Status

Current state: Under Discussionreleased in 2.0

Discussion thread: here [Change the link from the KIP proposal email archive to your own email thread]

JIRA: JIRA 6657

Motivation

...

Kafka Streams allows to pass in different configs for different clients by prefixing the corresponding parameter with `producer.` or `consumer.`.

...

For some use cases, it's required to set different configs for different consumers. Thus, we should add two three new prefix prefixes for main, restore and global consumer. 

We might also consider to extend `KafkaClientSupplier` and add a `getGlobalConsumer()` method.

Public Interfaces

...

The changes affected classes including StreamsConfig and KafkaClientSupplier. Existing APIs look like below:

// Prefix setter for consumer config
public static final String CONSUMER_PREFIX = "consumer.";
public static String consumerPrefix(final String consumerProp) {
    return CONSUMER_PREFIX + consumerProp;
}
...
// API to get consumer configs
public Map<String, Object> getConsumerConfigs(final String groupId, final String clientId);
public Map<String, Object> getRestoreConsumerConfigs(final String clientId); 

...

// Current consumer APIs: 
Consumer<byte[], byte[]> getConsumer(final Map<String, Object> config);
Consumer<byte[], byte[]> getRestoreConsumer(final Map<String, Object> config);

Proposed Changes

We first add APIs in the StreamsConfig class to generate prefix for main consumer, restore consumer and global consumer, and functions to retrieve them as override configs:

// New Prefixes and setters for main consumer, restore consumer and global consumer
public static final String MAIN_CONSUMER_PREFIX = "main.consumer.";
public static final String RESTORE_CONSUMER_PREFIX = "restore.consumer.";
public static final String GLOBAL_CONSUMER_PREFIX = "global.consumer.";

public static String mainConsumerPrefix(final String consumerProp) {
    return MAIN_CONSUMER_PREFIX + consumerProp;
}
public static String restoreConsumerPrefix(final String consumerProp) {
    return RESTORE_CONSUMER_PREFIX + consumerProp;
}
public static String globalConsumerPrefix(final String consumerProp) {
    return GLOBAL_CONSUMER_PREFIX + consumerProp;
}
...
// API to get different types of consumer configs. 
public Map<String, Object> getMainConsumerConfigs(final String clientId);
public Map<String, Object> getRestoreConsumerConfigs(final String clientId);
public Map<String, Object> getGlobalConsumerConfigs(final String clientId); 

And add a new public API in the KafkaClientSupplier class to get global consumer during init. 

// New API for global consumer:
Consumer<byte[], byte[]> getGlobalConsumer(final Map<String, Object> config);

...

By deprecating the getConsumerConfigs function (from now user should use getMainConsumerConfigs instead), rewriting the getRestoreConsumerConfigs function and adding the getGlobalConsumerConfigs function, if one user uses restoreConsumerPrefix or globalConsumerPrefix when adding new configurations, the configs shall overwrite base consumer config. If one just wants to change main consumer behavior without actually affecting other consumers, using mainConsumerPrefix would make sure the change only apply to main consumer. If not specified, main consumer, restore consumer and global consumer shall share the same config with base consumer.

Example

if user writes:

consumer.max.poll.record = 5
main.consumer.max.poll.record = 100
restore.consumer.max.poll.record = 50

During initialization, consumers would get:

Public Interfaces

Briefly list any new interfaces that will be introduced as part of this proposal or any existing interfaces that will be removed or changed. The purpose of this section is to concisely call out the public contract that will come along with this feature.

A public interface is any change to the following:

• Binary log format

• The network protocol and api behavior

• Any class in the public packages under clientsConfiguration, especially client configuration

  • org/apache/kafka/common/serialization

  • org/apache/kafka/common

  • org/apache/kafka/common/errors

  • org/apache/kafka/clients/producer

  • org/apache/kafka/clients/consumer (eventually, once stable)

• Monitoring

• Command line tools and arguments

• Anything else that will likely break existing users in some way when they upgrade

Proposed Changes

...

Compatibility, Deprecation, and Migration Plan

• What impact (if any) will there be on existing users?
• If we are changing behavior how will we phase out the older behavior?
• If we need special migration tools, describe them here.
• When will we remove the existing behavior?

Rejected Alternatives

There is no backward compatibility issue as we are not deprecating any public API, and the underlying change should be transparent to the user.

Rejected Alternatives

NoneIf there are alternative ways of accomplishing the same thing, what were they? The purpose of this section is to motivate why the design is the way it is and not some other way.