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Rate Limiting - SLA-Based

The Rate Limiting policies based on a service level access (SLA) are client ID-based policies that use the client ID as a reference to impose limits on the number of requests that each application can make within a period of time. To use these policies you need to create at least one SLA tier to define request limits.

You can configure an SLA tier to require manual approval of requests from users who want to register an app to call your API.

Rate Limiting - SLA-Based Policy

SLA-based rate limiting restricts the number of requests by application to your API based on the configuration of an SLA tier. By default, you provide the Client ID and token credentials in the form of query parameters named client_id and client_secret. In Mule 4, you can choose to provide only the Client ID in your SLA policy. This is especially useful when combining this policy with a federated policy, such as OpenAM or PingFederate.

Rate limiting (not SLA-based) restricts the number of requests the API accepts from all applications within a certain time period. After reaching the limit, requests are rejected. Users don’t need to register applications or send Client IDs.

You can alter the Mule expression that points to the credentials, and obtain these values from elsewhere in the HTTP message.

SLA-Based Application Registration

If you create at least one SLA tier for an API, a user who requests access from a new application must choose an SLA tier. You can offer multiple SLA tier choices based on different rate limits and throttling.

Managing API Access Requests

If the selected SLA tier is set to automatic, then API Manager instantly approves all requests for API access, and users can immediately send authenticated requests to the API. If the selected SLA tier was configured with manual approval, an admin of your organization has to approve it before a user can start to send valid requests to your API.

To approve API access requests, go to the API version page, and select Applications.


There you can view details about your pending and processed requests and manage them.

Creating an SLA Tier or Layered SLAs

First, create an SLA tier. If you choose manual approval, any application requests for access must be manually approved by an admin in your organization.

Multiple SLA limits are supported under the following conditions:

  • API Manager manages the API

  • API Gateway runtime 2.1 or later manages the API

When an SLA tier having more than one limit is used for an API that runs on an API Gateway runtime earlier than 2.1, only the first defined limit is enforced.

You can specify multiple throughput limits for a single SLA tier.

  1. In the Add SLA Tier dialog, in Limits, set the first set of limits.

  2. Click the plus icon, and set the next set of limits.

    For example:

    # of Reqs Time Period Time Unit







  3. Click Add.

For example, an SLA tier named Gold is set to limit requests to 100 requests per second as well as a limit of 10,000 requests per day. This ensures that applications registered on the Gold tier don’t exceed a bursting limit of 100 requests per second. Traffic bottlenecks are avoided, while ensuring that registered applications get the advertised SLA of 10,000 requests per day.

If you uncheck the visible flag, the first limit of 100 requests is not exposed to application developers at registration time. When you configure only one limit, that limit must be visible.

Response Headers

Three headers are included in request responses that inform users about the SLA restrictions and inform them when nearing the threshold. When the SLA enforces multiple policies that limit request throughput, a single set of headers pertaining to the most restrictive of the policies provides this information.

For example, a user of your API may receive a response that includes these headers:

X-RateLimit-Limit: 20
X-RateLimit-Remaining: 14
X-RateLimit-Reset: 19100

Within the next 19100 milliseconds, only 14 more requests are allowed by the SLA, which is set to allow 20 within this time-window.

Rate Limiting in a Mule Cluster

The guidelines for rate limiting in a cluster applies to rate limiting for SLA-based policies.

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