Creating a Public NAT Gateway

Scenarios

a public NAT gateway to enable your servers to access the Internet or provide services accessible from the Internet.

Notes and Constraints

Rules on one public NAT gateway can use the same EIP, but rules on different NAT gateways must use different EIPs.
Each VPC can be associated with multiple public NAT gateways.
SNAT and DNAT rules can use the same EIP to save resources. However, when Port Type of a DNAT rule is set to All ports, the resource in the DNAT rule will preferentially use all ports of the EIP. So an SNAT rule cannot share an EIP with such a DNAT rule.
If both an EIP and a public NAT gateway are configured for a server, data will be forwarded through the EIP.

Prerequisites

The VPC and subnet where your public NAT gateway will be deployed are available.
To allow traffic to pass through the public NAT gateway, a route to the public NAT gateway in the VPC is required. When you create a public NAT gateway, a default route 0.0.0.0/0 to the public NAT gateway is automatically added to the default route table of the VPC. If the default route 0.0.0.0/0 already exists in the default route table of the VPC before you create the public NAT gateway, the default route that points to the public NAT gateway will fail to be added automatically. In this case, perform the following operations after the public NAT gateway is successfully created: Manually add a different route that points to the gateway or create a default route 0.0.0.0/0 pointing to the gateway in the new routing table.

Procedure

Log in to the management console.
In the upper left corner of the page, click to expand the service list and choose Network > NAT Gateway.
The Public NAT Gateways page is displayed.
On the displayed page, click Public NAT Gateway.

Configure required parameters. For details, see Table 1.

**Table 1** Descriptions of public NAT gateway parameters
Parameter	Description
Region	The region where the public NAT gateway is located.
Specifications	The specifications of the public NAT gateway. The value can be Small, Medium, Large, or Extra-large. You can click Learn more on the page to view details of each specification.
Name	The name of the public NAT gateway. Enter up to 64 characters. Only letters, digits, underscores (_), hyphens (-), and periods (.) are allowed.
VPC	The VPC that the public NAT gateway belongs to. The selected VPC cannot be changed after the public NAT gateway is created. NOTE: To allow traffic to pass through the public NAT gateway, a route to the public NAT gateway in the VPC is required. When you create a public NAT gateway, a default route 0.0.0.0/0 to the public NAT gateway is automatically added to the default route table of the VPC. If the default route 0.0.0.0/0 already exists in the default route table of the VPC before you create the public NAT gateway, the default route that points to the public NAT gateway will fail to be added automatically. In this case, perform the following operations after the public NAT gateway is successfully create: Manually add a different route that points to the gateway or create a default route 0.0.0.0/0 pointing to the gateway in the new routing table.
Subnet	The subnet that the public NAT gateway belongs to. The subnet must have at least one available IP address. The selected subnet cannot be changed after the public NAT gateway is created. The NAT gateway will be deployed in the selected subnet. The NAT gateway works for the entire VPC where it is deployed. To enable communications over the Internet, add SNAT or DNAT rules.
Advanced Settings (Optional)	Click the drop-down arrow to configure advanced parameters of the public NAT gateway, such as Description.
Description	Supplementary information about the public NAT gateway. Enter up to 255 characters. Angle brackets (<>) are not allowed.

Click Create Now. On the page displayed, confirm the public NAT gateway specifications.
Click Submit.
It takes 1 to 5 minutes to create a public NAT gateway.
In the public NAT gateway list, you can see the gateway status.

After the public NAT gateway is created, check whether a default route (0.0.0.0/0) that points to the public NAT gateway exists in the default route table of the VPC where the public NAT gateway is. If no, add a route pointing to the public NAT gateway to the default route table, alternatively, create a custom route table and add the default route 0.0.0.0/0 pointing to the public NAT gateway to the table.

FAQ

What Should I Do If the Number of NAT Gateway Connections Exceeds the Upper Limit?

If the number of requests exceeds the maximum allowed connections of a public NAT gateway, services will be adversely affected. To avoid this situation, create alarm rules on the Cloud Eye console to monitor the number of SNAT connections.
If the number of requests exceeds the maximum allowed connections of a NAT gateway, you are advised to update the NAT gateway by referring to Managing Public NAT Gateways.

Does Changing NAT Gateway Specifications Interrupt Services?

Using a public NAT gateway of more robust specifications does not affect services, but if you switch to a public NAT gateway of less robust specifications, ensure that its capacity can still be enough to meet your service requirements.

Parent topic: Public NAT Gateways

Previous topic: Overview of Public NAT Gateways

Next topic: Managing Public NAT Gateways