jeremyben · February 20, 2024 06:07
diff --git a/myapp.service b/myapp.service
 # https://www.freedesktop.org/software/systemd/man/systemd.unit.html
 [Unit]
 Description=My App
 After=network.target

 # https://www.freedesktop.org/software/systemd/man/systemd.exec.html
 [Service]
 Type=simple
 # https://www.freedesktop.org/software/systemd/man/systemd.exec.html#WorkingDirectory=
 WorkingDirectory=-/srv/app/
 ExecStart=/usr/bin/node server.js
 DynamicUser=yes
 ProtectHome=yes
 Restart=always
 StandardOutput=syslog
 StandardError=syslog
 SyslogIdentifier=myapp

 [Install]
 WantedBy=multi-user.target
diff --git a/myapp.socket b/myapp.socket
 # https://www.freedesktop.org/software/systemd/man/systemd.socket.html

 [Socket]
 # https://www.freedesktop.org/software/systemd/man/systemd.socket.html#ListenStream=
 ListenStream=3000
 BindIPv6Only = both

 # SO_REUSEPORT not supported by node: https://github.com/nodejs/node/issues/12228
 # ReusePort=true

 [Install]
 WantedBy=sockets.target
diff --git a/server.ts b/server.ts
 import http from 'http'
 import { getSystemdSocketHandle } from './socket-handle'

 const server = http.createServer(async (req, res) => {
 	console.log(req.url, req.headers)

 	res.statusCode = 200
 	res.setHeader('Content-Type', 'application/json')
 	res.end(JSON.stringify({ data: true }))
 })

 // Still compatible if not socket activated.
 const handle = getSystemdSocketHandle() || process.env.PORT || 3000

 server.listen(handle, () => {
 	console.log('Server started', server.address())
 })
diff --git a/socket-handle.ts b/socket-handle.ts
 /**
 * Returns file descriptor of systemd socket.
 * Returns `undefined` if the process has not been activated by systemd socket.
 */
 export function getSystemdSocketHandle() {
 	// https://www.freedesktop.org/software/systemd/man/sd_listen_fds.html
 	const SD_LISTEN_FDS_START = 3

 	const LISTEN_PID = !!process.env.LISTEN_PID && Number.parseInt(process.env.LISTEN_PID)
 	const LISTEN_FDS = !!process.env.LISTEN_FDS && Number.parseInt(process.env.LISTEN_FDS)
 	const LISTEN_FDNAMES = !!process.env.LISTEN_FDNAMES && process.env.LISTEN_FDNAMES.split(':')

 	// console.log('PID:', process.pid, 'PPID:', process.ppid)
 	// console.log('LISTEN_PID:', LISTEN_PID, 'LISTEN_FDS:', LISTEN_FDS, 'LISTEN_FDNAMES:', LISTEN_FDNAMES)

 	const isSocketActivated = !!LISTEN_PID && !!LISTEN_FDS

 	if (!isSocketActivated) {
 		return undefined
 	}

 	if (LISTEN_PID !== process.pid) {
 		throw Error(`Cannot use file descriptors meant for pid ${LISTEN_PID} in pid ${process.pid}`)
 	}

 	if (LISTEN_FDS > 1) {
 		throw Error(`One file descriptor expected. ${LISTEN_FDS} received (${LISTEN_FDNAMES})`)
 	}

 	return { fd: SD_LISTEN_FDS_START }
 }
diff --git a/§links.md b/§links.md
	# https://www.freedesktop.org/software/systemd/man/systemd.unit.html
	[Unit]
	Description=My App
	After=network.target

	# https://www.freedesktop.org/software/systemd/man/systemd.exec.html
	[Service]
	Type=simple
	# https://www.freedesktop.org/software/systemd/man/systemd.exec.html#WorkingDirectory=
	WorkingDirectory=-/srv/app/
	ExecStart=/usr/bin/node server.js
	DynamicUser=yes
	ProtectHome=yes
	Restart=always
	StandardOutput=syslog
	StandardError=syslog
	SyslogIdentifier=myapp

	[Install]
	WantedBy=multi-user.target
	# https://www.freedesktop.org/software/systemd/man/systemd.socket.html

	[Socket]
	# https://www.freedesktop.org/software/systemd/man/systemd.socket.html#ListenStream=
	ListenStream=3000
	BindIPv6Only = both

	# SO_REUSEPORT not supported by node: https://github.com/nodejs/node/issues/12228
	# ReusePort=true

	[Install]
	WantedBy=sockets.target
	import http from 'http'
	import { getSystemdSocketHandle } from './socket-handle'

	const server = http.createServer(async (req, res) => {
	console.log(req.url, req.headers)

	res.statusCode = 200
	res.setHeader('Content-Type', 'application/json')
	res.end(JSON.stringify({ data: true }))
	})

	// Still compatible if not socket activated.
	const handle = getSystemdSocketHandle() \|\| process.env.PORT \|\| 3000

	server.listen(handle, () => {
	console.log('Server started', server.address())
	})
	/**
	* Returns file descriptor of systemd socket.
	* Returns `undefined` if the process has not been activated by systemd socket.
	*/
	export function getSystemdSocketHandle() {
	// https://www.freedesktop.org/software/systemd/man/sd_listen_fds.html
	const SD_LISTEN_FDS_START = 3

	const LISTEN_PID = !!process.env.LISTEN_PID && Number.parseInt(process.env.LISTEN_PID)
	const LISTEN_FDS = !!process.env.LISTEN_FDS && Number.parseInt(process.env.LISTEN_FDS)
	const LISTEN_FDNAMES = !!process.env.LISTEN_FDNAMES && process.env.LISTEN_FDNAMES.split(':')

	// console.log('PID:', process.pid, 'PPID:', process.ppid)
	// console.log('LISTEN_PID:', LISTEN_PID, 'LISTEN_FDS:', LISTEN_FDS, 'LISTEN_FDNAMES:', LISTEN_FDNAMES)

	const isSocketActivated = !!LISTEN_PID && !!LISTEN_FDS

	if (!isSocketActivated) {
	return undefined
	}

	if (LISTEN_PID !== process.pid) {
	throw Error(`Cannot use file descriptors meant for pid ${LISTEN_PID} in pid ${process.pid}`)
	}

	if (LISTEN_FDS > 1) {
	throw Error(`One file descriptor expected. ${LISTEN_FDS} received (${LISTEN_FDNAMES})`)
	}

	return { fd: SD_LISTEN_FDS_START }
	}