Azure Front Door Rules actions

An Azure Front Door Rule set consist of rules with a combination of match conditions and actions. This article provides a detailed description of actions you can use in an Azure Front Door Rule set. An action defines the behavior that gets applied to a request type that a match condition(s) identifies. In an Azure Front Door Rule set, a rule can contain up to five actions.

Azure Front Door supports server variable in a Rule set action.

The following actions are available to use in an Azure Front Door rule set:

Route configuration override

Use the route configuration override action to override the origin group or the caching configuration to use for the request. You can choose to override or honor the origin group configurations specified in the route. However, whenever you override the route configuration, you must configure caching. Otherwise, caching will be disabled for the request.

You can also override how files get cached for specific requests, including:

  • Override the caching behavior specified by the origin.
  • How query string parameters are used to generate the request's cache key.
  • The time to live (TTL) value to control how long contents stay in cache.

Properties

Property Supported values
Override origin group
  • Yes: Override the origin group used for the request.
  • No: Use the origin group specified in the route.
Caching
  • Enabled: Force caching to be enabled for the request.
  • Disabled: Force caching to be disabled for the request.

When Override origin group is set to Yes, set the following properties:

Property Supported values
Origin group The origin group that the request should be routed to. This overrides the configuration specified in the Front Door endpoint route.
Forwarding protocol The protocol for Front Door to use when forwarding the request to the origin. Supported values are HTTP only, HTTPS only, Match incoming request. This overrides the configuration specified in the Front Door endpoint route.

When Caching is set to Enabled, set the following properties:

Property Supported values
Query string caching behavior
  • Ignore Query String: Query strings aren't considered when the cache key gets generated. In ARM templates, set the queryStringCachingBehavior property to IgnoreQueryString.
  • Use query string: Each unique URL has its own cache key. In ARM templates, use the queryStringCachingBehavior of UseQueryString.
  • Ignore specified query string: Query strings specified in the parameters get excluded when the cache key gets generated. In ARM templates, set the queryStringCachingBehavior property to IgnoreSpecifiedQueryStrings.
  • Include specified query string: Query strings specified in the parameters get included when the cache key gets generated. In ARM templates, set the queryStringBehavior property to IncludeSpecifiedQueryStrings.
Query parameters The list of query string parameter names, separated by commas. This property is only set when Query string caching behavior is set to Ignore Specified Query Strings or Include Specified Query Strings.
Compression
  • Enabled: Front Door dynamically compresses content at the edge, resulting in a smaller and faster response. For more information, see File compression. In ARM templates, set the isCompressionEnabled property to Enabled.
  • Disabled. Front Door does not perform compression. In ARM templates, set the isCompressionEnabled property to Disabled.
Cache behavior
  • Honor origin: Front Door will always honor origin response header directive. If the origin directive is missing, Front Door will cache contents anywhere from 1 to 3 days. In ARM templates, set the cacheBehavior property to HonorOrigin.
  • Override always: The TTL value returned from your origin is overwritten with the value specified in the action. This behavior will only be applied if the response is cacheable. In ARM templates, set the cacheBehavior property to OverrideAlways.
  • Override if origin missing: If no TTL value gets returned from your origin, the rule sets the TTL to the value specified in the action. This behavior will only be applied if the response is cacheable. In ARM templates, set the cacheBehavior property to OverrideIfOriginMissing.
Cache duration When Cache behavior is set to Override always or Override if origin missing, these fields must specify the cache duration to use. The maximum duration is 366 days. For a value of 0 seconds, the CDN caches the content, but must revalidate each request with the origin server. This property is only set when Cache behavior is set to Override always or Override if origin missing.
  • In the Azure portal: specify the days, hours, minutes, and seconds.
  • In ARM templates: use the cacheDuration to specify the duration in the format d.hh:mm:ss.

Examples

In this example, we route all matched requests to an origin group named MyOriginGroup, regardless of the configuration in the Front Door endpoint route.

Portal screenshot showing origin group override action.

