Status

Current state: Under Discussion

Discussion thread: here

JIRA: KAFKA-3492

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Motivation

KIP-13 introduced client quotas in Kafka 0.9.0.0. Rate limits on producers and consumers are enforced to prevent clients saturating the network or monopolizing broker resources. The current implementation allocates quotas to client-ids. This works well in single user clusters or clusters that use PLAINTEXT where all users have the same identity. But since client-id is unauthenticated and can be set to any value by the client, multi-tenant secure installations require quotas to be enforced for authenticated principals to guarantee fair allocation of resources and prevent denial-of-service.

This KIP addresses the following extensions to the existing implementation:

1. The option to apply quotas based on authenticated principal instead of client-id. This prevents users generating heavy traffic from monopolizing resources and impacting the performance of other users in a multi-tenant cluster.
2. Sub-quotas for clients of an authenticated user.  Like the current client-id implementation, this enables a user to rate-limit some producers or consumers to ensure that they don’t impact other more critical clients.  For instance, users may be able to rate-limit an auditing client running in the background, leaving resources always available for a critical event processing client.

Public Interfaces

Configuration Options

A configuration option quota.secure will be added to choose between the existing client-id based implementation and the new authenticated-principal based implementation.  The default value will be false to be consistent with Kafka 0.9.0.x.

Default quota configs will apply to authenticated user principals if quota.secure=true.

• quota.producer.default: If quota.secure=false, this is the default producer quota for each unique client- id. Otherwise, this is the default quota for each authenticated principal.
• quota.consumer.default: If quota.secure=false, this is the default consumer quota for each client-id. Otherwise, this is the default quota for each authenticated principal.

Metrics

When quota.secure=true, quota related metrics will be generated for authenticated principals rather than client-ids.

Tools

kafka-configs.sh will be extended to support authenticated user quotas and sub-quotas for clients of a user.  A new entity type “users” will be added.  The key-value pairs supported for users will be:

• producer_byte_rate=p : The total rate limit for the user’s producers is set to p bytes/sec
• consumer_byte_rate=c : The total rate limit for the user’s consumers is set to c bytes/sec
• client_producer_byte_rates=clientA=pA,clientB=pB : The rate limit for the user’s producers with client-id clientA is set to pA bytes/sec. Similarly for clientB. Other clients of the user share p-pA-pB bytes/sec.
• client_consumer_byte_rates=clientA=cA,clientB=cB : The rate limit for the user’s consumers with client-id clientA is set to cA bytes/sec. Other clients of the user share c-cA-cB bytes/sec.

Proposed Changes

Authenticated Principal 

Authenticated user principal will be obtained from the Session when quota.secure=true. Base64-encoded hex string version of the Principal will be used so that it can be used as a node name in Zookeeper and as the metric name without placing any restrictions on the characters allowed in the principal. 
 

Quota Configuration

Quotas are currently configured as the total rate limits (p, c) for all the producer or consumers with a specific client-id. Default values are specified in server.properties (quota.producer.default=defaultP, quota.consumer.default=defaultC) for client-ids which don’t have a config override. Producer quotas and consumer quotas can be configured independently and default values are applied when an override is not specified. In the examples below, both are overridden together for simplicity.

1. Current Implementation: Client-id based quota (quota.secure=false): { clientA : (pA, cA) }
   • pA (or cA) is the total producer (or consumer) rate limit for all clients with client-id clientA
   • Clients with a different client-id clientX with no overrides use the default rate limit of (defaultP, defaultC).
2. Authenticated-principal based quota (quota.secure=true): { user1 : (p1,c1) }
   • p1 (or c1) is the total producer (or consumer) rate limit for all clients with the authenticated principal user1
   • The total rate limit for all clients with another authenticated principal user10 with no overrides is the default rate limit of (defaultP, defaultC).
3. Hierarchical quotas for clients of a user (quota.secure=true):{ user2 : { total : (p2, c2), clientA : (p2A, c2A), clientB : (p2B, c2B)}}
   • p2A (or c2A) is the producer (or consumer) rate limit for the clients with client-id clientA AND user principal user2
   • (p2 –p2A –p2B) is the total producer rate limit for clients with any client-id other than clientA/clientB with the user principal user2. Only the total quota for these clients is enforced, per-client quota is enforced only for clientA and clientB. Similarly for consumer quotas.
   • All clients with another authenticated principal user10 will share the default rate limit of (defaultP, defaultC).
   • The basic authenticated-principal based quota (2) is simply a special case of hierarchical quotas when no client-specific quotas are specified for a user.

// Quotas for user1 (without sub-quotas)
{
    "version":1,
    "config": {
        "producer_byte_rate" : "1024",
        "consumer_byte_rate" : "2048"
    }
}
// Quotas for user2 (with sub-quotas)
{
    "version":1,
    "config": {
        "producer_byte_rate" : "1024",
        "consumer_byte_rate" : "2048",
        "client_producer_byte_rates" : "clientA=10,clientB=30",
        "client_consumer_byte_rates" : "clientA=20,clientB=40"
    }
} 

Quota Identifier

Quota configuration and metrics currently use client-id as the unique key, enforcing one quota for all clients with the same client-id. This will be replaced with a new quota-id. Each quota-id is associated with a pair of producer and consumer rate limits which may be config overrides or the default quota.  

quota.secure=false

• Client-id is used as quota-id (Current implementation)
• Each client–id with a quota override uses the overridden limits
• Each client-id without an override gets the default limits (defaultP, defaultC)

quota.secure=true

• Authenticated principal is used as quota-id if a sub-quota is not specified for the client-id. Otherwise quota-id is the concatenation of principal and client-id. Note that user principals will be base64 encoded hex in the actual implementation, but are shown here as names for readability.

• Example: {user1 : { total: (p1,c1) },  user2 : { total : (p2, c2), clientA : (p2A, c2A), clientB : (p2B, c2B) }}

  • All clients of user1 use the quota-id user1. This shares (p1, c1) amongst the clients of user1 with no individual limits for client-ids.
  • clientA of user2 uses the quota-id user2clientA. This gives clients of user2 with client-id clientA a quota of (p2A, c2A). Similarly for clients with client-id clientB.

  • clientX of user2 uses the quota-id user2. clientY of user2 also uses the same quota-id user2. Hence clientX and clientY share (p2-p2A-p2B, c2-c2A-c2B)
  • All clients of a different user10 use the quota-id user10. This shares (defaultP, defaultC) amongst the clients of user10.

Quota Persistence in Zookeeper

Client-id based quotas will continue be stored under /config/clients. Authenticated user quotas will be stored under /config/users. Only one of these will be processed and watched by the brokers depending on the value of quota.secure. Note that Base64-encoded hex version of the user principal will be used as node name under /config/users to cope with Zookeeper naming restrictions.

Tools

kafka-configs.sh will be extended to support a new entity type "users". Quota configuration for users will be provided as key-value pairs to be consistent with other configuration options. Hence no new command line arguments will be added to the tool. The tool will parse the key-value pairs specifying total user quota and possibly some client quotas, validate these and convert them to the equivalent JSON for persistence in Zookeeper.

Compatibility, Deprecation, and Migration Plan

quota.secure is set to  false as default to be consistent with Kafka 0.9.0.x. Hence the existing quota configurations will apply if new secure quotas are not defined. If quota.secure  is set to true and default or new quotas are configured for users, clients may be throttled based on the quota limits. But no client API changes are necessary to work with the new implementation.

Rejected Alternatives

Unified configuration for client-id and authenticated-principal based quotas

This KIP proposes to use a broker configuration option to switch between client-id based quotas and authenticated-principal based quotas for simplicity. An alternative would be to define a unified configuration where client-id based quotas are a special case of a unified quota config with the same username applied to all clients. The internal quota implementation will use common code for both options with only the quota-id being different. But the externally visible configuration and defaults are much simpler to define with separate options that are consistent with 0.9.0.x since it is unlikely that a cluster would support both.