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Enterprise Documentation

Document updated on Oct 26, 2021

Service Rate Limiting to Control API Usage

The service rate limit feature allows you to set the maximum requests per second a user or group of users can do to KrakenD and works analogously to the endpoint rate limit. There are two different strategies to set limits that you can use, simultaneously or individually:

  • Service rate-limit: Defines the rate-limit that all users of your API can do together, sharing the same counter. For instance, you might want to limit the interaction from users to KrakenD to 10,000 requests/second to avoid a possible DDoS propagating to your backend services.
  • Client rate-limit: Rate-limits what an individual user can do against all endpoints. For instance, a personal JWT token can make 100 requests/second to the API.

Both types keep in-memory an updated Token Bucket expressing the remaining requests for a user or group of users.

For additional types of rate-limiting see the Traffic management overview.

Service rate-limiting (max_rate)

The service rate limit acts on the number of simultaneous transactions KrakenD allows to process. This type of limit protects the service from all customers. In addition, these limits mitigate abusive actions such as rapidly writing content, aggressive polling, or excessive API calls.

It consumes an insignificant amount of memory as it only needs one counter for the whole system.

When the users connected to an endpoint together exceed the max_rate, KrakenD starts to reject connections with a status code 503 Service Unavailable and enables a Spike Arrest policy

Service client rate-limiting (client_max_rate)

The client or user rate limit applies to an individual user to all endpoints. Each endpoint can additionally have sub-limit rates, but all users are subject to the same rate.

The client_max_rate tracks one counter per different client.

When a single user connected to an endpoint exceeds their client_max_rate, KrakenD starts to reject connections with a status code 429 Too Many Requests and enables a Spike Arrest policy

Service rate-limiting configuration

The configuration allows you to use both types of rate limits at the same time:

{
    "version": 3,
    "extra_config": {
      "qos/ratelimit/service": {
          "max_rate": 50,
          "client_max_rate": 5,
          "strategy": "ip"
        }
    }
}
Fields of Endpoint ratelimit
* required fields

Minimum configuration needs any of: max_rate , or client_max_rate

capacity integer
Defines the maximum number of tokens a bucket can hold, or said otherwise, how many requests will you accept from all users together at any given instant. When the gateway starts, the bucket is full. As requests from users come, the remaining tokens in the bucket decrease. At the same time, the max_rate refills the bucket at the desired rate until its maximum capacity is reached. The default value for the capacity is the max_rate value expressed in seconds or 1 for smaller fractions. When unsure, use the same number as max_rate.
Defaults to 1
cleanup_period string
The cleanup period is how often the routine(s) in charge of optimizing the memory dedicated will go iterate all counters looking for outdated TTL and remove them. A low value keeps the memory slightly decreasing, but as a trade-off, it will increase the CPU dedicated to achieving this optimization. This is an advanced micro-optimization setting that should be used with caution.
Specify units using ns (nanoseconds), us or µs (microseconds), ms (milliseconds), s (seconds), m (minutes), or h (hours).
Defaults to "1m"
cleanup_threads integer
These are the number of routines that search for and remove outdated rate limit counters. The more routine(s) you add, the faster the memory optimization is completed, but the more CPU it will consume. Generally speaking, a single thread is more than enough because the delete operation is very fast, even with a large number of counters. This is an advanced micro-optimization setting that you should use with caution.
Defaults to 1
client_capacity integer
Defines the maximum number of tokens a bucket can hold, or said otherwise, how many requests will you accept from each individual user at any given instant. Works just as capacity, but instead of having one bucket for all users, keeps a counter for every connected client and endpoint, and refills from client_max_rate instead of max_rate. The client is recognized using the strategy field (an IP address, a token, a header, etc.). The default value for the client_capacity is the client_max_rate value expressed in seconds or 1 for smaller fractions. When unsure, use the same number as client_max_rate.
Defaults to 1
client_max_rate number
Number of tokens you add to the Token Bucket for each individual user (user quota) in the time interval you want (every). The remaining tokens in the bucket are the requests a specific user can do. It keeps a counter for every client and endpoint. Keep in mind that every KrakenD instance keeps its counters in memory for every single client.
every string
Time period in which the maximum rates operate. For instance, if you set an every of 10m and a rate of 5, you are allowing 5 requests every ten minutes.
Specify units using ns (nanoseconds), us or µs (microseconds), ms (milliseconds), s (seconds), m (minutes), or h (hours).
Defaults to "1s"
key string
Available when using client_max_rate and you have set a strategy equal to header or param. It makes no sense in other contexts. For header it is the header name containing the user identification (e.g., Authorization on tokens, or X-Original-Forwarded-For for IPs). When they contain a list of space-separated IPs, it will take the IP from the client that hit the first trusted proxy. For param it is the name of the placeholder used in the endpoint, like id_user for an endpoint /user/{id_user}.
Examples: "X-Tenant" , "Authorization" , "id_user"
max_rate number
Sets the maximum number of requests all users can do in the given time frame. Internally uses the Token Bucket algorithm. The absence of max_rate in the configuration or a 0 is the equivalent to no limitation. You can use decimals if needed.
num_shards integer
All rate limit counters are stored in memory in groups (shards). All counters in the same shard share a mutex (which controls that one counter is modified at a time), and this helps with contention. Having, for instance, 2048 shards (default) and 1M users connected concurrently (same instant) means that each user will need to coordinate writes in their counter with an average of under 500 other users (1M/2048=489). Lowering the shards might increase contention and latency but free additional memory. This is an advanced micro-optimization setting that should be used with caution.
Defaults to 2048
strategy
Available when using client_max_rate. Sets the strategy you will use to set client counters. Choose ip when the restrictions apply to the client’s IP address, or set it to header when there is a header that identifies a user uniquely. That header must be defined with the key entry.
Possible values are: "ip" , "header" , "param"
Schema: https://www.krakend.io/schema/v2.9/qos/ratelimit/router.json

A note on strategies:

  • "strategy": "ip" When the restrictions apply to the client’s IP, and every IP is considered to be a different user. Optionally a key can be used to extract the IP from a custom header:
    • E.g, set "key": "X-Original-Forwarded-For" to extract the IP from a header containing a list of space-separated IPs (will take the first one).
  • "strategy": "header" When the criteria for identifying a user comes from the value of a key inside the header. With this strategy, the key must also be present.
    • E.g., set "key": "X-TOKEN" to use the X-TOKEN header as the unique user identifier.

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