"Bern": Docker web container can't connect to db container. fails to recognise working solution

[joshuamkite]

docker network create wordpress_net
docker network connect wordpress_net wordpress
docker network connect wordpress_net mariadb
5d9697c2a030a4469c2dedbe8be0541d4022a6545c036fa42a335be319dc05bf
root@ip-172-31-19-232:~# docker exec wordpress mysqladmin -h mariadb -u root -ppassword ping
mysqld is alive
root@ip-172-31-19-232:~# exit
admin@ip-172-31-19-232:/$ cat ~/agent/check.sh
#!/usr/bin/bash
res=$(sudo docker exec wordpress mysqladmin -h mysql -u root -ppassword --connect-timeout 2 ping)
res=$(echo $res|tr -d '\r')

if [[ "$res" = "mysqld is alive" ]]
then
  echo -n "OK"
else
  echo -n "NO"
fi

admin@ip-172-31-19-232:/$ ~/agent/check.sh
mysqladmin: connect to server at 'mysql' failed
error: 'Unknown MySQL server host 'mysql' (-2)'
Check that mysqld is running on mysql and that the port is 3306.
You can check this by doing 'telnet mysql 3306'