Status
Current state: Accepted (vote thread)
Discussion thread: here (and the original discussion is here)
JIRA: - KAFKA-7433Getting issue details... STATUS
Released: 2.2
Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).
Motivation
Currently kafka-topics.sh
uses only direct Zookeeper connections which is not really desired compared to the AdminClient. This change would aim to add capability to the TopicCommand to be able to connect to a broker using the AdminClient.
This is part of KIP-4 which outlines the importance of exposing admin operations via the Kafka 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
Public Interfaces
Command-line Options
A few extra options will be added to kafka-configs.sh:
--bootstrap-server
option will be added to accept config changes. This will would accept a list of brokers that the internal AdminClient would use.
--command-config
option will be also added. This would accept a file argument that points to the AdminClient connection properties file (such as SSL, buffers, etc.).
val bootstrapServerOpt = parser.accepts("bootstrap-server", "REQUIRED: The Kafka servers to connect to, separated by commas, for instance "localhost:9091,localhost:9092". In case of providing this, a direct Zookeeper connection won't be required.") .withRequiredArg .describedAs("server to connect to") .ofType(classOf[String]) val commandConfigOpt = parser.accepts("command-config", "Property file containing connection configs to be passed to the AdminClient. " + "This is used only with --bootstrap-server option.") .withRequiredArg .describedAs("command config property file") .ofType(classOf[String])
Proposed Changes
The change proposed in this KIP is to add an extra option as stated above and to migrate create, delete, list and describe operations to use a broker connection. This would be a backward compatible change, leaving the zookeeper option available and fully working until a further point in time but would deprecate it as part of this KIP.
Specific behavior changes
- Providing
--bootstrap-server
and--zookeeper
together would result in an exception as they should be mutually exclusive. - Deleting an internal topic is allowed by the protocol and thus by this command as well. If this feature is not desirable, then ALCs must be set accordingly on the server side or the
delete.topic.enable=false
topic level config must be set.
Compatibility, Deprecation, And Migration Plan
This KIP won't implement topic config alternation as that is deprecated in the TopicCommand and should be done by kafka-configs.sh
. The only alternation we allow is changing the partition number for topics.
No other existing behavior would be removed and the implementation would be done in a backward compatible way.
Also retrieving the list of topics that are marked for deletion won't be implemented now as currently it's not possible to retrieve via any protocols. This conversation is part of KIP-142. The implementation will add a note regarding this in its output.
As part of the --zookeeper
option deprecation we will mark it as deprecated in the command help but also print out a warning message about using this deprecated option.
Test Plan
The existing tests will be run with the --bootstrap-server
mode too. Additionally we can refactor some of the kafka-topics.sh
usages in the smokes to use the AdminClient mode.
Rejected Alternatives
Protocol Changes
Topics Marked For Deletion
Currently KafkaAdminClient.describeTopics()
and KafkaAdminClient.listTopics()
uses the Metadata protocol to acquire topic information. The returned response however won't contain the topics that are under deletion but couldn't complete yet (for instance because of some replicas offline), therefore it is not possible to implement the current command's "marked for deletion" feature. To get around this there were several alternatives that can be seen below but during the discussion we decided to keep this work in KIP-142. The idea in this KIP was that we could introduce some changes in the Metadata protocol, such as:
- Cache topics that are under deletion but some of their replicas are offline.
- Create a new error, called
TOPIC__DELETION_IN_PROGRESS
- Bump the Metadata request version. The format of the protocol won't change, only the fact that there is a new Error type that we're introducing, but that requires bumping the protocol as old clients won't be able to handle it and most probably end up in an
UNKNOWN_SERVER_ERROR
. - Smarten up the
KafkaApis.handleTopicMetadataRequest
to also return the list of topics under deletion with the above error
public enum Errors { // ... TOPIC_DELETION_IN_PROGRESS(74, "Topic deletion is in progress.", TopicDeletionInProgressException::new); // ... } public class TopicDeletionInProgressException extends ApiException { private static final long serialVersionUID = 4767321103391338488L; public TopicDeletionInProgressException(String message) { super(message); } }
AlterTopics Protocol
At an early stage of the KIP discussion it occured that there is a need for a protocol that would handle topic partition changes, such as increasing the partition number. It got rejected as a similar api, called CreatePartitions already exists and we don't need a new protocol.
For archiving purposes here is the protocol:
AlterTopics Request (version: 0) => validate_only [topic_change] validate_only => BOOLEAN topic_change => topic_name target_partition_number topic_name => STRING target_partition_number => INT32 AlterTopics Response (version: 0) => throttle_time_ms [topic_change_result] throttle_time_ms => INT32 topic_change_result => topic_name error_code error_message topic_name => STRING error_code => INT16 error_message => NULLABLE_STRING
Authorization implications:
- From the authorization perspective using this protocol would require an ALTER operation on a Topic resource. Both currently available and therefore can be used.