Networking overview for Azure Database for PostgreSQL - Flexible Server with private access (VNET Integration)

APPLIES TO: Azure Database for PostgreSQL - Flexible Server

This article describes connectivity and networking concepts for Azure Database for PostgreSQL flexible server.

When you create an Azure Database for PostgreSQL flexible server instance, you must choose one of the following networking options: Private access (VNet integration) or Public access (allowed IP addresses) and Private Endpoint. This document will describe Private access (VNet integration) networking option.

Private access (VNet integration)

You can deploy an Azure Database for PostgreSQL flexible server instance into your Azure virtual network (VNet) using VNET injection. Azure virtual networks provide private and secure network communication. Resources in a virtual network can communicate through private IP addresses that were assigned on this network.

Choose this networking option if you want the following capabilities:

• Connect from Azure resources in the same virtual network to your Azure Database for PostgreSQL flexible server instance by using private IP addresses.
• Use VPN or Azure ExpressRoute to connect from non-Azure resources to your Azure Database for PostgreSQL flexible server instance.
• Ensure that the Azure Database for PostgreSQL flexible server instance has no public endpoint that's accessible through the internet.

In the preceding diagram:

• Azure Databases for PostgreSQL flexible server instances are injected into subnet 10.0.1.0/24 of the VNet-1 virtual network.
• Applications that are deployed on different subnets within the same virtual network can access Azure Database for PostgreSQL flexible server instances directly.
• Applications that are deployed on a different virtual network (VNet-2) don't have direct access to Azure Database for PostgreSQL flexible server instances. You have to perform virtual network peering for a private DNS zone before they can access the flexible server.

Virtual network concepts

An Azure virtual network contains a private IP address space that's configured for your use. Your virtual network must be in the same Azure region as your Azure Database for PostgreSQL flexible server instance. To learn more about virtual networks, see the Azure Virtual Network overview.

Here are some concepts to be familiar with when you're using virtual networks where resources are integrated into virtual network with Azure Database for PostgreSQL flexible server instances:

• Delegated subnet. A virtual network contains subnets (subnetworks). Subnets enable you to segment your virtual network into smaller address spaces. Azure resources are deployed into specific subnets within a virtual network.

  Your VNET integrated Azure Database for PostgreSQL flexible server instance must be in a subnet that's delegated. That is, only Azure Database for PostgreSQL flexible server instances can use that subnet. No other Azure resource types can be in the delegated subnet. You delegate a subnet by assigning its delegation property as Microsoft.DBforPostgreSQL/flexibleServers. The smallest CIDR range you can specify for the subnet is /28, which provides 16 IP addresses, however the first and last address in any network or subnet can't be assigned to any individual host. Azure reserves five IPs to be utilized internally by Azure networking, which include two IPs that can't be assigned to host, mentioned above. This leaves you 11 available IP addresses for /28 CIDR range, whereas a single Azure Database for PostgreSQL flexible server instance with High Availability features utilizes four addresses. For Replication and Microsoft Entra connections, please make sure Route Tables don't affect traffic.A common pattern is routed all outbound traffic via an Azure Firewall or a custom on-premises network filtering appliance. If the subnet has a Route Table associated with the rule to route all traffic to a virtual appliance:

  • Add a rule with Destination Service Tag “AzureActiveDirectory” and next hop “Internet”
  • Add a rule with Destination IP range same as the Azure Database for PostgreSQL flexible server subnet range and next hop “Virtual Network”

  Important

  The names AzureFirewallSubnet, AzureFirewallManagementSubnet, AzureBastionSubnet, and GatewaySubnet are reserved within Azure. Don't use any of these as your subnet name.

• Network security group (NSG). Security rules in NSGs enable you to filter the type of network traffic that can flow in and out of virtual network subnets and network interfaces. For more information, see the NSG overview.

  Application security groups (ASGs) make it easy to control Layer-4 security by using NSGs for flat networks. You can quickly:

  • Join virtual machines to an ASG, or remove virtual machines from an ASG.
  • Dynamically apply rules to those virtual machines, or remove rules from those virtual machines.

  For more information, see the ASG overview.

  At this time, we don't support NSGs where an ASG is part of the rule with Azure Database for PostgreSQL flexible server. We currently advise using IP-based source or destination filtering in an NSG.

