The Partner Solution implements a self-signed certificate on the RD Gateway intances. After deployment, you must install the root certificate on your administrative clients before you configure the RDP client to connect to your RD Gateway instances. The root certificate will automatically be stored as c:\<servername>.cer.

To distribute this file to administrator workstations and install it, follow these steps:

To utilize the Remote Desktop Gateway functionality in an Active Directory environment, a trusted certificate through your private Certificate Authority or a public DNS registrar is required.

To ensure the deployed servers' operating systems and installed applications have the latest Microsoft updates, run Windows Update on each server.

When considering remote administrative access to your environment, it is important to follow the principle of least privilege. This principle refers to users having the fewest possible permissions necessary to perform their job functions. This helps reduce the attack surface of your environment, making it much harder for an adversary to exploit. An attack surface can be defined as the set of exploitable vulnerabilities in your environment, including the network, software, and users who are involved in the ongoing operation of the system.

Following the principle of least privilege, we recommend reducing the attack surface of your environment by exposing the absolute minimal set of ports to the network while also restricting the source network or IP address that will have access to your EC2 instances.

In addition to the functionality that exists in the Microsoft platform, there are several AWS capabilities to help you implement the principle of least privilege, such as subnets, security groups, and trusted ingress CIDR blocks.

Amazon VPC lets you provision a private, isolated section of the AWS Cloud where you can launch AWS resources in a virtual network that you define. With Amazon VPC, you can define a virtual network topology closely resembling a traditional network that you might operate on your own premises. You have complete control over your virtual networking environment, including selection of your own IP address range, creation of subnets, and configuration of route tables and network gateways.

When deploying a Windows-based architecture on the AWS Cloud, we recommend a VPC configuration that supports the following requirements:

This Partner Solution supports these best practices, as illustrated earlier in this guide. For details on the VPC design used in this Partner Solution, see the Quick Start for building a modular and scalable virtual network architecture with Amazon VPC.

A network access control list (ACL) is a set of permissions that can be attached to any network subnet in a VPC to provide stateless filtering of traffic. Network ACLs can be used for inbound or outbound traffic and provide an effective way to blacklist a CIDR block or individual IP addresses. These ACLs can contain ordered rules to allow or deny traffic based on IP protocol, service port, or source or destination IP address. Figure 3 shows the default ACL configuration for a VPC subnet. This configuration is used for the subnets in the Partner Solution architecture.

You may choose to keep the default network ACL configuration, or you may choose to lock it down with more specific rules to restrict traffic between subnets at the network level. For example, you could set a rule that would allow inbound administrative traffic on TCP port 3389 from a specific set of IP addresses. In either case, you’ll also need to implement security group rules to permit access from users connecting to RD Gateways and between tiered groups of EC2 instances.

All EC2 instances are required to belong to one or more security groups. Security groups allow you to set policies to control open ports and provide isolation between application tiers. In a VPC, every instance runs behind a stateful firewall with all ports closed by default. The security group contains rules responsible for opening inbound and outbound ports on that firewall. While security groups act as an instance-level firewall, they can also be associated with multiple instances, providing isolation between application tiers in your environment. For example, you can create a security group for all your web servers that will allow traffic on TCP port 3389, but only from members of the security group containing your RD Gateway servers. This is illustrated in Figure 4.

Notice that inbound connections from the internet are only permitted over TCP port 443 to the RD gateways. The RD Gateways have an Elastic IP address assigned and have direct access to the internet. The remaining Windows instances are deployed into private subnets and are assigned private IP addresses only. Security group rules allow only the RD Gateways to initiate inbound connections for remote administration to TCP port 3389 for instances in the private subnets.

In this architecture, RDP connections are established over HTTPS to the RD Gateway and proxied to backend instances on the standard RDP TCP port 3389. This configuration helps you reduce the attack surface on your Windows-based instances while allowing administrators to establish connections to all your instances through a single gateway.

It’s possible to provide remote administrative access to all your Windows-based instances through one RD Gateway, but we recommend placing gateways in each Availability Zone for redundancy. The Partner Solution implements this best practice, as illustrated in Figure 5.

In an initial RD Gateway configuration, the servers in the public subnet will need an inbound security group rule permitting TCP port 3389 from the administrator’s source IP address or subnet. Windows instances sitting behind the RD Gateway in a private subnet will be in their own isolated tier. For example, a group of web server instances in a private subnet may be associated with their own web tier security group. This security group will need an inbound rule allowing connections from the RD Gateway on TCP port 3389.

Using this architecture, an administrator can use a traditional RDP connection to an RD Gateway to configure the local server. The RD Gateway can also be used as a jump box; that is, when an RDP connection is established to the desktop of the RD Gateway, an administrator can start a new RDP client session to initiate a connection to an instance in a private subnet, as illustrated in Figure 1.

Although this architecture works well for initial administration, it is not recommended for the long term. To further secure connections and reduce the number of RDP sessions required to administer the servers in the private subnets, the inbound rule should be changed to permit TCP port 443, and the RD Gateway service should be installed and configured with an SSL certificate, and connection and authorization policies.

The Partner Solution sets up a standard TCP port 3389 connection from the administrator’s IP address. You’ll need to follow the post-deployment steps to modify the security group for RD Gateway to use a single inbound rule permitting TCP port 443, as illustrated in Figure 2. This modification will allow a Transport Layer Security (TLS) encrypted RDP connection to be proxied through the gateway over TCP port 443 directly to one or more Windows-based instances in private subnets on TCP port 3389. This configuration increases the security of the connection and also prevents the need to initiate an RDP session to the desktop of the RD Gateway.

The RD Gateway role uses Transport Layer Security (TLS) to encrypt communications over the internet between administrators and gateway servers. To support TLS, a valid X.509 SSL certificate must be installed on each RD Gateway. Certificates can be acquired in a number of ways, including:

For smaller test environments, implementing a self-signed certificate is a straightforward process that helps you get up and running quickly. This Partner Solution automatically generates a self-signed certificate for RD Gateway.

However, if you have a large number of varying administrative devices that need to establish a connection to your gateways, we recommend using a public certificate.

For an RDP client to establish a secure connection with an RD Gateway, the following certificate and DNS requirements must be met:

There are various considerations when choosing the right CA to obtain an SSL certificate. For example, a public certificate may be ideal since the issuing CA will be widely trusted by the majority of client devices that need to connect to your gateways. On the other hand, you may choose to utilize your own PKI infrastructure to ensure that only the machines that are part of your organization will trust the issuing CA.

Users must meet specific requirements to connect to RD Gateway instances:

This Partner Solution automatically sets up connection and resource authorization policies.