Install Caddy Server (on Debian)

curl https://getcaddy.com | bash -s personal http.git
chown root:root /usr/local/bin/caddy

Create directories & configs:

chmod 755 /usr/local/bin/caddy
touch /etc/caddy/Caddyfile

Prepare Caddy for running

Execute the following command to permit the Caddy’s binary file to listen on preferred port:

apt install libcap2-bin -y # when setcap missing
setcap CAP_NET_BIND_SERVICE=+eip /usr/local/bin/caddy

Create Caddy user:

groupadd caddy
useradd \
-g caddy \
--home-dir /var/www --no-create-home \
--shell /usr/sbin/nologin \
--system caddy

Then, create Caddy's configuration directories and set proper permissions

mkdir /etc/caddy
touch /etc/caddy/Caddyfile
chown -R root:caddy /etc/caddy
chown caddy:caddy /etc/caddy/Caddyfile
chmod 444 /etc/caddy/Caddyfile

Make the SSL directory to store your SSL configurations:

mkdir /etc/ssl/caddy
chown -R caddy:root /etc/ssl/caddy
chmod 770 /etc/ssl/caddy

And create www dir:

mkdir /var/www

Install Caddy as System Service

Crate cadddy.service file: sudo nano /etc/systemd/system/caddy.service with follow contains:

[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
StartLimitInterval=864000
StartLimitBurst=500

; User and group the process will run as.
User=caddy
Group=caddy

; 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=/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

; The following additional security directives only work with systemd v229 or later.
; They further restrict 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

Then, change rights:

chown root:root /etc/systemd/system/caddy.service
chmod 644 /etc/systemd/system/caddy.service

Reload systemctl:

systemctl daemon-reload
systemctl start caddy
systemctl enable caddy
systemctl restart caddy
systemctl status caddy

Upgrade Caddy server

systemctl stop caddy
curl https://getcaddy.com | bash -s personal http.git
systemctl start caddy