  Important

  High availability and other Features of Azure Database for PostgreSQL flexible server require ability to send/receive traffic to destination port 5432 within Azure virtual network subnet where Azure Database for PostgreSQL flexible server is deployed, as well as to Azure storage for log archival. If you create Network Security Groups (NSG) to deny traffic flow to or from your Azure Database for PostgreSQL flexible server instance within the subnet where it's deployed, make sure to allow traffic to destination port 5432 within the subnet, and also to Azure storage by using service tag Azure Storage as a destination. You can further filter this exception rule by adding your Azure region to the label like us-east.storage. Also, if you elect to use Microsoft Entra authentication to authenticate logins to your Azure Database for PostgreSQL flexible server instance, allow outbound traffic to Microsoft Entra ID using Microsoft Entra service tag. When setting up Read Replicas across Azure regions, Azure Database for PostgreSQL flexible server requires ability to send/receive traffic to destination port 5432 for both primary and replica, as well as to Azure storage in primary and replica regions from both primary and replica servers.

• Private DNS zone integration. Azure private DNS zone integration allows you to resolve the private DNS within the current virtual network or any in-region peered virtual network where the private DNS zone is linked.

Using a private DNS zone

Azure Private DNS provides a reliable and secure DNS service for your virtual network. Azure Private DNS manages and resolves domain names in the virtual network without the need to configure a custom DNS solution.

When using private network access with Azure virtual network, providing the private DNS zone information is mandatory in order to be able to do DNS resolution. For new Azure Database for PostgreSQL flexible server instance creation using private network access, private DNS zones need to be used while configuring Azure Database for PostgreSQL flexible server instances with private access. For new Azure Database for PostgreSQL flexible server instance creation using private network access with API, ARM, or Terraform, create private DNS zones and use them while configuring Azure Database for PostgreSQL flexible server instances with private access. See more information on REST API specifications for Microsoft Azure. If you use the Azure portal or Azure CLI for creating Azure Database for PostgreSQL flexible server instances, you can either provide a private DNS zone name that you had previously created in the same or a different subscription or a default private DNS zone is automatically created in your subscription.

If you use an Azure API, an Azure Resource Manager template (ARM template), or Terraform, create private DNS zones that end with .postgres.database.azure.com. Use those zones while configuring Azure Database for PostgreSQL flexible server instances with private access. For example, use the form [name1].[name2].postgres.database.azure.com or [name].postgres.database.azure.com. If you choose to use the form [name].postgres.database.azure.com, the name can't be the name you use for one of your Azure Databases for PostgreSQL flexible server instances or an error message will be shown during provisioning. For more information, see the private DNS zones overview.

Using Azure portal, API, CLI or ARM, you can also change private DNS Zone from the one you provided when creating your Azure Database for PostgreSQL flexible server instance to another private DNS zone that exists the same or different subscription.

After you create a private DNS zone in Azure, you need to link a virtual network to it. Once linked, resources hosted in that virtual network can access the private DNS zone.

DNS private zones are resilient to regional outages because zone data is globally available. Resource records in a private zone are automatically replicated across regions. Azure Private DNS is an availability zone foundational, zone-reduntant service. For more information, see Azure services with availability zone support.

Integration with a custom DNS server

If you're using a custom DNS server, you must use a DNS forwarder to resolve the FQDN of Azure Database for PostgreSQL flexible server. The forwarder IP address should be 168.63.129.16.

The custom DNS server should be inside the virtual network or reachable via the virtual network's DNS server setting. To learn more, see Name resolution that uses your own DNS server.

Private DNS zone and virtual network peering

Private DNS zone settings and virtual network peering are independent of each other. If you want to connect to the Azure Database for PostgreSQL flexible server instance from a client that's provisioned in another virtual network from the same region or a different region, you have to link the private DNS zone with the virtual network. For more information, see Link the virtual network.

To map a Server name to the DNS record, you can run nslookup command in Azure Cloud Shell using Azure PowerShell or Bash, substituting name of your server for <server_name> parameter in example below:

nslookup -debug <server_name>.postgres.database.azure.com | grep 'canonical name'

Using Hub and Spoke private networking design

Hub and spoke is a popular networking model for efficiently managing common communication or security requirements.

The hub is a virtual network that acts as a central location for managing external connectivity. It also hosts services used by multiple workloads. The hub coordinates all communications to and from the spokes. IT rules or processes like security can inspect, route, and centrally manage traffic. The spokes are virtual networks that host workloads, and connect to the central hub through virtual network peering. Shared services are hosted in their own subnets for sharing with the spokes. A perimeter subnet then acts as a security appliance.

