What should a database specialist do to resolve this issue?
Create a second security group on the EC2 instances. Add an outbound rule to allow traffic from the ElastiCache cluster security group.
Delete the ElastiCache security group. Add an interface VPC endpoint to enable the EC2 instances to connect to the ElastiCache cluster.
Modify the ElastiCache security group by adding outbound rules that allow traffic to VPC_B’s CIDR blocks from the ElastiCache cluster.
Modify the ElastiCache security group by adding an inbound rule that allows traffic from the EC2 instances’ security group to the ElastiCache cluster.
Explanations:
The security group on the EC2 instances controls inbound traffic, not outbound. Since the EC2 instances are in VPC_B and need to access the ElastiCache cluster in VPC_B, modifying outbound rules on the EC2 instances will not resolve the issue.
An interface VPC endpoint is not required for ElastiCache access. ElastiCache does not use VPC endpoints for access; it requires the correct security group settings for inbound and outbound traffic.
The ElastiCache security group only needs inbound rules to allow traffic from the EC2 instances. Outbound rules are generally not needed unless there’s a specific requirement for returning traffic.
The correct solution is to modify the ElastiCache security group by adding an inbound rule that allows traffic from the EC2 instances’ security group to the ElastiCache cluster. This ensures the EC2 instances in VPC_B can access the ElastiCache cluster in VPC_B.
In my experience, the answer is:
Modify the ElastiCache security group by adding an inbound rule that allows traffic from the EC2 instances’ security group to the ElastiCache cluster.