Status

Current state: "Under Discussion"Accepted

Discussion thread: here

JIRA:

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

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Per-IP connection creation rate quota will be configured as a dynamic quota for entity type IPs ips.

• Default quota for <IPs> will be stored in Zookeeper at /config/IPsips/<default>
• Quota for a specific IP address for which quota override is defined will be stored in Zookeeper at /config/IPsips/<ip-address>

If per-IP or default IP quota is not configured, we will use Int.MaxValue as a default to ensure backward compatibility.

We will use the AlterClientQuota and DescribeClientQuota APIs to manage IP connection rate quotas. Adding support for IP quotas will not require any changes to the protocol, since entity type and name are represented flexibly as Strings. For ease of use, we will define a new recognized IP entity type in org.apache.kafka.common.quota.ClientQuotaEntity:

/**
 * Describes a client quota entity, which is a mapping of entity types to their names.
 */
public class ClientQuotaEntity {
 
    /**
     * The type of an entity entry.
     */
    public static final String USER = "user";
    public static final String CLIENT_ID = "client-id";
	public static final String IP = "ip";
}

Since IP quotas are orthogonal with user/client ID quotas the following is to disambiguate how the new IP entity will interact with the existing client-id and user entities.

A DescribeClientQuotasRequest constructed with a filter for both ip entities and either of user or client-id represents a logical AND of IP quotas and user/client quotas. However, since there are no quotas that satisfy both IP and either of user/client-id, such a request is likely due to user error. In such a case we will return an INVALID_REQUEST error.

Likewise, an AlterClientQuotasRequest with both an IP entity and either of user or client-id entity will return an INVALID_REQUEST error, as there are no shared quota properties between the two entity types.

Tools

kafka-configs.sh will be extended to support per-IP connection rate quotas.  A new entity type IPs will be added with the following key (and a value of type Int):

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bin/kafka-configs  --bootstrap-server localhost:9091 --alter --add-config 'connection_creation_rate=100' --entity-name 93.284.53.13 --entity-type IPsips

bin/kafka-configs  --bootstrap-server localhost:9091 --alter --add-config 'connection_creation_rate=100' --ip 93.284.53.13

Default connection rate quotas for an IP address can be configured by omitting entity name. For examplevia the following:

bin/kafka-configs  --bootstrap-server localhost:9091 --alter --add-config 'connection_creation_rate=100' --entity-type IPsips --entity-default

bin/kafka-configs  --bootstrap-server localhost:9091 --alter --add-config 'connection_creation_rate=100' --ip-defaults

Connection rate throttling behavior

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Since the broker has to accept the connection in order to know the IP address, limiting connection creation rate per IP means that the enforcement of the limit has to happen after connection is accepted. Dropping the connection right away as broker does for per-IP connection count limits (KIP-402) does not work as well for connection rate limiting, because the offending client is likely to immediately reconnect. At the same time, connection rate limiting by only delaying processing of connections would not work for cases where the connection creation rate is continuously higher than the set limits, which would create a large backlog. This case could be more common for clients that come through a proxy, and where there could be potentially a large number of incoming connections with the same IP. To address these two issues, our approach is as follows. If connection creation rate is reached for a specific IP address, the broker will delay processing the connection by an amount of time that brings the rate within the limit or 1 second, whichever is earliest. After the delay, if the per-IP quota is still violated, the connection will be cleaned up; otherwise, the connection will be accepted.

Metrics

New metrics that track broker-wide or per-listener rate of accepting connections, and are used by SocketServer to detect connection acceptance rate quota violation:

•  kafka.network:type=socket-server-metrics,name=connection-accept-rate,listener={listenerName}

  • Type: Rate
  • Description: Rate of connections accepted per second on a given listener

•  kafka.network:type=socket-server-metrics,name=broker-connection-accept-rate

  • Type: Rate
  • Description: Broker-wide rate of connections accepted per second

•  kafka.network:type=socket-server-metrics,name=connection-accept-rate,ip={ipAddress}

  • Type: Rate
  • Description: Rate of connections accepted per second for a given IP

New metrics that track average throttle time of accepting a new connection due to reaching connection acceptance rate limit:

• kafka.network:type=socket-server-metrics,name=connection-accept-throttle-time,listener={listenerName}

  • Type: SampledStat.Avg
  • Description: Average throttle time due to violating per-listener or broker-wide connection acceptance rate quota on a given listener.

• kafka.network:type=socket-server-metrics,name=ip-connection-accept-throttle-time,listener={listenerName}

  • Type: SampledStat.Avg
  • Description: Average throttle time due to violating ip connection rate quota on a given listener. IP throttling is reported at a listener granularity rather than at an IP granularity to keep a smaller metrics overhead. 

No new metrics will be added. The existing metric (kafka.network:type=Acceptor,name=AcceptorBlockedPercent,listener={listenerName}) that tracks the amount of time Acceptor is blocked from accepting connections will now additionally include the amount of time Acceptor is blocked due to hitting connection create limit (in addition to the time blocked due to hitting the maximum limit on currently active connections). 

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There will be no impact on existing users.

Rejected Alternatives

Broker configurations to set limits on per IP connection attempt rates

Add broker configurations for setting the default per-IP connection attempt limit and per-IP limit overrides:

Config option: Name: max.connection.creation.rate.per.ip Type: Int Default value: Int.MaxValue


Config option: Name: max.connection.creation.rate.per.ip.overrides Type: String Default value: ""

We chose the option of making per-IP quota similar to other quotas, configured as a dynamic quota for entity type "ip" as well as defaults. 

Use incrementalAlterConfigs/describeConfigs for IP quotas

DescribeConfigsRequest requires the user to specify a list of ConfigResource which consists of a Type and Name for which to retrieve the desired configs. An empty name indicates that we want to describe the configs for the entity type default. This works well for describing broker and topic configs, because the full list of brokers and topics is retrievable via other requests.

However, for IPs there is no mechanism for IP discovery, and DescribeConfigsRequest has no way to indicate that a request should list all configs for an entity type without also giving a list of entity names. This would make discovery of which IPs have a connection rate quota unfeasible, so this was rejectedNone.