Network Architecture

The Trusted Research Environment (TRE) network topology is based on hub-spoke. The TRE Core VNET (Azure Virtual Network) is the central hub and each workspace is a spoke.

Azure TRE VNETs are segregated allowing limited traffic between the TRE Core VNET and Workspace VNETs. The security rules are managed by nsg-ws network security group. See workspace network security groups (NSG) further down.

The Core VNET is further divided into subnets.

Subnet	Description
AzureBastionSubnet	A dedicated subnet for Azure Bastion hosts.
AppGwSubnet	Subnet for Azure Application Gateway controlling ingress traffic.
AzureFirewallSubnet	Subnet for Azure Firewall controlling egress traffic.
ResourceProcessorSubnet	Subnet for VMSS used by the Composition Service to host Docker containers to execute Porter bundles that deploys Workspaces.
WebAppSubnet	Subnet for TRE API.
SharedSubnet	Shared Services subnet for all things shared by TRE Core and Workspaces. Such as Source Mirror Shared Service and Package Mirror Shared Service.

All subnets (Core and Workspace subnets) have a default route which directs egress traffic to the Azure Firewall to ensure only explicitly allowed destinations on the Internet to be accessed.

There are a couple of exceptions:

• AzureFirewallSubnet as it hosts the Azure Firewall which routes traffic to the Internet.
• AzureBastionSubnet as it hosts Azure Bastion which is the management jump box within the VNET with Internet access.
• AppGwSubnet as it hosts the Azure Application Gateway which has to be able to a ping the health endpoints e.g. TRE API.

Ingress and egress

Ingress traffic from the Internet is only allowed through the Application Gateway, which forwards HTTPS (port 443) call to the TRE API in the WebAppSubnet.

Egress traffic is routed through the Azure Firewall with a few exceptions and by default all ingress and egress traffic is denied except explicitly allowed.

The explicitly allowed egress traffic is described here:

• Resource Processor
• TRE API
• Gitea Shared Service
• Nexus Shared Service

Azure Monitor

Azure Monitor resources are secured using Azure Monitor Private Link Scope (AMPLS) keeping all traffic inside the Microsoft Azure backbone network. The Azure Monitor resources and their network configuration is defined in /core/terraform/azure-monitor folder and the required private DNS zones in file /core/terraform/network/dns_zones.tf.

Network security groups

TRE Core

Network security groups (NSG), and their security rules for TRE core resources are defined in /core/terraform/network/network_security_groups.tf.

Network security group	Associated subnet(s)
nsg-bastion-subnet	AzureBastionSubnet
nsg-app-gw	AppGwSubnet
nsg-default-rules	ResourceProcessorSubnet, SharedSubnet, WebAppSubnet

Workspaces

Azure TRE VNETs are segregated allowing limited traffic between the TRE Core VNET and Workspace VNETs. The rules to manage and limit the traffic between the TRE Core VNET and Workspace VNETs are defined by the nsg-ws network security group:

• Inbound traffic from TRE Core VNET to workspace allowed for Azure Bastion (22, 3389) - All other inbound traffic from Core to workspace denied.
• Outbound traffic to SharedSubnet from Workspace allowed.
• Outbound traffic to Internet allowed on HTTPS port 443 (next hop Azure Firewall).
• All other outbound traffic denied.

Each of these rules can be managed per workspace.

Caution

In Azure, traffic between subnets are allowed except explicitly denied.