Fatal error: Uncaught Error: Call to undefined function mysqli_connect()

Error

Fatal error: Uncaught Error: Call to undefined function mysqli_connect() in /var/www/html/login.php:8 Stack trace: #0 {main} thrown in /var/www/html/login.php on line 8

Code

<?php
$servername = "172.17.0.2:3306";
$username = "mysql_user";
$password = "mysql_password";
$dbname = "invoice";

// Create connection
$conn = mysqli_connect($servername, $username, $password,$dbname);
?>

I am running it from php:7.0-apache docker container and I have already installed mysqli extension using following command:

docker-php-ext-install mysqli 
docker-php-ext-enable mysqli
apachectl restart

What did I miss?