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Inbound and outbound IP addresses in Azure App Service

  • บทความ

Azure App Service is a multitenant service, except for App Service Environments. Apps that aren't in an App Service environment (not in the Isolated tier) share network infrastructure with other apps. As a result, the inbound and outbound IP addresses of an app can be different, and can even change in certain situations.

App Service Environments use dedicated network infrastructures, so apps running in an App Service environment get static, dedicated IP addresses both for inbound and outbound connections.

How IP addresses work in App Service

An App Service app runs in an App Service plan, and App Service plans are deployed into one of the deployment units in the Azure infrastructure (internally called a webspace). Each deployment unit is assigned a set of virtual IP addresses, which includes one public inbound IP address and a set of outbound IP addresses. All App Service plans in the same deployment unit, and app instances that run in them, share the same set of virtual IP addresses. For an App Service Environment (an App Service plan in Isolated tier), the App Service plan is the deployment unit itself, so the virtual IP addresses are dedicated to it as a result.

Because you're not allowed to move an App Service plan between deployment units, the virtual IP addresses assigned to your app usually remain the same, but there are exceptions.

When inbound IP changes

Regardless of the number of scaled-out instances, each app has a single inbound IP address. The inbound IP address may change when you perform one of the following actions:

  • Delete an app and recreate it in a different resource group (deployment unit may change).
  • Delete the last app in a resource group and region combination and recreate it (deployment unit may change).
  • Delete an existing IP-based TLS/SSL binding, such as during certificate renewal (see Renew certificate).

Find the inbound IP

Just run the following command in a local terminal:

nslookup <app-name>.azurewebsites.net

Get a static inbound IP

Sometimes you might want a dedicated, static IP address for your app. To get a static inbound IP address, you need to secure a custom DNS name with an IP-based certificate binding. If you don't actually need TLS functionality to secure your app, you can even upload a self-signed certificate for this binding. In an IP-based TLS binding, the certificate is bound to the IP address itself, so App Service creates a static IP address to make it happen.

When outbound IPs change

Regardless of the number of scaled-out instances, each app has a set number of outbound IP addresses at any given time. Any outbound connection from the App Service app, such as to a back-end database, uses one of the outbound IP addresses as the origin IP address. The IP address to use is selected randomly at runtime, so your back-end service must open its firewall to all the outbound IP addresses for your app.

The set of outbound IP addresses for your app changes when you perform one of the following actions:

  • Delete an app and recreate it in a different resource group (deployment unit may change).
  • Delete the last app in a resource group and region combination and recreate it (deployment unit may change).
  • Scale your app between the lower tiers (Basic, Standard, and Premium), the PremiumV2 tier, the PremiumV3 tier, and the Pmv3 options within the PremiumV3 tier (IP addresses may be added to or subtracted from the set).

You can find the set of all possible outbound IP addresses your app can use, regardless of pricing tiers, by looking for the possibleOutboundIpAddresses property or in the Additional Outbound IP Addresses field in the Properties page in the Azure portal. See Find outbound IPs.

The set of all possible outbound IP addresses can increase over time if App Service adds new pricing tiers or options to existing App Service deployments. For example, if App Service adds the PremiumV3 tier to an existing App Service deployment, then the set of all possible outbound IP addresses increases. Similarly, if App Service adds new Pmv3 options to a deployment that already supports the PremiumV3 tier, then the set of all possible outbound IP addresses increases. Adding IP addresses to a deployment has no immediate effect since the outbound IP addresses for running applications don't change when a new pricing tier or option is added to an App Service deployment. However, if applications switch to a new pricing tier or option that wasn't previously available, then new outbound addresses are used and customers need to update downstream firewall rules and IP address restrictions.

Find outbound IPs

To find the outbound IP addresses currently used by your app in the Azure portal, select Properties in your app's left-hand navigation. They're listed in the Outbound IP Addresses field.

You can find the same information by running the following command in the Cloud Shell.

az webapp show --resource-group <group_name> --name <app_name> --query outboundIpAddresses --output tsv

(Get-AzWebApp -ResourceGroup <group_name> -name <app_name>).OutboundIpAddresses

To find all possible outbound IP addresses for your app, regardless of pricing tiers, select Properties in your app's left-hand navigation. They're listed in the Additional Outbound IP Addresses field.

You can find the same information by running the following command in the Cloud Shell.

az webapp show --resource-group <group_name> --name <app_name> --query possibleOutboundIpAddresses --output tsv

(Get-AzWebApp -ResourceGroup <group_name> -name <app_name>).PossibleOutboundIpAddresses

For function apps, see Function app outbound IP addresses.

Get a static outbound IP

You can control the IP address of outbound traffic from your app by using virtual network integration together with a virtual network NAT gateway to direct traffic through a static public IP address. Virtual network integration is available on Basic, Standard, Premium, PremiumV2, and PremiumV3 App Service plans. To learn more about this setup, see NAT gateway integration.

Service tag

By using the AppService service tag, you can define network access for the Azure App Service service without specifying individual IP addresses. The service tag is a group of IP address prefixes that you use to minimize the complexity of creating security rules. When you use service tags, Azure automatically updates the IP addresses as they change for the service. However, the service tag isn't a security control mechanism. The service tag is merely a list of IP addresses.

The AppService service tag includes only the inbound IP addresses of multitenant apps. Inbound IP addresses from apps deployed in isolated (App Service Environment) and apps using IP-based TLS bindings aren't included. Further all outbound IP addresses used in both multitenant and isolated aren't included in the tag.

The tag can be used to allow outbound traffic in a Network security group (NSG) to apps. If the app is using IP-based TLS or the app is deployed in isolated mode, you must use the dedicated IP address instead.

Note

Service tag helps you define network access, but it shouldn't be considered as a replacement for proper network security measures as it doesn't provide granular control over individual IP addresses.

Next steps