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Azure Virtual Network Hub Terraform Module

This module deploys a hub network using the Microsoft recommended Hub-Spoke network topology. Usually, only one hub in each region with multiple spokes and each of them can also be in separate subscriptions.

The following reference architecture shows how to implement a hub-spoke topology in Azure. The hub is a virtual network in Azure that acts as a central point of connectivity to an on-premises network. The spokes are virtual networks that peer with the hub and can be used to isolate workloads. Traffic flows between the on-premises datacenter and the hub through an ExpressRoute or VPN gateway connection.

This is designed to quickly deploy hub and spoke architecture in the azure and further security hardening would be recommend to add appropriate NSG rules to use this for any production workloads.

Source: Microsoft Azure Hub-Spoke Topology Documentation

These types of resources are supported:

• Virtual Network
• Subnets
• Subnet Service Delegation
• Virtual Network service endpoints
• Private Link service/Endpoint network policies on Subnet
• AzureNetwork DDoS Protection Plan
• Network Security Groups
• Role Assignment for Peering
• Storage Account
• Log Analytics Workspace
• Azure Monitoring Diagnostics
• Network Watcher
• Network Watcher Workflow Logs
• Private DNS Zone

Module Usage

module "vnet-hub" {
  source = "github.com/tietoevry-infra-as-code/terraform-azurerm-caf-vnet-hub?ref=v2.0.0"

  # By default, this module will create a resource group, proivde the name here
  # to use an existing resource group, specify the existing resource group name,
  # and set the argument to `create_resource_group = false`. Location will be same as existing RG.
  resource_group_name = "rg-hub-shared-westeurope-002"
  location            = "westeurope"
  hub_vnet_name       = "default-hub"

  # Provide valid VNet Address space and specify valid domain name for Private DNS Zone.  
  vnet_address_space            = ["10.1.0.0/16"]
  gateway_subnet_address_prefix = ["10.1.1.0/27"]
  private_dns_zone_name         = "publiccloud.example.com"

  # (Required) To enable Azure Monitoring and flow logs
  # Log Retention in days - Possible values range between 30 and 730
  log_analytics_workspace_sku          = "PerGB2018"
  log_analytics_logs_retention_in_days = 30

  # Adding Standard DDoS Plan, and custom DNS servers (Optional)
  dns_servers = []

  # Multiple Subnets, Service delegation, Service Endpoints, Network security groups
  # These are default subnets with required configuration, check README.md for more details
  # NSG association to be added automatically for all subnets listed here.
  # First two address ranges from VNet Address space reserved for Gateway And Firewall Subnets.
  # ex.: For 10.1.0.0/16 address space, usable address range start from 10.1.2.0/24 for all subnets.
  # subnet name will be set as per Azure naming convention by defaut. expected value here is: <App or project name>
  subnets = {
    mgnt_subnet = {
      subnet_name           = "management"
      subnet_address_prefix = ["10.1.2.0/24"]
      service_endpoints     = ["Microsoft.Storage"]

      nsg_inbound_rules = [
        # [name, priority, direction, access, protocol, destination_port_range, source_address_prefix, destination_address_prefix]
        # To use defaults, use "" without adding any value and to use this subnet as a source or destination prefix.
        ["ssh", "200", "Inbound", "Allow", "Tcp", "22", "*", ""],
        ["rdp", "201", "Inbound", "Allow", "Tcp", "3389", "*", ""],
      ]
      nsg_outbound_rules = [
        # [name, priority, direction, access, protocol, destination_port_range, source_address_prefix, destination_address_prefix]
        # To use defaults, use "" without adding any value and to use this subnet as a source or destination prefix.
        ["ntp_out", "203", "Outbound", "Allow", "Udp", "123", "", "0.0.0.0/0"],
      ]
    }

    dmz_subnet = {
      subnet_name           = "appgateway"
      subnet_address_prefix = ["10.1.3.0/24"]
      service_endpoints     = ["Microsoft.Storage"]
      nsg_inbound_rules = [
        # [name, priority, direction, access, protocol, destination_port_range, source_address_prefix, destination_address_prefix]
        # To use defaults, use "" without adding any value and to use this subnet as a source or destination prefix.
        ["http", "100", "Inbound", "Allow", "Tcp", "80", "*", "0.0.0.0/0"],
        ["https", "101", "Inbound", "Allow", "Tcp", "443", "*", ""],

