There is issue with this lab. I created two containers for mysql and web app both checks were completed successfully. I could not however connect to database from web-app.
In description is as well one missing information which port should be mapped to host. I used first 80 and then there was no response from app. So I deleted container and created one with 8080.
Afterwards I got red page that connection is not working.
Additionally check should not be successull when wrong port is mapped for webapp.
kindly check the solution below as it works fine: