$ cd ~/.ssh
$ ssh-keygen -t rsa -f sample
$ ls ~/.ssh | grep sample
sample
sample.pub

$ terraform apply

An execution plan has been generated and is shown below.
Resource actions are indicated with the following symbols:
  + create

Terraform will perform the following actions:
...
Plan: 19 to add, 0 to change, 0 to destroy.

Changes to Outputs:
  + public_ip    = (known after apply)
  + rds_endpoint = (known after apply)

Do you want to perform these actions?
  Terraform will perform the actions described above.
  Only 'yes' will be accepted to approve.

  Enter a value: yes

Apply complete! Resources: 0 added, 0 changed, 0 destroyed.

Outputs:

ec2_endpoint = "ec2-*-***-**-**.ap-northeast-1.compute.amazonaws.com"
rds_endpoint = "terraform-********************.***********.ap-northeast-1.rds.amazonaws.com:3306"```

$ ssh -i ~/.ssh/sample ec2-user@ec2-*-***-**-**.ap-northeast-1.compute.amazonaws.com
...

       __|  __|_  )
       _|  (     /   Amazon Linux 2 AMI
      ___|\___|___|

https://aws.amazon.com/amazon-linux-2/
11 package(s) needed for security, out of 35 available
Run "sudo yum update" to apply all updates.
[ec2-user@ip-10-0-1-8 ~]$

[ec2-user@ip-10-0-1-8 ~]$ sudo yum install -y mysql
[ec2-user@ip-10-0-1-8 ~]$ mysql -h terraform-********************.***********.ap-northeast-1.rds.amazonaws.com -u foo -p
Enter password: 
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MySQL connection id is 14
Server version: 5.7.33 Source distribution

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MySQL [(none)]>