Which of the following is the MOST likely cause of the error?

An administrator is creating new severs in a public cloud. The workflow creates and application group with three VMs, one web server, one application server and one database server. The three VMs are all accessible via SSH, but the websites shows a 503-error referring to a database issue.

Which of the following is the MOST likely cause of the error?
A . Misconfigured VLAN
B . Misconfigured proxy
C . Misconfigured firewall rule
D . Misconfigure routing

Answer: D

Explanation:

Reference: https://support.microsoft.com/en-us/help/4464854/scenario-5-my-website-is-throwing-http-error-503-the-service-is-unavai