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Status

Current state: Under Discussion

Discussion thread: here

JIRA: https://issues.apache.org/jira/browse/KAFKA-9494

PR: 

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

Motivation

The admin client allows users to describe the configuration of brokers and topics in the cluster via describeConfigs method. The returned configuration includes name, default values, source, configuration synonym including if the information is sensitive isSensitive, or is read only isReadOnly. The consumer of this API can choose to display this information in GUI e.g. web forms in Kafka lenses, Confluent Control Center. While displaying this information, fields such as  isSensitive  and isReadOnly can be used by the client to hide sensitive information and to prevent the user from editing the field respectively. This provides better upfront experience to the user. 

This KIP proposes to include additional metadata information - dataType, and documentation for individual config entries. 

The motivation behind extending the schema to include dataType of the configuration entry is to enable the client to provide better validation to the user. In the absence of dataType the only way to know if the user specified value is correct is to make an `alter` call and check if there is no error, which is a suboptimal experience.  Including the dataType could open up potentially other use cases as well.

Including documentation would enable the client to provide latest information about the config and would also act as a single source of truth.

Public Interfaces

Network protocol

Request

There is no change in the request schema except 

  1. Bump up the valid versions range
{
  "apiKey": 32,
  "type": "request",
  "name": "DescribeConfigsRequest",
  // Version 1 adds IncludeSynoyms.
  // Version 2 is the same as version 1.
  // Version 3 is the same as version 2.
  "validVersions": "0-3", <--- Updated Field
  "flexibleVersions": "none",
  "fields": [
    { "name": "Resources", "type": "[]DescribeConfigsResource", "versions": "0+",
      "about": "The resources whose configurations we want to describe.", "fields": [
      { "name": "ResourceType", "type": "int8", "versions": "0+",
        "about": "The resource type." },
      { "name": "ResourceName", "type": "string", "versions": "0+",
        "about": "The resource name." },
      { "name": "ConfigurationKeys", "type": "[]string", "versions": "0+", "nullableVersions": "0+",
        "about": "The configuration keys to list, or null to list all configuration keys." }
    ]},
    { "name": "IncludeSynoyms", "type": "bool", "versions": "1+", "default": "false", "ignorable": false,
      "about": "True if we should include all synonyms." }
  ]
}


Response

The changes to the Response schema include

  1. Bump valid versions range
  2. Add new Fields -  ConfigValueType, and Documentation
{
  "apiKey": 32,
  "type": "response",
  "name": "DescribeConfigsResponse",
  "validVersions": "0-3", <--- Updated Field
  "flexibleVersions": "none",
  "fields": [
    { "name": "ThrottleTimeMs", "type": "int32", "versions": "0+",
      "about": "The duration in milliseconds for which the request was throttled due to a quota violation, or zero if the request did not violate any quota." },
    { "name": "Results", "type": "[]DescribeConfigsResult", "versions": "0+",
      "about": "The results for each resource.", "fields": [
      { "name": "ErrorCode", "type": "int16", "versions": "0+",
        "about": "The error code, or 0 if we were able to successfully describe the configurations." },
      { "name": "ErrorMessage", "type": "string", "versions": "0+", "nullableVersions": "0+",
        "about": "The error message, or null if we were able to successfully describe the configurations." },
      { "name": "ResourceType", "type": "int8", "versions": "0+",
        "about": "The resource type." },
      { "name": "ResourceName", "type": "string", "versions": "0+",
        "about": "The resource name." },
      { "name": "Configs", "type": "[]DescribeConfigsResourceResult", "versions": "0+",
        "about": "Each listed configuration.", "fields": [
        { "name": "Name", "type": "string", "versions": "0+",
          "about": "The configuration name." },
        { "name": "Value", "type": "string", "versions": "0+", "nullableVersions": "0+",
          "about": "The configuration value." },
        { "name": "ReadOnly", "type": "bool", "versions": "0+",
          "about": "True if the configuration is read-only." },
        { "name": "IsDefault", "type": "bool", "versions": "0",
          "about": "True if the configuration is not set." },
        // Note: the v0 default for this field that should be exposed to callers is
        // context-dependent. For example, if the resource is a broker, this should default to 4.
        // -1 is just a placeholder value.
        { "name": "ConfigSource", "type": "int8", "versions": "1+", "default": "-1", "ignorable": true,
          "about": "The configuration source." },
        { "name": "IsSensitive", "type": "bool", "versions": "0+",
          "about": "True if this configuration is sensitive." },
        { "name": "Synonyms", "type": "[]DescribeConfigsSynonym", "versions": "1+", "ignorable": true,
          "about": "The synonyms for this configuration key.", "fields": [
          { "name": "Name", "type": "string", "versions": "1+",
            "about": "The synonym name." },
          { "name": "Value", "type": "string", "versions": "1+", "nullableVersions": "0+",
            "about": "The synonym value." },
          { "name": "Source", "type": "int8", "versions": "1+",
            "about": "The synonym source." }
        ]},
<--- Start of new Fields
        { "name": "ConfigValueType", "type": "int8", "versions": "3+", default": "0", "ignorable": true,
          "about": "The configuration data type. Type can be one of the following values - BOOLEAN, STRING, INT, SHORT, LONG, DOUBLE, LIST, CLASS, PASSWORD"},
        { "name": "Documentation", "type": "string", "versions": "3+", "nullableVersions": "0+",
          "about": "The configuration documentation." },
<---- End of new Fields
      ]}
    ]}
  ]
}


