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Front Door routing limits

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Important

Azure Front Door (classic) will be retired on March 31, 2027. To avoid any service disruption, it is important that you migrate your Azure Front Door (classic) profiles to Azure Front Door Standard or Premium tier by March 2027. For more information, see Azure Front Door (classic) retirement.

Each Front Door profile has a composite route limit.

Your Front Door profile's composite route metric is derived from the number of routes, and the front end domains, protocols, and paths associated with that route.

The composite route metric for each Front Door profile can't exceed 5000.

Tip

Most Front Door profiles don't approach the composite route limit. However, if you have a large Front Door profiles, consider whether you could exceed the limit and plan accordingly.

The number of origin groups, origins, and endpoints don't affect your composite routing limit. However, there are other limits that apply to these resources. For more information, see Azure subscription and service limits, quotas, and constraints.

Calculate your profile's composite limit

The composite limit of a profile is the sum of the composite routes and the composite override routes. Each route has a composite route metric, which is computed as follows:

Composite route calculation

  1. Select a route from your profile.
    1. Multiply the number of HTTP domains by the number of HTTP paths.
    2. Multiply the number of HTTPS domains by the number of HTTPS paths.
    3. Add the results of steps 1a and 1b together to give the composite route metric for this individual route.
  2. Repeat these steps for each route in your profile.

Composite route overrides calculation

The composite route overrides metric is a variation of the composite route metrics, where the number of domains is multiplied by the number of route overrides instead of the number of paths. The list of rules for each route determines the route overrides.

  1. Select a route from your profile. Let n be the number of route overrides present in the list of rules for this route.
    1. Multiply the number of HTTP domains by n.
    2. Multiply the number of HTTPS domains by n.
    3. Add the results of steps 1a and 1b together to give the composite override route metric for this individual route.
  2. Repeat these steps for each route in your profile.

Add together all of the composite route and route override metrics for each route. This number is your profile's composite limit.

Example

Suppose you have two routes in your Front Door profile. The routes are named Route 1 and Route 2. You plan to configure the routes as follows:

  • Route 1 has 50 domains associated to it, and requires HTTPS for all inbound requests. Route 1 specifies 80 paths. Route 1 also has two route overrides.
  • Route 2 has 25 domains associated to it. Route 2 specifies 25 paths, and supports both the HTTP and HTTPS protocols. Route 2 also has one route override.

The following calculation illustrates how to determine the composite route metric for this scenario:

Profile composite route metric = Route 1 composite route metric + Route 1 composite route override metric+ Route 2 composite route metric + Route 2 composite route override metric
= Route 1 [HTTPS (50 Domains * 80 Paths)] + Route 1 [Route Override (50 Domains * 2 route overrides)] + Route 2 [HTTP (25 Domains * 25 Paths) + HTTPS(25 Domains * 25 Paths)] + Route 2 [HTTP (25 Domains * 1 route override) + HTTPS(25 Domains * 1 route override)] 
= [50 * 80] + [50 * 2] + [(25 * 25) + (25 * 25)] + [(25 * 1) + (25 * 1)]
= 5400

The calculated metric of 5400 exceeds the limit of 5000, so you can't configure a Front Door profile in this way.

Mitigation

If your profile's composite route metric exceed 5000, consider the following mitigation strategies:

  • Deploy multiple Front Door profiles, and spread your routes across them. The composite route limit applies within a single profile.
  • Use wildcard domains instead of specifying subdomains individually, which might help to reduce the number of domains in your profile.
  • Require HTTPS for inbound traffic, which reduces the number of HTTP routes in your profile and also improves your solution's security.

Next steps

Learn how to create a Front Door.