"Possible Source of Application Timeout with EC2-Hosted Front End and RDS Databases in VPC"
Question
An application consists of a front end hosted on EC2 instances in a public VPC subnet and RDS databases in a private VPC subnet.When attempting to establish a connection to the database, the application times out.
What could be the source of this problem?
Answers
Explanations
Click on the arrows to vote for the correct answer
A. B. C. D.Answer: C.
Option A is incorrect because VPC peering is used to establish a secure connection between two VPC's, not subnets.
Option B is incorrect because if database credentials were incorrect, the application would not time out.
The database would return an error code immediately upon establishing a connection.
The question specifically states that there is an issue establishing a connection.
Option C is CORRECT because VPC NSG's on the RDS database subnet must be configured to allow inbound traffic from the public subnet on the database port.
Option D is incorrect because Internet Gateway is used in public subnets to route outbound traffic to the internet.
Reference:
https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Overview.RDSSecurityGroups.htmlThe problem could be caused by several factors. Here are the possible causes and their explanations:
A. VPC Peering is not configured properly: If VPC peering is not set up correctly, the EC2 instances in the public subnet will not be able to communicate with the RDS databases in the private subnet. VPC peering allows communication between two VPCs using private IP addresses. If VPC peering is not properly configured, the traffic from EC2 instances may not reach the RDS databases, resulting in a timeout error.
B. Database credentials are incorrect: If the database credentials provided by the application are incorrect, the application will not be able to connect to the database. The error message will be a timeout, indicating that the database is not responding.
C. Database NSG is not configured to allow traffic from EC2 instances: If the security group associated with the RDS databases is not configured to allow traffic from the EC2 instances in the public subnet, the application will not be able to establish a connection to the database. The error message will be a timeout, indicating that the database is not responding.
D. The public subnet does not have an Internet Gateway configured: If the public subnet in which the EC2 instances are hosted does not have an internet gateway attached, the instances will not be able to communicate with the internet or with resources outside the VPC. This may prevent the application from reaching the RDS databases hosted in the private subnet.
To troubleshoot the issue, you can try the following steps:
Check the VPC peering configuration to ensure that it is set up correctly. You can check the route tables and security group rules to ensure that traffic is allowed between the subnets.
Verify that the database credentials provided by the application are correct. You can do this by checking the application code or by attempting to connect to the database manually using the credentials.
Check the security group associated with the RDS databases to ensure that it is configured to allow traffic from the EC2 instances in the public subnet.
Verify that the public subnet in which the EC2 instances are hosted has an internet gateway attached. You can check the route table associated with the subnet to ensure that it has a route to the internet.
By performing these steps, you can identify and resolve the issue preventing the application from connecting to the RDS databases.
