Scenarios for network interfaces - Amazon Elastic Compute Cloud
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Scenarios for network interfaces

Attaching multiple network interfaces to an instance is useful when you want to:

  • Create a management network.

  • Use network and security appliances in your VPC.

  • Create dual-homed instances with workloads/roles on distinct subnets.

  • Create a low-budget, high-availability solution.

Create a management network

You can create a management network using network interfaces. In this scenario, as illustrated in the following image:

  • The primary network interface (eth0) on the instance handles public traffic.

  • The secondary network interface (eth1) handles backend management traffic, and is connected to a separate subnet in your VPC that has more restrictive access controls.

The public interface, which may or may not be behind a load balancer, has an associated security group that allows access to the server from the internet (for example, allow TCP port 80 and 443 from, or from the load balancer).

The private facing interface has an associated security group allowing SSH access only from an allowed range of IP addresses, either within the VPC, or from the internet, a private subnet within the VPC, or a virtual private gateway.

To ensure failover capabilities, consider using a secondary private IPv4 for incoming traffic on a network interface. In the event of an instance failure, you can move the interface and/or secondary private IPv4 address to a standby instance.

					Creating a management network

Use network and security appliances in your VPC

Some network and security appliances, such as load balancers, network address translation (NAT) servers, and proxy servers prefer to be configured with multiple network interfaces. You can create and attach secondary network interfaces to instances that are running these types of applications and configure the additional interfaces with their own public and private IP addresses, security groups, and source/destination checking.

Creating dual-homed instances with workloads/roles on distinct subnets

You can place a network interface on each of your web servers that connects to a mid-tier network where an application server resides. The application server can also be dual-homed to a backend network (subnet) where the database server resides. Instead of routing network packets through the dual-homed instances, each dual-homed instance receives and processes requests on the front end, initiates a connection to the backend, and then sends requests to the servers on the backend network.

Create a low budget high availability solution

If one of your instances serving a particular function fails, its network interface can be attached to a replacement or hot standby instance pre-configured for the same role in order to rapidly recover the service. For example, you can use a network interface as your primary or secondary network interface to a critical service such as a database instance or a NAT instance. If the instance fails, you (or more likely, the code running on your behalf) can attach the network interface to a hot standby instance. Because the interface maintains its private IP addresses, Elastic IP addresses, and MAC address, network traffic begins flowing to the standby instance as soon as you attach the network interface to the replacement instance. Users experience a brief loss of connectivity between the time the instance fails and the time that the network interface is attached to the standby instance, but no changes to the route table or your DNS server are required.