ProcFusion

Very simple process manager for your Docker images.

Introduction

One container, one application. That is the mantra we should follow when designing a container based application.

However, one application can sometimes be split into multiple processes. When that is the case, it can become challenging to manage those processes within a Docker image.

Solutions like supervisord can help, but they come with their own quirks, for example:

• supervisord restart the child processes by default
• supervisord logs the child process's stdout/stderr to a file by default
• when redirected to stdout/stderr instead, the logs are mixed and not easily filterable

Also, requiring Python in your Docker container can be a huge overhead, especially if your application is not written in Python.

ProcFusion aims to solve this.

Features

• start each child process in a process group
• if SIGINT/SIGTERM/SIGHUP is sent to ProcFusion, it forwards it to each child process
• if a process exits (normally or not), ProcFusion sends SIGTERM to every other child process, and exits with the exited process's exit code
• prefix stdout/stderr of each process with a deterministic label

Comparison

Feature	ProcFusion	Supervisord	s6-overlay	dumb-init
Process Groups	✅	✅	✅	✅
Forward signals	✅	✅	✅	✅
Multiple children	✅	✅	✅	❌
Dependency management	❌	❌	✅	❌
Logs prefixing	✅	❌	❌	❌
Configuration	TOML	INI-like	Service files	Command-line or as shebang
Language (not that it matters)	Rust	Python	Shell	C

Installation

$ cargo install --git https://github.com/linkdd/procfusion

Or download the archive from the latest release.

Usage

ProcFusion expects its configuration as a TOML file:

[processes.foo]
command = "while true; do echo foo; sleep 1; done"
shell = "/bin/sh"   # Wraps command in '/bin/sh -c'
directory = "/tmp"  # Optional, defaults to $PWD

[processes.bar]
command = "while true; do echo bar; sleep 2; done"
shell = "/bin/sh"

[processes.baz]
command = "for i in 1 2; do echo baz; sleep 3; done; exit 1"
shell = "/bin/sh"

Then run:

$ procfusion path/to/config.toml

The example above will have the following output:

proc.foo[stdout]   | foo: hello
proc.bar[stdout]   | bar
proc.baz[stdout]   | baz
proc.foo[stdout]   | foo: hello
proc.bar[stdout]   | bar
proc.foo[stdout]   | foo: hello
proc.baz[stdout]   | baz
proc.foo[stdout]   | foo: hello
proc.bar[stdout]   | bar
proc.foo[stdout]   | foo: hello
proc.foo[stdout]   | foo: hello
controller[stdout] | time=2024-05-15T12:18:50.247868783Z message="baz exited with exit status: 1"
controller[stdout] | time=2024-05-15T12:18:50.248983822Z message="bar exited with signal: 15 (SIGTERM)"
controller[stdout] | time=2024-05-15T12:18:50.249275312Z message="foo exited with signal: 15 (SIGTERM)"

NB: Environment variables are inherited from the ProcFusion process.

License

This software is distributed under the terms of the MIT License.