Azure Frontdoor Rule to Match ISO-639 Locale using Regex

Azure Frontdoor is a powerful tool for delivering fast, reliable, and secure access to your web applications. It allows you to define rules that determine how incoming requests should be handled, based on various factors such as the client's location, the requested URL, and the HTTP headers. One of the things you can do with Azure Frontdoor is to match the client's locale, which is a setting that indicates the language and regional preferences of the user. This can be useful for delivering localized content to your users, or for implementing language-based routing.

In this article, we will show you how to create a rule in Azure Frontdoor that matches the client's locale using regular expressions (regex). This will allow you to specify more complex patterns than the built-in locale matching options, and to handle a wider range of locales. We will assume that you have some basic knowledge of Azure Frontdoor and regular expressions, but we will try to explain everything in a way that is easy to understand for entry-level users.

Prerequisites

Before you can create a rule that matches the client's locale using regex, you need to have an Azure Frontdoor profile and a frontend host. A frontend host is a DNS name that you use to access your web application through Azure Frontdoor. You can create a frontend host when you create a new Azure Frontdoor profile, or you can add it later.

To create a new Azure Frontdoor profile, you can follow the instructions in the Azure Frontdoor quickstart. This will guide you through the process of creating a new profile, adding a frontend host, and configuring the basic settings. Once you have created your profile and frontend host, you can move on to the next step.

Creating a rule that matches the client's locale using regex

To create a rule that matches the client's locale using regex, you need to follow these steps:

1. Go to the Azure Portal and select your Azure Frontdoor profile.
2. In the left-hand menu, select Rules and then Add a rule.
3. In the Name field, enter a name for your rule. This can be any name that you like, and it is only used to identify the rule in the Azure Portal.
4. In the Match type field, select Request headers.
5. In the Header name field, enter Accept-Language. This is the HTTP header that contains the client's locale information.
6. In the Operator field, select Matches regex.
7. In the Value field, enter the regular expression that you want to use to match the client's locale. This can be any valid regular expression, but it should match the format of the Accept-Language header, which is a comma-separated list of locale codes. For example, if you want to match the English (US) locale, you can use the regular expression en-US.
8. In the Action field, select the action that you want to take when the rule matches. This can be any valid action, such as Forward or Redirect.
9. Click Add to save your rule.

Once you have created your rule, it will be applied to all incoming requests that match the regular expression you specified. You can create multiple rules to handle different locales, or to perform different actions based on the locale. For example, you could create a rule that matches the English (US) locale and forwards the request to one server, and a rule that matches the Spanish (Spain) locale and forwards the request to another server. This would allow you to deliver localized content to your users, and to route them to the appropriate server based on their language preferences.

Examples

Here are some examples of regular expressions that you can use to match the client's locale in Azure Frontdoor:

• en-US: Matches the English (US) locale.
• en-*: Matches any English locale, such as en-US, en-GB, or en-CA.
• [a-z]{2}-[A-Z]{2}: Matches any two-letter language code followed by a two-letter country code, such as en-US, fr-FR, or de-DE.
• ^[a-z]{2}-[A-Z]{2}$: Matches only two-letter language codes followed by two-letter country codes, and nothing else. This will exclude any other headers or values that might be present in the Accept-Language header.

In this article, we have shown you how to create a rule in Azure Frontdoor that matches the client's locale using regular expressions. This allows you to specify more complex patterns than the built-in locale matching options, and to handle a wider range of locales. We hope that this article has been helpful, and that you can now use this feature to deliver localized content to your users, and to route them to the appropriate server based on their language preferences.

References