Issues connecting slave to master instance RDS MYSQL-Aurora

Question

I'm working on setting up MYSQL to Aurora replication between two RDS instance. when I enable the replication, my slave instance is failing to connect to master. By default, the security group(default) of both instances are same since it's a replica.

I was told to allow the IP address of the slave instance to the inbound rules of the master.Since the security group is same, it doesn't make sense to me. Please correct me if I'm wrong or provide your thoughts.

Note: I'm following this documentation http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Aurora.Overview.Replication.MySQLReplication.html

Answer 1

Since the security group is same, it doesn't make sense to me.

Being in the same security group does not mean the two machines can talk to each other. It only means the two machines follow the same set of rules.

To allow a machine in a security group to connect to another machine in the same security group still requires a rule in the security group to allow the access.