[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-failure

; User and group the process will run as.
User=www-data
Group=www-data

; Letsencrypt-issued certificates will be written to this directory.
Environment=HOME=/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=/var/tmp
ExecReload=/bin/kill -USR1 $MAINPID

; 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

; Drop all other capabilities. Important if you run caddy as privileged user (which you should not).
CapabilityBoundingSet=CAP_NET_BIND_SERVICE
; … but permit caddy to open ports reserved for system services.
;   This could be redundant here, but is needed in case caddy runs as nobody:nogroup.
AmbientCapabilities=CAP_NET_BIND_SERVICE
; … and prevent gaining any new privileges.
NoNewPrivileges=true

; Caveat: Some plugins need additional capabilities. Add them to both above lines.
; - plugin "upload" needs: CAP_LEASE

[Install]
WantedBy=multi-user.target