Questions[heredoc](server)

What is the proper way to pass variable from one machine to another machine via bash script? In the below code I am trying to get the input from user and want to pass the same to remote machine, but the value is not getting accessed in remote machine, can anyone let me know the proper way to do it?

NEWLINE=$'\n'
read -s -p "Enter App FQDN:${NEWLINE}" APP_FQDN
read -s -p "Enter App Password:${NEWLINE}" APP_PASSWORD
read -s -p "Enter VD Password:${NEWLINE}" VD_PASSWORD
sshpass -p "$APP_PASSWORD" ssh -o StrictHostKeyChecking=no -T root@$APP_FQDN << 'EOSSH'
if true; then
 su - presto << 'PRESTO'
 source ~/.bash_profile
 cd /opt/vm/vchs/presto_agent
 pwd
 KEY=$( cat /opt/vm/vchs/presto_agent/config/settings.yml |grep '^key:'|sed 's/^key: //')
 echo $KEY
 echo $VD_PASSWORD
 PASSWORD=$(ruby /opt/vm/vchs/presto_agent/lib/obfuscation_util.rb encrypt $KEY $VD_PASSWORD)
 echo $PASSWORD
PRESTO
else
 echo "False"
fi
EOSSH

While executing the above script $VD_PASSWORD is echo blanks

I'm working with a bash script trying to stop it from attempting to replace variables inside my heredoc. How do set a heredoc to either A) escape the variable names instead of parsing them or B) return the entire string untouched?

cat > /etc/nginx/sites-available/default_php <<END
server {
    listen 80 default;
    server_name _;
    root /var/www/$host; <--- $host is a problem child
}
END

As is, when I it finishes injecting it into a file I'm left with this:

server {
    listen 80 default;
    server_name _;
    root /var/www/;
}