The spokes are also virtual networks in Azure, used to isolate individual workloads. The traffic flow between the on-premises headquarters and Azure is connected through ExpressRoute or Site to Site VPN, connected to the hub virtual network. The virtual networks from the spokes to the hub are peered, and enable communication to on-premises resources. You can implement the hub and each spoke in separate subscriptions or resource groups.

There are three main patterns for connecting spoke virtual networks to each other:

• Spokes directly connected to each other. Virtual network peerings or VPN tunnels are created between the spoke virtual networks to provide direct connectivity without traversing the hub virtual network.
• Spokes communicate over a network appliance. Each spoke virtual network has a peering to Virtual WAN or to a hub virtual network. An appliance routes traffic from spoke to spoke. The appliance can be managed by Microsoft (as with Virtual WAN) or by you.
• Virtual Network Gateway attached to the hub network and make use of User Defined Routes (UDR), to enable communication between the spokes.

Use Azure Virtual Network Manager (AVNM) to create new (and onboard existing) hub and spoke virtual network topologies for the central management of connectivity and security controls.

Communication with privately networked clients in different regions

Frequently customers have a need to connect to clients different Azure regions. More specifically, this question typically boils down to how to connect two VNETs (one of which has Azure Database for PostgreSQL - Flexible Server and another application client) that are in different regions. There are multiple ways to achieve such connectivity, some of which are:

• Global VNET peering. Most common methodology, as it's the easiest way to connect networks in different regions together. Global VNET peering creates a connection over the Azure backbone directly between the two peered VNETs. This provides best network throughput and lowest latencies for connectivity using this method. When VNETs are peered, Azure will also handle the routing automatically for you, these VNETs can communicate with all resources in the peered VNET, established on a VPN gateway.
• VNET-to-VNET connection. A VNET-to-VNET connection is essentially a VPN between the two different Azure locations. The VNET-to-VNET connection is established on a VPN gateway. This means your traffic incurs two additional traffic hops as compared to global VNET peering. There's also additional latency and lower bandwidth as compared to that method.
• Communication via network appliance in Hub and Spoke architecture. Instead of connecting spoke virtual networks directly to each other, you can use network appliances to forward traffic between spokes. Network appliances provide more network services like deep packet inspection and traffic segmentation or monitoring, but they can introduce latency and performance bottlenecks if they're not properly sized.

Replication across Azure regions and virtual networks with private networking

Database replication is the process of copying data from a central or primary server to multiple servers known as replicas. The primary server accepts read and write operations whereas the replicas serve read-only transactions. The primary server and replicas collectively form a database cluster. The goal of database replication is to ensure redundancy, consistency, high availability, and accessibility of data, especially in high-traffic, mission-critical applications.

Azure Database for PostgreSQL flexible server offers two methods for replications: physical (i.e. streaming) via built -in Read Replica feature and logical replication. Both are ideal for different use cases, and a user may choose one over the other depending on the end goal.

Replication across Azure regions, with separate virtual networks (VNETs) in each region, requires connectivity across regional virtual network boundaries that can be provided via virtual network peering or in Hub and Spoke architectures via network appliance.

By default DNS name resolution is scoped to a virtual network. This means that any client in one virtual network (VNET1) is unable to resolve the Azure Database for PostgreSQL flexible server FQDN in another virtual network (VNET2).

In order to resolve this issue, you must make sure clients in VNET1 can access the Azure Database for PostgreSQL flexible server Private DNS Zone. This can be achieved by adding a virtual network link to the Private DNS Zone of your Azure Database for PostgreSQL flexible server instance.

Unsupported virtual network scenarios

Here are some limitations for working with virtual networks created via VNET integration:

• After an Azure Database for PostgreSQL flexible server instance is deployed to a virtual network and subnet, you can't move it to another virtual network or subnet. You can't move the virtual network into another resource group or subscription.
• Subnet size (address spaces) can't be increased after resources exist in the subnet.
• VNET injected resources can't interact with Private Link by default. If you want to use Private Link for private networking, see Azure Database for PostgreSQL flexible server networking with Private Link

Host name

Regardless of the networking option that you choose, we recommend that you always use an FQDN as host name when connecting to your Azure Database for PostgreSQL flexible server instance. The server's IP address isn't guaranteed to remain static. Using the FQDN helps you avoid making changes to your connection string.

An example that uses an FQDN as a host name is hostname = servername.postgres.database.azure.com. Where possible, avoid using hostname = 10.0.0.4 (a private address) or hostname = 40.2.45.67 (a public address).

Next steps

• Learn how to create an Azure Database for PostgreSQL flexible server instance by using the Private access (VNet integration) option in the Azure portal or the Azure CLI.