A Docker entry point script that manages multiple daemons/services

entrypoint.sh

#!/bin/bash
# Bash 4+ requred

# Copyright 2025 Guiorgy
# 
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
# 
# - The above copyright notice and this permission notice shall be included in
#   all copies or substantial portions of the Software.
# 
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.

# Make sure we are running as root
if [[ "$(id -u)" -ne 0 ]]; then
	echo 1>&2 'This script must be run as root'
	exit 1
fi

# The daemons to manage
declare -A daemons
# Key: Process name
# Value: Executable
daemons['service1']='/usr/bin/service1'
daemons['service2']='/usr/bin/service2'

# CLI arguments for the daemon executables
declare -A arguments
# Key: Process name
# Value: Arguments
# Services with no args can be skipped
arguments['service1']='-c /config.json'

# Whether the daemon executables fork internally and exit
declare -A forking
# Key: Process name
# Value: 0 for normal; 1 for forking
# Skipped entries will be set to 0 by default
arguments['service1']=1

# The user:group to run the daemons with
declare -A user_groups
# Key: Process name
# Value: User:Group
# Skipped entries will be set to 0:0 by default
arguments['service1']='1000:1000'

declare -A stop_signals
# Key: Process name
# Value: Stop signal
# Skipped entries will be set to TERM by default
stop_signals['service1']='INT'

# Set skipped arguments entries to ''
for process_name in "${!daemons[@]}"; do
	if [[ ! -v arguments[process_name] ]]; then
		arguments["$process_name"]=''
	fi
done

# Set skipped forking entries to 0
for process_name in "${!daemons[@]}"; do
	if [[ ! -v forking[process_name] ]]; then
		forking["$process_name"]=0
	fi
done

# Set skipped arguments entries to ''
for process_name in "${!daemons[@]}"; do
	if [[ ! -v user_groups[process_name] ]]; then
		user_groups["$process_name"]='0:0'
	fi
done

# Set skipped stop_signals entries to TERM
for process_name in "${!daemons[@]}"; do
	if [[ ! -v stop_signals[process_name] ]]; then
		stop_signals["$process_name"]='TERM'
	fi
done

# Guard agains repeated attempts to stop daemons
STOPPING_DAEMONS=0

# Stops all daemons
stop_daemons() {
	if [ $STOPPING_DAEMONS -ne 0 ]; then
		return 1
	fi
	STOPPING_DAEMONS=1

	local to_skip="$1"
	if [[ "$to_skip" == '--exit' ]]; then
		to_skip=''
	fi

	echo "Stopping daemons..."
	local exit_code=0
	local result=0

	declare -A pids

	# Send the stop signal to the daemons
	for process_name in "${!daemons[@]}"; do
		if [[ "$process_name" == "$to_Skip" ]]; then
			continue
		fi

		start-stop-daemon --stop --quiet --name "$process_name" --signal stop_signals["$process_name"] &>/proc/self/fd/1 &
		pids["$process_name"]=($!)
	done

	# Wait for the daemons to exit and check the exit codes
	for process_name in "${!pids[@]}"; do
		pid=${pids["$process_name"]}

		wait $pid
		result=$?

		if [[ $result -eq 0 ]]; then
			echo 1>&2 "Daemon '$process_name' stopped"
		else
			echo 1>&2 "Error: Daemon '$process_name' stopped ($result)"
			exit_code=$result
		fi
	done

	echo "Daemons stopped."

	STOPPING_DAEMONS=0

	if [[ "$1" == '--exit' ]]; then
		exit $exit_code
	else
		return $exit_code
	fi
}

# Stop all daemons in TERM and INT signals
trap 'stop_daemons --exit' SIGTERM SIGINT

# Sleep for the total duration in small intervals to allow the trap to respond to signals
half_sleep() {
	local total_sleep_time=$1
	local sleep_interval=${2:-1}
	local elapsed_time=0

	while [[ $elapsed_time -lt $total_sleep_time ]]; do
		sleep $sleep_interval
		elapsed_time=$((elapsed_time + sleep_interval))
	done
}

# Get the status of a daemon
get_daemon_status() {
	process_name="$1"

	start-stop-daemon \
		--status --quiet \
		--name "$process_name"

	return $?
}

# Start a daemon
start_daemon() {
	process_name="$1"

	local other_args=''
	if [[ ${forking["$process_name"]} -eq 0 ]]; then
		other_args="$other_args --background --output /proc/self/fd/1"
	fi
	if [[ ${user_groups["$process_name"]} != '0:0' ]]; then
		other_args="$other_args --chuid ${user_groups["$process_name"]}"
	fi

	start-stop-daemon \
		--start --quiet \
		$other_args \
		--name "$process_name" \
		--exec "${daemons["$process_name"]}" \
		-- ${arguments["$process_name"]}
	local result=$?

	if [[ $result -eq 0 ]]; then
		echo "Daemon '$process_name' started"
	else
		echo 1>&2 "Error: Daemon '$process_name' failed to start ($result)"
	fi

	return $result
}

# Stop a daemon
stop_daemon() {
	process_name="$1"
	stop_signal="${stop_signals["$process_name"]}"

	start-stop-daemon \
		--stop --quiet \
		--name "$process_name" \
		--signal "$stop_signal"/10/KILL/10
	local result=$?

	if [[ $result -eq 0 ]]; then
		echo "Daemon '$process_name' stopped"
	else
		echo 1>&2 "Error: Daemon '$process_name' stopped ($result)"
	fi

	return $result
}

# Start daemons
for process_name in "${!daemons[@]}"; do
	start_daemon "$process_name"
done

# Wait a bit for the daemons to start
half_sleep 10

# Monitor for the daemon statuses and restarting them if necessary
while true; do
	INTERVAL=60

	# Check daemon statuses
	for process_name in "${!daemons[@]}"; do
		# Skip if stop initiated
		if [[ $STOPPING_DAEMONS -ne 0 ]]; then
			break
		fi

		if [[ ! get_daemon_status "$process_name" ]]; then
			echo 1>&2 "Error: Daemon '$process_name' stopped unexpectedly ($?)"

			# Restart the stopped daemon
			echo "Restarting '$process_name' daemon"
			start_daemon "$process_name"

			INTERVAL=10
		fi
	done

	half_sleep $INTERVAL
done