caddy-installer.sh/etc/systemd/system/caddy.service

[Unit]
Description=Caddy HTTP/2 web server
Documentation=https://caddyserver.com/docs
After=network-online.target
Wants=network-online.target systemd-networkd-wait-online.service

[Service]
# Restart on crash (bad signal), but not on 'clean' failure (error exit code)
# Allow up to 3 restarts within 10 seconds
# (it's unlikely that a user or properly-running script will do this)
Restart=on-abnormal
StartLimitInterval=10
StartLimitBurst=3

# User and group the process will run as
# (www-data is the de facto standard on most systems)
User=www-data
Group=www-data

# Letsencrypt-issued certificates will be written to this directory.
Environment=CADDYPATH=/etc/ssl/caddy

# Always set "-root" to something safe in case it gets forgotten in the Caddyfile.
WorkingDirectory=/etc/ssl/caddy
ExecStart=/usr/local/bin/caddy -log stdout -agree=true -conf=/etc/caddy/Caddyfile -root=/var/tmp
ExecReload=/bin/kill -USR1 $MAINPID

# Limit the number of file descriptors and processes; see `man systemd.exec` for more limit settings.
# Unmodified caddy is not expected to use more than this.
LimitNOFILE=1048576
LimitNPROC=64

# Use private /tmp and /var/tmp, which are discarded after caddy stops.
PrivateTmp=true
# Use a minimal /dev
PrivateDevices=true
# Hide /home, /root, and /run/user. Nobody will steal your SSH-keys.
ProtectHome=true
# Make /usr, /boot, /etc and possibly some more folders read-only.
ProtectSystem=full
# … except /etc/ssl/caddy, because we want Letsencrypt-certificates there
#   and /var/log/caddy, because we want a place where logs can go.
#   This merely retains r/w access rights, it does not add any new. Must still be writable on the host!
ReadWriteDirectories=/etc/ssl/caddy /var/log/caddy

# Note: in v231 and above ReadWritePaths has been renamed to ReadWriteDirectories
; ReadWritePaths=/etc/ssl/caddy /var/log/caddy

# The following additional security directives only work with systemd v229 or later.
# They further retrict privileges that can be gained by caddy.
# Note that you may have to add capabilities required by any plugins in use.
CapabilityBoundingSet=CAP_NET_BIND_SERVICE
AmbientCapabilities=CAP_NET_BIND_SERVICE
NoNewPrivileges=true

# Caveat: Some plugins need additional capabilities.
# For example "upload" needs CAP_LEASE
; CapabilityBoundingSet=CAP_NET_BIND_SERVICE CAP_LEASE
; AmbientCapabilities=CAP_NET_BIND_SERVICE CAP_LEASE
; NoNewPrivileges=true

[Install]
WantedBy=multi-user.target