Connect to an EC2 instance running MySQL from another EC2 instance

Question

It takes several minutes for a newly deployed version to ElasticBeanstalk to become available, so I am hoping that someone can spare me all the testing/experimenting :-)

Scenario 1: I need to connect to an EC2 instance running MySQL from another EC2 instance but belonging to a different security group. Do I use the public DNS or the private IP to specify the MySQL host?

Scenario 2: Same as above except both instances belong to the same security group. I believe that I need to use the private IP in this case, correct? Would the public DNS also work?

Thank you!

Ryan · Accepted Answer · 2013-07-08 13:36:30Z

1

You should always use the private IP when possible for ec2 instances communicating with each other.

Among other reasons, you will get charged money for using the public ip even though the machines are started in the same availability zone.

Also, the security group is just a set of inbound and outbound rules, it doesn't matter that the two machines are in different groups with different rules so long as your mysql server can accept traffic on the port from the other ec2 instance based on the ruleset.

If you're going to be starting and stopping instances frequently, you might benefit from creating an elastic IP and attaching it to instances as needed instead of constantly changing configuration files.

answered Jul 8, 2013 at 13:36

Ryan

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