Note that this KIP proposal is derived from a proposal by Grant Henke that was part of KIP-4 - Command line and centralized administrative operations.

Status

Current state: Draft

Discussion thread: TBD

JIRA:  KAFKA-3267 - Getting issue details... STATUS

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

Motivation

KIP-4 - Command line and centralized administrative operations outlines the motivation for exposing admin operations via the protocol:

• Allows clients in any language to administrate Kafka
  • Wire protocol is supported by any language
• Provides public client for performing admin operations
  • Ensures integration test code in other projects and clients maintains compatibility
  • Prevents users from needing to use the Command classes and work around standard output and system exits
• Removing the need for admin scripts (kafka-configs.sh, kafka-topics.sh, etc) to talk directly to Zookeeper. 
  • Allows ZNodes to be completely locked down via ACLs
  • Further hides the Zookeeper details of Kafka

A couple of specific use cases are worth pointing out:

1. The Metadata request exposes topic metadata, but it does not expose topic configs. ListConfigs will make that information available to any client of the Kafka protocol (including the upcoming Java AdminClient).
2. AlterConfigs would make it possible to update topic configs, but also client and replication quotas via the protocol.

Public Interfaces

List Configs

ListConfigs Request (Version: 0) => [entities]   
  entities => entity_type entity_name
    entity_type => INT8
    entity_name => STRING

Request semantics:

1. Can be sent to any broker
2. If there are multiple instructions for the same entity in one request the extra request will be ignored
   • This is because the list of entities is modeled server side as a set
   • Multiple entities results in the same end goal, so handling this error for the user should be okay
   • This is similar to how delete topics handles requests
3. Entity types are "Topic", "Client", and "Broker".
4. If entity_type is "Broker" and entity_name matches the broker that has received the request, read-only configs for this broker are also returned.
5. Below are the authorization requirements for each type:
   • Broker: Must be authorized to the "Describe" Operation on the "Cluster" resource
   • Topic: Must be authorized to the "Describe" Operation on the "Topic" resource
   • Client: Must be authorized to the "Describe" Operation on the "Client" resource
     • This is a new resource needed
     • TODO: best way to handle this...
6. Arbitrary configurations are allowed
   • This provides flexibility for custom clients, and allows all "plugin" or extra configs to be shown
   • The user can validate the configs after the describe command in their client to check for errors, but the wire protocol should relay all information.

ListConfigs Response (Version: 0) => [entities]   
  entities => entity_type entity_name error_code [configs]
    entity_type => INT8
    entity_name => STRING
    error_code => INT16
    configs =>
      config_name => STRING
      config_value => STRING
      read_only => BOOLEAN
      is_default => BOOLEAN

Alter Configs

AlterConfigs Request (Version: 0) => [entities] validate_only
  validate_only => BOOLEAN
  entities => entity_type entity_name error_code [configs]
    entity_type => INT8
    entity_name => STRING
    error_code => INT16
    configs =>
      config_key => STRING
      config_value => STRING

Request Semantics

1. TODO

AlterConfigs Response (Version: 0) => [responses]   
  responses => entity_type entity_name error_code
    entity_type => INT8
    entity_name => STRING
    error_code => INT16

Proposed Changes

TBD

Compatibility, Deprecation, and Migration Plan

TBD

Rejected Alternatives

TBD

Future work

• Forward requests to the relevant brokers in order to return `read-only` broker configs.