stop the process and restart manually. Is there any way to auto-restart the process when binary updated?

Answer 1

While this is generally better to be implemented off-process using something like daemontools or similar, there are some cases when you want/need it to be done inside your program.
Doing it inside your program can be tricky depending on the program characteristics such as connections or files it may have open, etc.
Having said that, here you have an implementation which would work in most cases:
package main
import (
"log"
"os"
"syscall"
"time"
"github.com/fsnotify/fsnotify"
"github.com/kardianos/osext"
)
func setupWatcher() (chan struct{}, error) {
file, err := osext.Executable()
if err != nil {
return nil, err
}
log.Printf("watching %q\n", file)
w, err := fsnotify.NewWatcher()
if err != nil {
return nil, err
}
done := make(chan struct{})
go func() {
for {
select {
case e := <-w.Events:
log.Printf("watcher received: %+v", e)
err := syscall.Exec(file, os.Args, os.Environ())
if err != nil {
log.Fatal(err)
}
case err := <-w.Errors:
log.Printf("watcher error: %+v", err)
case <-done:
log.Print("watcher shutting down")
return
}
}
}()
err = w.Add(file)
if err != nil {
return nil, err
}
return done, nil
}
func main() {
log.Print("program starting")
watcher, err := setupWatcher()
if err != nil {
// do something sensible
log.Fatal(err)
}
// continue with app startup
time.Sleep(100 * time.Minute) // just for testing
// eventually you may need to end the watcher
close(watcher) // this way you can
}
Then you do
% go build main.go
% ./main
2016/12/29 14:15:06 program starting
2016/12/29 14:15:06 watching "/home/plalloni/tmp/v/main"
And here the output it produced after you run (in other terminal) some successive "go build main.go" (which "updates" the running binary).
2016/12/29 14:15:32 watcher received: "/home/plalloni/tmp/v/main": CHMOD
2016/12/29 14:15:32 program starting
2016/12/29 14:15:32 watching "/home/plalloni/tmp/v/main"
2016/12/29 14:15:38 watcher received: "/home/plalloni/tmp/v/main": CHMOD
2016/12/29 14:15:38 program starting
2016/12/29 14:15:38 watching "/home/plalloni/tmp/v/main"
Hope it helps.

Answer 2

You can use https://github.com/slayer/autorestart
package main
import "github.com/slayer/autorestart"
func main() {
autorestart.StartWatcher()
http.ListenAndServe(":8080", nil) // for example
}

Answer 3

Does it need to be sophisticated? You could have entr running and trigger an updater script when the binary changes.
http://entrproject.org/
e.g.
echo 'binary_path' | entr script.sh &

Answer 4

I have a resolution about this case.
See also.
https://github.com/narita-takeru/cmdrevive
example
cmdrevive ./htmls/ ".html$" (application) (arguments)
So, this case applicable.
cmdrevive "/(app path)" "(app filename)" (app full path) (arguments)
If (app filename) changed on (app path) directory, then restart (app full path) with (arguments).
How about this one?