In this example, we set the cache key to include a query string parameter named customerId. Compression is enabled, and the origin's caching policies are honored.

Portal screenshot showing cache key query string action.

In this example, we override the cache expiration to 6 hours for matched requests that don't specify a cache duration already. Front Door ignores the query string when it determines the cache key, and compression is enabled.

Portal screenshot showing cache expiration action.

Modify request header

Use the modify request header action to modify the headers in the request when it is sent to your origin.

Properties

Property Supported values
Operator
  • Append: The specified header gets added to the request with the specified value. If the header is already present, the value is appended to the existing header value using string concatenation. No delimiters are added. In ARM templates, use the headerAction of Append.
  • Overwrite: The specified header gets added to the request with the specified value. If the header is already present, the specified value overwrites the existing value. In ARM templates, use the headerAction of Overwrite.
  • Delete: If the header specified in the rule is present, the header gets deleted from the request. In ARM templates, use the headerAction of Delete.
Header name The name of the header to modify.
Header value The value to append or overwrite.

Example

In this example, we append the value AdditionalValue to the MyRequestHeader request header. If the origin set the response header to a value of ValueSetByClient, then after this action is applied, the request header would have a value of ValueSetByClientAdditionalValue.

Portal screenshot showing modify request header action.

Modify response header

Use the modify response header action to modify headers that are present in responses before they are returned to your clients.

Properties

Property Supported values
Operator
  • Append: The specified header gets added to the response with the specified value. If the header is already present, the value is appended to the existing header value using string concatenation. No delimiters are added. In ARM templates, use the headerAction of Append.
  • Overwrite: The specified header gets added to the response with the specified value. If the header is already present, the specified value overwrites the existing value. In ARM templates, use the headerAction of Overwrite.
  • Delete: If the header specified in the rule is present, the header gets deleted from the response. In ARM templates, use the headerAction of Delete.
Header name The name of the header to modify.
Header value The value to append or overwrite.

Example

In this example, we delete the header with the name X-Powered-By from the responses before they are returned to the client.

Portal screenshot showing modify response header action.

URL redirect

Use the URL redirect action to redirect clients to a new URL. Clients are sent a redirection response from Front Door.

Properties

Property Supported values
Redirect type The response type to return to the requestor.
  • In the Azure portal: Found (302), Moved (301), Temporary Redirect (307), Permanent Redirect (308).
  • In ARM templates: Found, Moved, TemporaryRedirect, PermanentRedirect
Redirect protocol
  • In the Azure portal: Match Request, HTTP, HTTPS
  • In ARM templates: MatchRequest, Http, Https
Destination host The host name you want the request to be redirected to. Leave blank to preserve the incoming host.
Destination path The path to use in the redirect. Include the leading /. Leave blank to preserve the incoming path.
Query string The query string used in the redirect. Don't include the leading ?. Leave blank to preserve the incoming query string.
Destination fragment The fragment to use in the redirect. Leave blank to preserve the incoming fragment.

Example

In this example, we redirect the request to https://contoso.com/exampleredirection?clientIp={client_ip}, while preserving the fragment. An HTTP Temporary Redirect (307) is used. The IP address of the client is used in place of the {client_ip} token within the URL by using the client_ip server variable.

Portal screenshot showing URL redirect action.

URL rewrite

Use the URL rewrite action to rewrite the path of a request that's en route to your origin.

Properties

Property Supported values
Source pattern Define the source pattern in the URL path to replace. Currently, source pattern uses a prefix-based match. To match all URL paths, use a forward slash (/) as the source pattern value.
Destination Define the destination path to use in the rewrite. The destination path overwrites the source pattern.
Preserve unmatched path If set to Yes, the remaining path after the source pattern is appended to the new destination path.

Example

In this example, we rewrite all requests to the path /redirection, and don't preserve the remainder of the path.

Portal screenshot showing URL rewrite action.

In Azure Front Door (classic), a Rules engine can consist up to 25 rules containing matching conditions and associated actions. This article provides a detailed description of each action you can define in a rule.

