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 Adopted

Discussion thread: TBD here

JIRA: 

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 few specific use cases are worth pointing out:

1. The Metadata request exposes topic metadata, but it does not expose topic configs. ListConfigs DescribeConfigs will make that information available to any client of the Kafka protocol and the AdminClient will expose it to normal users.
2. AlterConfigs would make it possible to update topic configs, but also client and replication quotas via the protocol and the AdminClient.
3. One should be able to tell how a topic or broker is configured including defaults and overrides.

Public Interfaces

ACLs

A new ACL resource type `Configs` will be introduced with Describe, Alter and All operations. Initially, this resource type will work at a global level like the Cluster resource type. That is, the only valid resource name will be "kafka-cluster". This leaves the door open for evolving this to be more fine-grained in the futureWe will introduce 2 new ACL operations: DescribeConfigs and AlterConfigs. These operations apply to resources that have configs (i.e. Broker and Topic). In addition, DescribeConfigs/AlterConfigs on the Cluster resource allows one to read and write configs on any resource with configs. Finally, the DescribeConfigs and AlterConfigs operations are included in the `All` operation.

Protocol APIs

Wire Format types

Entity types will be encoded to INT8 in the following way:

• -2: Unknown
• -1: Any (for filtering, but currently unused)
• 0: Broker
• 1: Topic
• 2: Client

KIP-140: Add administrative RPCs for adding, deleting, and listing ACLs introduced a wire format representation for ResourceType and AclOperation. We weill add new values to both types as follows:

AclOperation

• 0: Unknown

• 1: Any

• 2: All

• 3: Read

• 4: Write

• 5: Create

• 6: Delete

• 7: Alter

• 8: Describe

• 9: ClusterAction

• 10: DescribeConfigs (new)

• 11: AlterConfigs (new)

ResourceType

• 0: Unknown

• 1: Any

• 2: Topic

• 3: Group

• 4: Cluster

• 5: Broker (new)

Describe

...

Configs

ListConfigsDescribeConfigs Request (Version: 0) => [entitiesresource [config_name]]   
  entitiesresource => entityresource_type entityresource_name
    entityresource_type => INT8
    entityresource_name => STRING
  config_name => STRING

Request semantics:

1. Can be sent to any broker
2. If there are multiple instructions for the same entity resource in one request the extra request will be ignored
   • This is because the list of entities resources is modeled server side as a set
   • Multiple entities resources 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. If the config_name array is null, all configs are returned. Otherwise, configs with the provided names are returned.
4. Valid resource Entity types are "Topic" , "Client", and "Broker".
5. If entityresource_type is "Broker" and entity, the resource_name matches must be the id of the broker that has received processing the request as the brokers don't have any dynamic configs currently (apart from replication quotas configs, which are excluded). All broker configs are read-only. Conversely, there are no read-only topic configs for this broker are also returned.
6. The principal must be authorized to "Describe" the "Configs" resource type or "Describe" the "Cluster" resource type. Unauthorized requests will receive a ConfigsAuthorization error code.
7. at the moment.
8. Replication, User and Client Quota configs are not supported. See "Future work" for more details.
9. Authorization is as follows:
   1. Topic configs: "DescribeConfigs" on the "Topic" or "Cluster" resource ("DescribeConfigs" is also included in the "All" operation). Unauthorized requests will receive an appropriate AuthorizationFailed error code.
   2. Broker configs: "DescribeConfigs" on the "Broker" or "Cluster" resource ("DescribeConfigs" is also included in the "All" operation). Unauthorized requests will receive an appropriate AuthorizationFailed error code.
10. Errors are reported independently per resource.

