Horust is a supervisor / init system written in rust and designed to be run inside containers.

Table of contents

• Goals
• Status
• Usage
• Contributing
• License

Goals

• Supervision: A fully-featured supervision system, designed to be run in containers (but not exclusively).
• Simplicity: Clear, modifiable, and removable code as needed.
• Completeness: A seamless drop-in for any init system.
• Reliability: Stability and trustworthiness across all use cases.

Status

This should be considered Beta software. You can (and should) use it, but under your own discretion. Please report any issue you encounter, or also sharing your use cases would be very helpful. Horust can be used on macOS in development situations. Due to limitations in the macOS API, subprocesses of supervised processes may not correctly be reaped when their parent process exits.

Usage

Being a supervision and init system, it can be used to start and manage a bunch of processes. You can use it to supervise a program and, for example, restart it in case it exists with an error. Or startup dependencies like start a webserver after starting a database.

Quick tutorial

As a simple example, assume you'd like to host your rest api. This is the code:

from http.server import BaseHTTPRequestHandler, HTTPServer

class Handler(BaseHTTPRequestHandler):
    def do_GET(self):
         if self.path == "/user":
            raise Exception("Unsupported path: /user")  # Exception will kill the server
        self.send_response(200)
        self.send_header("Content-type", "text/plain")
        self.end_headers()
        self.wfile.write(b"Hello, World!")

HTTPServer(('', 8000), Handler).serve_forever()

you can run it using python3 myapp.py. If you go to localhost:8000/user, unfortunately, the server will fail. Now you need to manually restart it!

Let's see how we can use horust to supervise it and restart it in case of failure.

1. Create your first Horust service:

Tip

You can also bootstrap the creation of a new service, by using horust --sample-service > new_service.toml.

We are now going to create a new config file for our service. They are defined in TOML and the default path where horust will look for service is in /etc/horust/services/.

Note

It's possible to run a one-shot instance just by doing horust myprogram without defining a service config file.

Let's create a new service under /etc/horust/services/healthchecker.toml:

command = "/tmp/myapp.py"
[restart]
strategy = "always"

There are many supported properties for your service file, but only command is required.

On startup, Horust will read this service file, and run the command after waiting for 10 seconds. According to the restart strategy "never", as soon as the service has carried out its task it will restart.

As you can see, it will run the /tmp/myapp.py Python script, which doesn't exist yet. Let's create it!

2. Create your app:

Create a new file script under /tmp/myapp.py:

#!/usr/bin/env python3
from http.server import BaseHTTPRequestHandler, HTTPServer

class Handler(BaseHTTPRequestHandler):
    def do_GET(self):
        if self.path == "/user":
            raise Exception("Unsupported path: /user")  # Exception will kill the server
        self.send_response(200)
        self.send_header("Content-type", "text/plain")
        self.end_headers()
        self.wfile.write(b"Hello, World!")

HTTPServer(('', 8000), Handler).serve_forever()

And remember to make it executable:

chmod +x /tmp/api.py

3. Get the latest release or build from source:

You can grab the latest release from the releases page. Or if you like to live on the edge, scroll down to the building section.

4. Run Horust:

Now you can just:

./horust --uds-folder-path /tmp

Tip

Horustctl is a program that allows you to interact with horust. They communicate using Unix Domain Socket (UDS), and by default horust stores the sockets in /var/run/horust. In this example, we have overridden the path by using the argument --uds-folder-path.

Try navigating to http://localhost:8000/. A page with Hello world should be greeting you.

Now try navigating to http://localhost:8000/user - you should get a "the connection was reset" error page. Checking on your terminal, you will see that the program has raised the exception, as we expected. Now, try navigating again to http://localhost:8000/ and the website is still up and running.

Pretty nice uh? One last thing!

If you downloaded a copy of horustctl, you can also do:

horustctl --uds-folder-path /tmp status myapp.toml

To check the status of your service. Currently, horustctl only support querying for the service status.

5. Wrapping up

Use Ctrl+C to stop Horust. Horust will send a SIGTERM signal to all the running services, and if it doesn't hear back for a while - it will terminate them by sending an additional SIGKILL signal. Wait time and signals are configurable.

---

Check out the documentation for a complete reference of the options available on the service config file. A general overview is available below as well:

command = "/bin/bash -c 'echo hello world'"
start-delay = "2s"
start-after = ["database", "backend.toml"]
stdout = "STDOUT"
stdout-rotate-size = "100MB"
stdout-should-append-timestamp-to-filename = false
stderr = "/var/logs/hello_world_svc/stderr.log"
user = "root"
working-directory = "/tmp/"

[restart]
strategy = "never"
backoff = "0s"
attempts = 0

[healthiness]
http-endpoint = "http://localhost:8080/healthcheck"
file-path = "/var/myservice/up"

[failure]
successful-exit-code = [0, 1, 255]
strategy = "ignore"

[termination]
signal = "TERM"
wait = "10s"
die-if-failed = ["db.toml"]

[environment]
keep-env = false
re-export = ["PATH", "DB_PASS"]
additional = { key = "value" } 

Building

For building Horust, you will need Rust and protoc compiler. Protoc is used for interacting with horust through horustctl. As soon as both are installed, you can build Horust with:

cargo build --release

Contributing

Thanks for considering contributing to horust! To get started, have a look at CONTRIBUTING.md.

License

Horust is provided under the MIT license. Please read the attached license file.