An action defines the behavior that gets applied to the request type that matches the condition or set of match conditions. In the Rules engine configuration, a rule can have up to 10 matching conditions and 5 actions. You can only have one Override Routing Configuration action in a single rule.

The following actions are available to use in Rules engine configuration.

Modify request header

Use these actions to modify headers that are present in requests sent to your backend.

Required fields

Action HTTP header name Value
Append When this option gets selected and the rule matches, the header specified in Header name gets added to the request with the specified value. If the header is already present, the value is appended to the existing value. String
Overwrite When this option is selected and the rule matches, the header specified in Header name gets added to the request with the specified value. If the header is already present, the specified value overwrites the existing value. String
Delete When this option gets selected with matching rules and the header specified in the rule is present, the header gets deleted from the request. String

Modify response header

Use these actions to modify headers that are present in responses returned to your clients.

Required fields

Action HTTP Header name Value
Append When this option gets selected and the rule matches, the header specified in Header name gets added to the response by using the specified Value. If the header is already present, Value is appended to the existing value. String
Overwrite When this option is selected and the rule matches, the header specified in Header name is added to the response by using the specified Value. If the header is already present, Value overwrites the existing value. String
Delete When this option gets selected with matching rules and the header specified in the rule is present, the header gets deleted from the response. String

Route configuration overrides

Route Type: Redirect

Use these actions to redirect clients to a new URL.

Required fields

Field Description
Redirect type Redirect is a way to send users/clients from one URL to another. A redirect type sets the status code used by clients to understand the purpose of the redirect.

You can select the following redirect status codes: Found (302), Moved (301), Temporary redirect (307), and Permanent redirect (308).
Redirect protocol Retain the protocol as per the incoming request, or define a new protocol for the redirection. For example, select 'HTTPS' for HTTP to HTTPS redirection.
Destination host Set this to change the hostname in the URL for the redirection or otherwise retain the hostname from the incoming request.
Destination path Either retain the path as per the incoming request, or update the path in the URL for the redirection.
Query string Set this to replace any existing query string from the incoming request URL or otherwise retain the original set of query strings.
Destination fragment The destination fragment is the portion of URL after '#', normally used by browsers to land on a specific section on a page. Set this to add a fragment to the redirect URL.

Route Type: Forward

Use these actions to forward clients to a new URL. These actions also contain sub actions for URL rewrites and caching.

Field Description
Backend pool Select the backend pool to override and serve the requests, this will also show all your pre-configured backend pools currently in your Front Door profile.
Forwarding protocol Protocol to use for forwarding request to backend or match the protocol from incoming request.
URL rewrite Path to use when constructing the request for URL rewrite to forward to the backend.
Caching Enable caching for this routing rule. When enabled, Azure Front Door will cache your static content.

URL rewrite

Use this setting to configure an optional Custom Forwarding Path to use when constructing the request to forward to the backend.

Field Description
Custom forwarding path Define a path for which requests will be forwarded to.

Caching

Use these settings to control how files get cached for requests that contain query strings. Whether to cache your content based on all parameters or on selected parameters. You can use additional settings to overwrite the time to live (TTL) value to control how long contents stay in cache. To force caching as an action, set the caching field to "Enabled." When you force caching, the following options appear:

Cache behavior Description
Ignore query strings Once the asset is cached, all ensuing requests ignore the query strings until the cached asset expires.
Cache every unique URL Each request with a unique URL, including the query string, is treated as a unique asset with its own cache.
Ignore specified query strings Request URL query strings listed in "Query parameters" setting are ignored for caching.
Include specified query strings Request URL query strings listed in "Query parameters" setting are used for caching.
Additional fields Description
Dynamic compression Front Door can dynamically compress content on the edge, resulting in a smaller and faster response.
Query parameters A comma-separated list of allowed or disallowed parameters to use as a basis for caching.
Use default cache duration Set to use Azure Front Door default caching duration or define a caching duration which ignores the origin response directive.

Next steps