How to make RUST run gracefully in the background and daemonize？ - service

Question

This is what i want to achieve
root> ./webserver start // Does not block the terminal after startup, runs in the background and the process is guarded
root>
My current implementation logic：
Logic running in the background
use std::process::Command;
use std::thread;
use std::env;
use std::time::Duration;
fn main() {
let args: Vec<String> = env::args().collect();
if args.len() == 2 {
if &args[1] == "start" {
// Main process start child process
let child = Command::new(&args[0])
.spawn().expect("Child process failed to start.");
println!("child pid: {}", child.id());
// Main process exit
}
} else {Is there any more elegant approach? Looking forward to your reply
// Main business logic
run webserver
}
}
In this way, rust will run in the background without blocking the terminal, but the information printed by rust in the background will still be displayed on the terminal, and the current rust program will exit when exiting the terminal
Process daemon logic
My idea is to monitor the exit signal of the system and not process the exit request
SIGHUP 1 /* Hangup (POSIX). */
SIGINT 2 /* Interrupt (ANSI). */
SIGQUIT 3 /* Quit (POSIX). */
SIGTERM 15 /* Termination (ANSI). */
code:
use signal_hook::{iterator::Signals, SIGHUP,SIGINT,SIGQUIT,SIGTERM};
use std::{thread, time::Duration};
pub fn process_daemon() {
let signals = match Signals::new(&[SIGHUP,SIGINT,SIGQUIT,SIGTERM]) {
Ok(t) => t,
Err(e) => panic!(e),
};Is there any more elegant approach? Looking forward to your reply
thread::spawn(move || {
for sig in signals.forever() {
println!("Received signal {:?}", sig);
}
});
thread::sleep(Duration::from_secs(2));
}
Is there any more elegant approach? Looking forward to your reply.

Answer 1

TLDR: if you really want your process to act like a service (and never quit), probably do the work to set up a service manager. Otherwise, just let it be a normal process.
Daemonizing a Process
One thing to notice right off the bat is that most of the considerations about daemonizing have nothing to do with Rust as a language and are more about:
The underlying system your processes are targeted for
The exact behavior of your daemon processes once spawned
By looking at your question, it seems you have realized most of this. Unfortunately to properly answer your question we have to delve a bit into the intricacies of processes and how they are managed. It should be noted that existing 'service' managers are a great solution if you are OK with significant platform dependence in your launching infrastructure.
Linux: systemd
FreeBSD: rc
MacOS: launchd
Windows: sc
As you can see, no simple feat if you want to have a simple deployment that just works (provided that it is compiled for the relevant system). These are just the bare metal service managers. If you want to support virtual environments you will have to think about Kubernetes services, dockerizing, etc.
These tools exist because there are many considerations to managing a long-running process on a system:
Should my daemon behave like a service and respawn if killed (or if the system is rebooted)? The tools above will allow for this.
If a service, should my daemon have status states associated with it to help with maintenance? This can help with managing outages and building tooling to scale horizontally.
If the daemon shouldn't be a service (unlikely in your case given your binary's name) there are even more questions: should it be attached to the parent process? Should it be attached to the login process group?
My guess for your process given how complex this can become, simply run the process directly. Don't daemonize at all.
For testing, (if you are in a unix-like environment) you can run your process in the background:
./webserver start &
This will spawn the new process in the background, but attach it to your shell's process list. This can be nice for testing, because if that shell goes away the system will clean up these attached processes along with it.
The above will direct stderr and stdout file descriptors back to your terminal and print them. If you wish to avoid that, you can always redirect the output somewhere else.
Disabling signals to a process like this doesn't seem like the right approach to me. Save these signals to gracefully exit your process once you need to save state or send a termination message to a client. If you do the above, your daemon will only be killable by a kill -9 <pid> or rebooting, or finding some non-standard signal you haven't overridden whose default behavior is to terminate.