      ]
      nsg_outbound_rules = [
        # [name, priority, direction, access, protocol, destination_port_range, source_address_prefix, destination_address_prefix]
        # To use defaults, use "" without adding any value and to use this subnet as a source or destination prefix.
        ["ntp_out", "102", "Outbound", "Allow", "Udp", "123", "", "0.0.0.0/0"],
      ]
    }
  }

  # Adding TAG's to your Azure resources (Required)
  # ProjectName and Env are already declared above, to use them here, create a varible.
  tags = {
    ProjectName  = "demo-internal"
    Env          = "dev"
    Owner        = "user@example.com"
    BusinessUnit = "CORP"
    ServiceClass = "Gold"
  }
}

Create resource group

By default, this module will create a resource group and the name of the resource group to be given in an argument resource_group_name. If you want to use an existing resource group, specify the existing resource group name, and set the argument to create_resource_group = false.

If you are using an existing resource group, then this module uses the same resource group location to create all resources in this module.

Azure Network DDoS Protection Plan

By default, this module will create a DDoS Protection Plan. You can enable/disable it by appending an argument create_ddos_plan. If you want to disable a DDoS plan using this module, set argument create_ddos_plan = false.

Custom DNS servers

This is an optional feature and only applicable if you are using your own DNS servers superseding default DNS services provided by Azure.Set the argument dns_servers = ["4.4.4.4"] to enable this option. For multiple DNS servers, set the argument dns_servers = ["4.4.4.4", "8.8.8.8"]

Subnets

This module handles the creation and a list of address spaces for subnets. This module uses for_each to create subnets and corresponding service endpoints, service delegation, and network security groups. This module associates the subnets to network security groups as well with additional user-defined NSG rules.

This module creates 4 subnets by default: Gateway Subnet, AzureFirewallSubnet, and Management Subnet.

Name	Description
GatewaySubnet	Contain VPN Gateway, Express route Gateway
AzureFirewallSubnet	If added the Firewall module, it Deploys an Azure Firewall that will monitor all incoming and outgoing traffic
ApplicationGateway	Contain an Application Gateway etc...
Management	Management subnet for Bastion host, accessible from gateway

The Gateway Subnet allow traffic out and can have public IPs. ApplicationGateway and Management subnet route traffic through the firewall and does not support public IPs due to asymmetric routing.

Virtual Network service endpoints

Service Endpoints allows connecting certain platform services into virtual networks. With this option, Azure virtual machines can interact with Azure SQL and Azure Storage accounts, as if they’re part of the same virtual network, rather than Azure virtual machines accessing them over the public endpoint.

This module supports enabling the service endpoint of your choosing under the virtual network and with the specified subnet. The list of Service endpoints to associate with the subnet values include: Microsoft.AzureActiveDirectory, Microsoft.AzureCosmosDB, Microsoft.ContainerRegistry, Microsoft.EventHub, Microsoft.KeyVault, Microsoft.ServiceBus, Microsoft.Sql, Microsoft.Storage and Microsoft.Web.

module "vnet-hub" {
  source = "github.com/tietoevry-infra-as-code/terraform-azurerm-caf-vnet-hub?ref=v2.0.0"

  # .... omitted

  # Multiple Subnets, Service delegation, Service Endpoints
  subnets = {
    mgnt_subnet = {
      subnet_name           = "management"
      subnet_address_prefix = "10.1.2.0/24"

      service_endpoints     = ["Microsoft.Storage"]  
    }
  }

# ....omitted

}

Subnet Service Delegation

Subnet delegation enables you to designate a specific subnet for an Azure PaaS service of your choice that needs to be injected into your virtual network. The Subnet delegation provides full control to manage the integration of Azure services into virtual networks.

