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.
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
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.
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.