ListConfigsDescribeConfigs Response (Version: 0) => error_code [entities]
  error_codeentities => INT16
  entities => entityerror_code resource_type entityresource_name [configs]
	error_code    entity=> INT16
	resource_type => INT8
    entityresource_name => STRING
    configs =>
      config_name => STRING
      config_value => STRING
      read_only => BOOLEAN
      is_default => BOOLEAN
      is_sensitive => BOOLEAN

Alter Configs

AlterConfigs Request (Version: 0) => [entitiesresources] validate_only
  validate_only => BOOLEAN
  entitiesresources => entityresource_type entityresource_name [configs]
    entityresource_type => INT8
    entityresource_name => STRING
    configs =>
      config_name => STRING
      config_value => STRING

...

1. Can be sent to any broker
2. If there are multiple instructions for the same entity in resource in one request, an InvalidRequestException will be logged on the broker and a single error code for that topic will be returned to the client
   • This is because the list of entities resources is modeled server side as a map with entity as the resource as the key
3. Entity Valid resource types are "Topic", " Client", and "Broker".
4. The principal must be authorized to "Alter" the "Configs" resource type or "Alter" the "Cluster" resource type. Unauthorized requests will receive a ConfigsAuthorization for all entities.
5. However, since all broker configs are currently read_only, only the former makes sense until that changes.
6. If an Alter operation is attempted on a read-only config, an UnsupportedOperation error will be returned for the relevant resource.
7. Authorization is as follows:
   1. Topic configs: "AlterConfigs" on the "Topic" or "Cluster" resource ("AlterConfigs" is also included in the "All" operation). Unauthorized requests will receive an appropriate AuthorizationFailed error code.
   2. Broker configs: "AlterConfigs" on the "Broker" or "Cluster" resource ("AlterConfigs" is also included in the "All" operation). Unauthorized requests will receive an appropriate AuthorizationFailed error code.
8. Replication, User and Client Quota configs are not supported. See "Future work" for more detailsIf an Alter operation is attempted on a read-only config, an UnsupportedOperation error will be returned for the relevant entity.
9. The request is not transactional. 
   1. If an error occurs for an entityresource, others could still be updated.
   2. Errors are reported independently per entityresource.
10. For tools that allow users to alter configs, a validation/dry-run mode where validation errors are reported but no creation is attempted is available via the validate_only parameter.

AlterConfigs Response (Version: 0) => [responses]   
  responses => entityresource_type entityresource_name error_code error_message
    entity	resource_type => INT8
    entity	resource_name => STRING
    error_code => INT16
    error_message => NULLABLE_STRING

Policy

In a similar fashion to KIP-108: Create Topic Policy, we allow users to define a policy class to validate alter configs requests. The config name will be alter.configs.policy.class.name and the interface follows:

package org.apache.kafka.server.policy;
 
enum ConfigEntityType {
    CLIENT, BROKER, TOPIC, UNKNOWN;
}

public interface AlterConfigsPolicy extends Configurable, AutoCloseable {

    /**
     * Class containing the create request parameters.
     */
    class RequestMetadata {
        /**
         * Create an instance of this class with the provided parameters.
         *
         * This constructor is public to make testing of <code>AlterConfigPolicy</code> implementations easier.
         */
        public RequestMetadata(ConfigEntityTypeConfigResource entityTyperesource, String entityName, Map<String, String> configsConfig config) { ... }

        /**
         * Return the configsConfig in the request.
         */
        public Map<String, String> configsConfig config() { ... }
    }

    /**
     * Validate the request parameters and throw a <code>PolicyViolationException</code> with a suitable error
     * message if the alter configs request parameters for the provided entityresource do not satisfy this policy.
     *
     * Clients will receive the POLICY_VIOLATION error code along with the exception's message. Note that validation
     * failure only affects the relevant entityresource, other entityresources in the request will still be processed.
     *
     * @param requestMetadata the alter configs request parameters for the provided entityresource.
     * @throws PolicyViolationException if the request parameters do not satisfy this policy.
     */
    void validate(RequestMetadata requestMetadata) throws PolicyViolationException;
}

Users will have to ensure that the policy implementation code is in the broker's classpath. Implementations should throw the existing PolicyViolationException with an appropriate error message if the request does not fulfill the policy requirements. We chose a generic name for the only parameter of the validate method in case we decide to add parameters that are not strictly related to the topic (e.g. session information) in the future. The constructor of RequestMetadata is public to make testing convenient for users. Under normal circumstances, it should only be instantiated by Kafka. We chose to create separate API classes instead of reusing request classes to make it easier to evolve the latter.

