Systemd Caddy service setup

caddy.service

[Service]
Restart=on-failure
StartLimitInterval=86400
StartLimitBurst=5

; User and group the process will run as.
User=root
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.
ExecStart=/usr/local/bin/caddy -log stdout -agree=true -conf=/etc/caddy/Caddyfile -root=/opt/caddy
ExecReload=/bin/kill -USR1 $MAINPID

; Use graceful shutdown with a reasonable timeout
KillMode=mixed
KillSignal=SIGQUIT
TimeoutStopSec=5s

; Limit the number of file descriptors; see `man systemd.exec` for more limit settings.
LimitNOFILE=1048576
; Unmodified caddy is not expected to use more than that.
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.
;   This merely retains r/w access rights, it does not add any new. Must still be writable on the host!
ReadWriteDirectories=/etc/ssl/caddy

; The following additional security directives only work with systemd v229 or later.
; They further retrict privileges that can be gained by caddy. Uncomment if you like.
; 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

[Install]
WantedBy=multi-user.target