Connect to an RDS Custom instance - - Alibaba Cloud Documentation Center

Prerequisites

The RDS Custom instance is running.
You have configured logon credentials, such as a custom password or a key pair, for the RDS Custom instance.

If you use a key pair to connect to the RDS Custom instance, ensure the private key file (.pem) is saved on your local device. For more information, see Create an SSH key pair.

Step 1: Get the IP address

You can connect to an RDS Custom instance by using a private IP address or an Elastic IP Address (EIP).

Connection method	Description	Billing
Private IP address	You can connect to the RDS Custom instance only from an ECS instance in the same region and VPC.	Data transfer is free.
Elastic IP Address (EIP)	You can connect from ECS instances (regardless of the region and VPC), on-premises servers, and common SSH clients such as OpenSSH, PuTTY, and Xshell.	If you enable and use an EIP, you are charged hourly based on the actual data transfer and duration of use. Usage of less than one hour in a billing cycle is billed as one hour. These fees are billed by the EIP service. The billing formula is as follows. The unit price for data transfer varies by region. For specific pricing, refer to the EIP Billing topic. `In a billing cycle: Data Transfer Fee = Unit Price (per GB) × Data Transferred (GB)`

Log on to the RDS console. In the navigation pane on the left, choose RDS Custom > Custom Instances. In the top navigation bar, select a region.
Click the instance ID to go to the instance details page.
On the Basic Information page, in the Configuration Information section, get the private IP address or associate an EIP.

Note
When you associate an EIP, you can select an existing EIP or create a new one. To create an EIP, see Apply for an EIP.

Step 2: (Optional) Configure security group rules

If you connect by using an EIP, you must add your client's public IP address to the security group of the RDS Custom instance. Skip this step if you use a private IP address.

Log on to the RDS console. In the navigation pane on the left, choose RDS Custom > Custom Instances. In the top navigation bar, select a region.
Click the instance ID to go to the instance details page.
On the Basic Information page, in the Other Information section, get the security group ID of the RDS Custom instance.
Log on to the ECS console, find the security group of the RDS Custom instance, and add a security group rule. For more information, see Add a security group rule.

Step 3: Connect to the RDS Custom instance

This section uses an ECS instance to demonstrate how to connect to an RDS Custom instance.

Connect using a custom password

Log on to your ECS instance. For more information, see the Connect to an ECS instance section in Use the console to manage an ECS instance.
Run the following command to connect and enter the password for your RDS Custom instance when prompted.
```
ssh <username>@<ip_address>
```
- <username>: The username for your RDS Custom instance. The default is root.
- <ip_address>: The IP address of your RDS Custom instance.

Warning

After you log on to the RDS Custom instance, avoid modifying the route table, iptables firewall rules, or network interface configurations (including restarting eth0) to prevent connection interruptions.

Connect using a key pair

By command

Log on to your ECS instance. For more information, see the Connect to an ECS instance section in Use the console to manage an ECS instance.
Upload your private key file (.pem) to the ECS instance. For example, you can upload it to the ~/.ssh directory.
Run the following command to change the permissions of the private key file:
```
chmod 400 <path_to_private_key_file.pem>
```
Example:
```
chmod 400 ~/.ssh/custom_test.pem
```

Run the following command to connect to the RDS Custom instance:

ssh -i <path_to_private_key_file.pem> <username>@<ip_address>

Example:

ssh -i ~/.ssh/custom_test.pem root@172.26.XX.XX

By config file

Log on to your ECS instance. For more information, see the Connect to an ECS instance section in Use the console to manage an ECS instance.
Upload your private key file (.pem) to the ECS instance. For example, you can upload it to the ~/.ssh directory.
Run the following command to change the permissions of the private key file:
```
chmod 400 <path_to_private_key_file.pem>
```
Example:
```
chmod 400 ~/.ssh/custom_test.pem
```
Run the following commands to navigate to the .ssh directory in your home directory and then create and edit the config file:
```
cd ~/.ssh
vim config
```

In the config file, press i to enter edit mode, and then add the following configuration:

# An alias for the RDS Custom instance, used for the SSH remote connection.
Host custom_test
# The IP address of the RDS Custom instance.
HostName 172.26.XX.XX
# The port number. The default is 22.
Port 22
# The logon account. The default is root.
User root
# The path to the .pem private key file on your machine.
IdentityFile ~/.ssh/custom_test.pem

Run the following command to restart the SSH service:

Warning
If the SSH service fails to restart, it may become unavailable and interrupt your services. We recommend performing this operation during off-peak hours.
```
service sshd restart
```
Run the following command to connect to the RDS Custom instance:
```
ssh <alias_of_rds_custom_instance>
```
Example:
```
ssh custom_test
```