AdminClient APIs

Proposed Changes

They follow a similar pattern as existing AdminClient APIs:

public class AdminClient {
    public DescribeConfigsResult describeConfigs(Collection<ConfigResource> resources, DescribeConfigsOptions options);
    public AlterConfigsResult alterConfigs(Map<ConfigResource, Config> configs, AlterConfigsOptions options);
}

public class DescribeConfigsOptions { 
    public DescribeConfigsOptions timeoutMs(Integer timeout);
}

public class DescribeConfigsResult {
    public Map<ConfigResource, KafkaFuture<Config>> results()
    public KafkaFuture<Map<ConfigResource, Config>> all();
}
 
public class AlterConfigsOptions { 
    public AlterConfigsOptions timeoutMs(Integer timeout);
	public AlterConfigsOptions validateOnly(boolean validateOnly);
}

public class AlterConfigsResult {
    public KafkaFuture<Void> all();
    public Map<ConfigResource, KafkaFuture<Void>> results();
}
 
public class ConfigResource {
    enum Type {
		BROKER, TOPIC, UNKNOWN;
    }
 
    public ConfigResource(Type type, String name) { ... }
    
    public Type type() { ... }
    public String name() { ... }
}

 
public class Config {
    public Config(Collection<ConfigEntry> configs) { ... }
    public Collection<ConfigEntry> entries() { ... }
    public Config get(String name) { ... }
}
public class ConfigEntry {
    public ConfigEntry(String name, String value) {
        this(name, value, false, false, false);
    }
    public ConfigEntry(String name, String value, boolean isDefault, boolean isSensitive, boolean isReadOnly) { ... }
    public String name() { ... }
    public String value() { ... }
    public boolean isDefault { ... }
    public boolean isSensitive { ... }
    public boolean isReadOnly { ... }
}

Proposed Changes

In addition to what is mentioned in the "Public Interfaces" section, it's worth mentioning that the describeConfigs implementation will perform requests to min(1, N) brokers where N is the number of ConfigResources that have a Broker resource type.TBD

Compatibility, Deprecation, and Migration Plan

Authorization...

Rejected Alternatives

We are adding new ACL Operations and a new ACL Resource Type, so third-party Authorizer implementations will potentially have to be updated in order to support them. Since this only affects newly introduced protocol and AdminClient APIs, it's not a compatibility issue. It simply means that the new functionality won't be available for users of such Authorizer implementations until they are updated.

With regards to forwards compatibility, ConfigResource.Type has an UNKNOWN element in case it receives data from a newer broker that cannot be mapped to one of the existing enum types.

Rejected Alternatives

1. Allowing sensitive data to be returned: it's good security practice to never expose sensitive data. If necessary, the user can reset the relevant sensitive data (e.g. a password).
2. Introducing a new Configs resource instead of DescribeConfigs and AlterConfigs operations: there is always a one to one mapping between a resource and its configs, so there isn't much value in creating a separate resource for Configs. By adding new operations to existing resources, it's easier to see all the ACLs that affect a given resource.

...

Future work

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

...

1. Support for reading and updating client, user and replication quotas. We initially included that in the KIP, but it subsequently became apparent that a separate protocol and AdminClient API would be more appropriate. The reason is that client/user quotas can be applied on a client id, user or (client id, user) tuple. In the future, the hierarchy may get even more complicated. So, it makes sense to keeping the API simple for the simple cases while introducing a more sophisticated API for the more complex case.