DNS Lookup in php with docker - php

Question

I'm trying to make a program, that are able to DNS Lookup a website, it works fine. Now i wan't to run it in docker, but when try to dns lookup a website, i don't get any output.
<title>DNS LOOKUP</title>
<header>
<p>Do a DNS Lookup on any website!</p>
</header>
<form method="post" action="?action">
<input type="text" name="Host" placeholder="Host" />
<input type="submit" value="DNS Lookup" />
</form>
<?php
if(isset($_GET['action']))
{
$host = $_POST['Host'];
$command = shell_exec("nslookup $host");
}
echo $command;
?>
Docker Compose file:
version: '2'
services:
lookup:
build: .
ports:
- '8888:80'
stdin_open: true
tty: true
volumes:
- ./source:/var/www/html
- ./logs:/var/log/apache2
Docker File:
FROM ubuntu:16.04
RUN apt update
RUN apt install -y \
apache2 \
php \
libapache2-mod-php \
dnsutils
RUN useradd -d /home/chal/ -m -s /bin/nologin chal
WORKDIR /home/chal
COPY source .
USER chal
ENTRYPOINT service apache2 start && /bin/bash