This module supports enabling the service delegation of your choosing under the virtual network and with the specified subnet. For more information, check the terraform resource documentation.

module "vnet-hub" {
  source = "github.com/tietoevry-infra-as-code/terraform-azurerm-caf-vnet-hub?ref=v2.0.0"

  # .... omitted

  # Multiple Subnets, Service delegation, Service Endpoints
  subnets = {
    mgnt_subnet = {
      subnet_name           = "management"
      subnet_address_prefix = "10.1.2.0/24"

      delegation = {
        name = "demodelegationcg"
        service_delegation = {
          name    = "Microsoft.ContainerInstance/containerGroups"
          actions = ["Microsoft.Network/virtualNetworks/subnets/join/action", "Microsoft.Network/virtualNetworks/subnets/prepareNetworkPolicies/action"]
        }
      }
    }
  }

# ....omitted

}

enforce_private_link_endpoint_network_policies - Private Link Endpoint on the subnet

Network policies, like network security groups (NSG), are not supported for Private Link Endpoints. In order to deploy a Private Link Endpoint on a given subnet, you must set the enforce_private_link_endpoint_network_policies attribute to true. This setting is only applicable for the Private Link Endpoint, for all other resources in the subnet access is controlled based via the Network Security Group which can be configured using the azurerm_subnet_network_security_group_association resource.

This module Enable or Disable network policies for the private link endpoint on the subnet. The default value is false. If you are enabling the Private Link Endpoints on the subnet you shouldn't use Private Link Services as it's conflicts.

module "vnet-hub" {
  source = "github.com/tietoevry-infra-as-code/terraform-azurerm-caf-vnet-hub?ref=v2.0.0"

  # .... omitted

  # Multiple Subnets, Service delegation, Service Endpoints
  subnets = {
    mgnt_subnet = {
      subnet_name           = "management"
      subnet_address_prefix = "10.1.2.0/24"
      enforce_private_link_endpoint_network_policies = true

        }
      }
    }
  }

# ....omitted

}

enforce_private_link_service_network_policies - private link service on the subnet

In order to deploy a Private Link Service on a given subnet, you must set the enforce_private_link_service_network_policies attribute to true. This setting is only applicable for the Private Link Service, for all other resources in the subnet access is controlled based on the Network Security Group which can be configured using the azurerm_subnet_network_security_group_association resource.

This module Enable or Disable network policies for the private link service on the subnet. The default value is false. If you are enabling the Private Link service on the subnet then, you shouldn't use Private Link endpoints as it's conflicts.

module "vnet-hub" {
  source = "github.com/tietoevry-infra-as-code/terraform-azurerm-caf-vnet-hub?ref=v2.0.0"

  # .... omitted

  # Multiple Subnets, Service delegation, Service Endpoints
  subnets = {
    mgnt_subnet = {
      subnet_name           = "management"
      subnet_address_prefix = "10.1.2.0/24"
      enforce_private_link_service_network_policies = true

        }
      }
    }
  }

# ....omitted

}

Network Security Groups

By default, the network security groups connected to Management and ApplicationGateway will only allow necessary traffic and block everything else (deny-all rule). Use nsg_inbound_rules and nsg_outbound_rules in this Terraform module to create a Network Security Group (NSG) for each subnet and allow it to add additional rules for inbound flows.

In the Source and Destination columns, VirtualNetwork, AzureLoadBalancer, and Internet are service tags, rather than IP addresses. In the protocol column, Any encompasses TCP, UDP, and ICMP. When creating a rule, you can specify TCP, UDP, ICMP or *. 0.0.0.0/0 in the Source and Destination columns represents all addresses.

