nginx_dns_proxy.sh

#!/bin/bash

if [ "$EUID" -ne 0 ]
  then echo "Me wants sudo!"
  exit
fi
echo "
**************************************************************************************
This script will try to compile and setup nginx as a dns load balancer.

Will do the following:
* check if deb-src is enabled for the main distro repository
* check which nginx version can be installed from the debian
* install nginx build dependencies
* download the nginx source with the same version and compile with stream module.
* offer to overwrite the config for systemd and nginx.conf
**************************************************************************************
"
read -p "Are you sure you want to continue? y/N " -n 1 -r
if [[ !($REPLY =~ ^[Yy]$) ]]
then
    exit
fi

distro_codename=$(dpkg --status tzdata | grep Provides | cut -f2 -d'-')
prefix="/etc/nginx"
nginx_conf_path="/etc/nginx/nginx.conf"
systemd_unit_path="/etc/systemd/system/nginx.service"
temp_dir=$(mktemp)
debian_src_repo="/etc/apt/sources.list.d/$distro_codename-src.list"

update_systemd_unit () {
    echo "[Unit]"                                                           >> $systemd_unit_path
    echo "Description=nginx - high performance web server"                  >> $systemd_unit_path
    echo "Documentation=https://nginx.org/en/docs/"                         >> $systemd_unit_path
    echo "After=network-online.target remote-fs.target nss-lookup.target"   >> $systemd_unit_path
    echo "Wants=network-online.target"                                      >> $systemd_unit_path
    echo ""                                                                 >> $systemd_unit_path
    echo "[Service]"                                                        >> $systemd_unit_path
    echo "Type=forking"                                                     >> $systemd_unit_path
    echo "PIDFile=/var/run/nginx.pid"                                       >> $systemd_unit_path
    echo "ExecStartPre=/usr/sbin/nginx -t -c $nginx_conf_path"              >> $systemd_unit_path
    echo "ExecStart=/usr/sbin/nginx -c $nginx_conf_path"                    >> $systemd_unit_path
    echo "ExecReload=/bin/kill -s HUP \$MAINPID"                            >> $systemd_unit_path
    echo "ExecStop=/bin/kill -s TERM \$MAINPID"                             >> $systemd_unit_path
    echo ""                                                                 >> $systemd_unit_path
    echo "[Install]"                                                        >> $systemd_unit_path
    echo "WantedBy=multi-user.target"                                       >> $systemd_unit_path
}

update_nginx_config () {
    echo "user  www-data;"                                  >> $nginx_conf_path
    echo "worker_processes  $(nproc --all);"                >> $nginx_conf_path
    echo ""                                                 >> $nginx_conf_path
    echo "error_log logs/error.log;"                        >> $nginx_conf_path
    echo "error_log off;"                                   >> $nginx_conf_path
    echo ""                                                 >> $nginx_conf_path
    echo "events {"                                         >> $nginx_conf_path
    echo "    worker_connections 1024;"                     >> $nginx_conf_path
    echo "}"                                                >> $nginx_conf_path
    echo ""                                                 >> $nginx_conf_path
    echo "stream {"                                         >> $nginx_conf_path
    echo "    upstream dns_servers {"                       >> $nginx_conf_path
    echo "        server 192.168.999.999:53;"               >> $nginx_conf_path
    echo "        server 1.1.1.1:53 backup;"                >> $nginx_conf_path
    echo "        server 8.8.8.8:53 backup;"                >> $nginx_conf_path
    echo "    }"                                            >> $nginx_conf_path
    echo ""                                                 >> $nginx_conf_path
    echo "    server {"                                     >> $nginx_conf_path
    echo "        listen 53  udp;"                          >> $nginx_conf_path
    echo "        listen 53; #tcp"                          >> $nginx_conf_path
    echo "        proxy_pass dns_servers;"                  >> $nginx_conf_path
    echo "        proxy_responses 1;"                       >> $nginx_conf_path
    echo "        proxy_timeout 1s;"                        >> $nginx_conf_path
    echo "        # enable for debugging only"              >> $nginx_conf_path
    echo "        #error_log  /var/log/nginx.dns.log info;" >> $nginx_conf_path
    echo "    }"                                            >> $nginx_conf_path
    echo "}"                                                >> $nginx_conf_path
}

# distro main src repo not found
if [[ ! -f $debian_src_repo && -z $(cat /etc/apt/sources.list | grep "deb-src http.* $distro_codename main") ]]
then
    # search for the dist main repo
    if [[ -n $(cat /etc/apt/sources.list | grep "deb http.* $distro_codename main") ]]
    then
        echo $(cat /etc/apt/sources.list | grep "$distro_codename main" | sed 's/deb http/deb-src http/g') >> $debian_src_repo
    # not found, will exit now
    else
        echo -e "\e[31m Error: Can't find the main repository for $distro_codename. Bye Bye"
        exit
    fi
fi


apt update

# get version
ngx_version=$(apt-cache policy nginx | grep Candidate | awk -F ':' '{print $2}' | awk -F '-' '{print $1}' | awk '{ gsub(/ /,""); print }')

# install dependencies
apt build-dep nginx

# get nginx source
cd $temp_dir
wget "https://nginx.org/download/nginx-$ngx_version.tar.gz"
tar zxvf nginx-$ngx_version.tar.gz
cd nginx-$ngx_version

# configure, make and install
./configure --prefix=$prefix \
            --sbin-path=/usr/sbin/nginx \
            --conf-path=$nginx_conf_path \
            --error-log-path=/var/log/nginx/error.log \
            --pid-path=/var/run/nginx.pid \
            --lock-path=/var/run/nginx.lock \
            --user=nginx \
            --group=nginx \
            --build=Debian \
            --with-stream

make
make install

if [[ ! -f $nginx_conf_path ]]
then
    mkdir $prefix
    update_nginx_config
else
    echo ""
    echo "nginx already exists in $nginx_conf_path"
    read -p "Overwrite? y/N" -n 1 -r
    echo ""
    if [[ $REPLY =~ ^[Yy]$ ]]
    then
        echo "" > $nginx_conf_path
        update_nginx_config
    fi
fi


if [ ! -f $systemd_unit_path ];
then
    update_systemd_unit
else
    echo ""
    echo "Systemd unit for nginx already exists"
    read -p "Overwrite? y/N" -n 1 -r
    echo
    if [[ $REPLY =~ ^[Yy]$ ]]
    then
        echo "" > $nginx_conf_path
        update_nginx_config
    fi
fi

## enable and start
systemctl enable 'nginx.service'
systemctl restart 'nginx.service'