AdminClient Class

No new method will be added or updated to the AdminCient class. 

Proposed Changes

Under the proposed change, AdminClient.describeConfigs response (DescribeConfigsResponse.ConfigEntry) would include following new properties

  1.  Type: ConfigType - This is an Enum of all the supported data type.

    /**
 * Data type of configuration entry.
*/
public enum ConfigType {
   UNKNOWN,  
   BOOLEAN,
   STRING,
   INT,
   SHORT,
   LONG,
   DOUBLE,
   LIST,
   CLASS,
   PASSWORD
}


    ConfigType.Unknown is for ensuring backward compatibility (explained is Compatibility section below)/

    The above enum directly maps to the existing Type Enum as defined in ConfigDef.java below

     /**
 * The config types
 */
 public enum Type {
   BOOLEAN, STRING, INT, SHORT, LONG, DOUBLE, LIST, CLASS, PASSWORD
 }

      2. Documentation: String - field's documentation

DescribeConfigsResponse.ConfigEntry

public class ConfigEntry {
    private final String name;
    private final String value;
    private final ConfigSource source;
    private final boolean isSensitive;
    private final boolean isReadOnly;
    private final List<ConfigSynonym> synonyms;
    private final String type; // This is the new property
	private final String documentation; // This is the new property
.....

Rest of the changes would be plumbing this new property in AdminManager class to be eventually consumed by AdminClient class

Sample Response

 Following example show how the response would look like in JSON format. Note: Kafka uses binary protocol over TCP.

{
  "name": "offsets.topic.num.partitions",
  "value": "50",
  "source": "DEFAULT_CONFIG",
  "type": "INT",   // <---- New Field
  "synonyms": [
    {
      "name": "offsets.topic.num.partitions",
      "value": "50",
      "source": "DEFAULT_CONFIG"
    }
  ],
  "documentation": "The number of partitions for the offset commit topic (should not change after deployment)", //  <---- New Field
  "isReadOnly": true,
  "isSensitive": false,
 }


Compatibility, Deprecation, and Migration Plan

The proposed change is backward compatible in a sense that for same version of Kafka server and client response would include additional fields

For example, if one runs kafka-config.sh
bin/kafka-configs.sh --describe --entity-type brokers --bootstrap-server localhost:9092 --entity-name 0

the output would be as

replication.quota.window.num=11 type=INT sensitive=false synonyms={} documentation=...


For server version < client version type would be null

request.timeout.ms=30000 type=null sensitive=false synonyms={} documentation=null


And for server version > client version type will be ignored

request.timeout.ms=30000 sensitive=false synonyms={}

Rejected Alternatives

NA

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