You cannot remove the default rules, but you can override them by creating rules with higher priorities.

module "vnet-hub" {
  source = "github.com/tietoevry-infra-as-code/terraform-azurerm-caf-vnet-hub?ref=v2.0.0"

  # .... omitted
  
  # Multiple Subnets, Service delegation, Service Endpoints
  subnets = {
    mgnt_subnet = {
      subnet_name           = "management"
      subnet_address_prefix = "10.1.2.0/24"

      nsg_inbound_rules = [
        # [name, priority, direction, access, protocol, destination_port_range, source_address_prefix, destination_address_prefix]
        # To use defaults, use "" without adding any value and to use this subnet as a source or destination prefix.
        ["ssh", "200", "Inbound", "Allow", "Tcp", "22", "*", ""],
        ["rdp", "201", "Inbound", "Allow", "Tcp", "3389", "*", ""],
      ]

      nsg_outbound_rules = [
        # [name, priority, direction, access, protocol, destination_port_range, source_address_prefix, destination_address_prefix]
        # To use defaults, use "" without adding any value and to use this subnet as a source or destination prefix.
        ["ntp_out", "203", "Outbound", "Allow", "Udp", "123", "", "0.0.0.0/0"],
      ]
    }
  }
}

Network Watcher

This module handle the provision of Network Watcher resource by defining create_network_watcher variable. It will enable network watcher, flow logs and traffic analytics for all the subnets in the Virtual Network. Since Azure uses a specific naming standard on network watchers, It will create a resource group NetworkWatcherRG and adds the location specific resource.

Azure Monitoring Diagnostics

Platform logs in Azure, including the Azure Activity log and resource logs, provide detailed diagnostic and auditing information for Azure resources and the Azure platform they depend on. Platform metrics are collected by default and typically stored in the Azure Monitor metrics database. This module enables to send all the logs and metrics to either storage account, event hub or Log Analytics workspace.

Peering

To peer spoke networks to the hub networks requires the service principal that performs the peering has Network Contributor role on hub network. Linking the Spoke to Hub DNS zones, the service principal also needs the Private DNS Zone Contributor role on hub network.

Private DNS Zone

This module facilitates the private DNS zone for the virtual network. To create a zone, set the domain name for the private DNS zone with variable private_dns_zone_name. This will additionally link the virtual network hub to the private DNS zone. It will assign all principals that have peering access as contributors so, spokes can remain linked to the same zone.

Recommended naming and tagging conventions

Well-defined naming and metadata tagging conventions help to quickly locate and manage resources. These conventions also help associate cloud usage costs with business teams via chargeback and show back accounting mechanisms.

Resource naming

An effective naming convention assembles resource names by using important resource information as parts of a resource's name. For example, using these recommended naming conventions, a public IP resource for a production SharePoint workload is named like this: pip-sharepoint-prod-westus-001.

Metadata tags

When applying metadata tags to the cloud resources, you can include information about those assets that couldn't be included in the resource name. You can use that information to perform more sophisticated filtering and reporting on resources. This information can be used by IT or business teams to find resources or generate reports about resource usage and billing.

The following list provides the recommended common tags that capture important context and information about resources. Use this list as a starting point to establish your tagging conventions.

Tag Name	Description	Key	Example Value	Required?
Project Name	Name of the Project for the infra is created. This is mandatory to create a resource names.	ProjectName	{Project name}	Yes
Application Name	Name of the application, service, or workload the resource is associated with.	ApplicationName	{app name}	Yes
Approver	Name Person responsible for approving costs related to this resource.	Approver	{email}	Yes
Business Unit	Top-level division of your company that owns the subscription or workload the resource belongs to. In smaller organizations, this may represent a single corporate or shared top-level organizational element.	BusinessUnit	FINANCE, MARKETING,{Product Name},CORP,SHARED	Yes
Cost Center	Accounting cost center associated with this resource.	CostCenter	{number}	Yes
Disaster Recovery	Business criticality of this application, workload, or service.	DR	Mission Critical, Critical, Essential	Yes
Environment	Deployment environment of this application, workload, or service.	Env	Prod, Dev, QA, Stage, Test	Yes
Owner Name	Owner of the application, workload, or service.	Owner	{email}	Yes
Requester Name	User that requested the creation of this application.	Requestor	{email}	Yes
Service Class	Service Level Agreement level of this application, workload, or service.	ServiceClass	Dev, Bronze, Silver, Gold	Yes
Start Date of the project	Date when this application, workload, or service was first deployed.	StartDate	{date}	No
End Date of the Project	Date when this application, workload, or service is planned to be retired.	EndDate	{date}	No

