Throttling Tiers

In WSO2 API Manager, an API, application or a resource can be available to a consumer at different levels of service. This is facilitated by throttling tiers. Throttling tiers are used to limit the number of hits to an API during a given period of time, typically in cases of infrastructure limitations, security concerns (preventing DOS attacks), monetization purposes etc.

For example, if you have infrastructure limitations in facilitating more than a certain number of requests to an API at a time, set throttling tiers to the APIs to limit access to it accordingly. Each tier defines a maximum number of requests per minute. The API Manager comes with three default tiers as Gold, Silver and Bronze.   

• Bronze - Allows 1 request for the API per minute
• Silver - Allows 5 requests for the API per minute
• Gold - Allows 20 requests for the API per minute

In addition, there is also a special tier called Unlimited, which allows unlimited access. It can be disabled by editing the <TierManagement> node of the api-manager.xml file. You can also add your own tiers to the API Manager using the instructions in section Adding New Throttling Tiers.

Throttling is enabled in API Manager in 3 different levels. The topics below describe this:

API-level throttling

API-level throttling tiers are defined when Creating an API using the API Publisher. At subscription time, the consumers of the API can log in to the API Store and select which tier they are interested in as follows:

According to the tiers s/he selects, the subscriber is granted a maximum number of requests to the API.

Setting tier permissions

Users with Manage Tiers permission can set role-based permissions to API-level access throttling tiers. This is done using the Tier Permissions menu of API Publisher as shown below. For each tier, you can specify a comma-separated list of roles and either Allow or Deny access to the list.

A subscriber logged into the API Store can consume APIs using a specific tier, only if s/he is assigned to a role that is allowed access. In the API Store, the subscriber sees a list of tiers that is filtered based on the subscriber's role. Only the ALLOWED roles appear here. By default, all tiers are allowed to everyone.

Application-level throttling

Application-level throttling tiers are defined at the time an application is created using the API Store. For information, see  Applications and application-level throttling.

Resource-level throttling

How throttling tiers work

• When an API is invoked, it first checks whether the request is allowed by application-level throttling limit. If an application has exceeded its maximum number of allowed requests, the new request will be terminated.
• If application-level limit is not exceeded, it then checks whether the request is allowed by resource-level throttling limit. If it has exceeded, the request will be terminated.
• If resource-level limit is not exceeded, it finally checks whether the request is allowed by API-level throttling limit. If the limit is not exceeded, then the request will be granted.

With capability to define throttling at three levels, the final request limit granted to a given user on a given API is ultimately defined by the consolidated output of all throttling tiers together. For example, lets say two users subscribe to an API using the Gold subscription, which allows 20 requests per minute. They both use the application App1 for this subscription, which again has a throttling tier set to 20 requests per minute. All resource level throttling tiers are unlimited. In this scenario, although both users are eligible for 20 requests per minute access to the API, each ideally has a limit of only 10 requests per minute. This is due to the application-level limitation of 20 requests per minute.

Go back to Tier Availability section in Creating an API page.