AWS Certified SysOps Administrator Practice Exam

What could be a reason for a website displaying "512 - Cannot connect to the database"?

1. EC2 instance running out of CPU

2. DB Security Group inbound rules have changed

3. RDS instance being terminated

4. Network bandwidth limits exceeded

The correct answer is: DB Security Group inbound rules have changed

When a website displays "512 - Cannot connect to the database," it generally indicates that the application server is unable to communicate with the database server. One specific reason for this situation is that the inbound rules for the database's security group have been altered. In AWS, security groups function as virtual firewalls for your instances, controlling inbound and outbound traffic. If the inbound rules for the database's security group have changed and no longer allow traffic from the application server's security group or IP address, the application would be blocked from making a connection to the database. This misconfiguration is a common cause of connection issues between an application and its database. Connective issues related to other factors—such as the CPU usage of an EC2 instance, the termination of an RDS instance, or exceeded network bandwidth limits—may also affect the application’s overall performance, but they are less direct causes of a "Cannot connect to the database" error. For instance, while an EC2 instance running out of CPU could lead to application performance degradation, it wouldn't specifically generate a database connection error unless the application was unable to perform any operations at all. Similarly, a terminated RDS instance would likely result in an entirely different error message, and network bandwidth limits would typically impact