This module allows you to manage the above metadata tags directly or as an variable using variables.tf. All Azure resources which support tagging can be tagged by specifying key-values in argument tags. Tag ResourceName is added automatically to all resources.

module "vnet-hub" {
  source = "github.com/tietoevry-infra-as-code/terraform-azurerm-caf-vnet-hub?ref=v2.0.0"
  create_resource_group   = true

  # ... omitted

  tags = {
    ProjectName  = "demo-internal"
    Env          = "dev"
    Owner        = "user@example.com"
    BusinessUnit = "CORP"
    ServiceClass = "Gold"
  }
}

Requirements

Name	Version
terraform	>= 0.13
azurerm	~> 2.27.0

Providers

Name	Version
azurerm	~> 2.27.0
random	n/a

Inputs

Name	Description	Type	Default
create_resource_group	Whether to create resource group and use it for all networking resources	string	true
resource_group_name	The name of the resource group in which resources are created	string	""
location	The location of the resource group in which resources are created	string	""
gateway_subnet_address_prefix	The address prefix to use for the gateway subnet	list	null
vnet_address_space	Virtual Network address space to be used	list	[]
create_ddos_plan	Controls if DDoS protection plan should be created	string	true
dns_servers	List of DNS servers to use for virtual network	list	[]
subnets	For each subnet, create an object that contain fields	object	{}
subnet_name	A name of subnets inside virtual network	object	{}
subnet_address_prefix	A list of subnets address prefixes inside virtual network
delegation	defines a subnet delegation feature. takes an object as described in the following example	object	{}
service_endpoints	service endpoints for the virtual subnet	object	{}
nsg_inbound_rule	network security groups settings - a NSG is always created for each subnet	object	{}
nsg_outbound_rule	network security groups settings - a NSG is always created for each subnet	object	{}
private_dns_zone_name	The name of the Private DNS Zone. Must be a valid domain name to enable the resource creation	string	""
log_analytics_workspace_sku	The SKU of the Log Analytics Workspace. Possible values are Free, PerNode, Premium, Standard, Standalone, Unlimited, and PerGB2018	string	PerGB2018
log_analytics_logs_retention_in_days	The log analytics workspace data retention in days. Possible values range between 30 and 730	number	30
Tags	A map of tags to add to all resources	map	{}

Outputs

Name	Description
resource_group_name	The name of the resource group in which resources are created
resource_group_id	The id of the resource group in which resources are created
resource_group_location	The location of the resource group in which resources are created
virtual_network_name	The name of the virtual network.
virtual_network_id	The virtual NetworkConfiguration ID.
virtual_network_address_space	List of address spaces that are used the virtual network.
subnet_ids	List of IDs of subnets
subnet_address_prefixes	List of address prefix for subnets
network_security_group_ids	List of Network security groups and ids
ddos_protection_plan_id	Azure Network DDoS protection plan id
network_watcher_id	ID of Network Watcher
private_dns_zone_name	The name of Private DNS zones within Azure DNS
private_dns_zone_id	The resource id of Private DNS zones within Azure DNS
storage_account_id	The ID of the storage account
storage_account_name	The name of the storage account
storage_primary_access_key	The primary access key for the storage account
log_analytics_workspace_name	Specifies the name of the Log Analytics Workspace
log_analytics_workspace_id	The resource id of the Log Analytics Workspace
log_analytics_customer_id	The Workspace (or Customer) ID for the Log Analytics Workspace.
log_analytics_logs_retention_in_days	The log analytics workspace data retention in days. Possible values range between 30 and 730

Resource Graph

Authors

Originally Created by Kumaraswamy Vithanala (Kumar)

Other resources

• Hub-spoke network topology in Azure
• Terraform AzureRM Provider Documentation