Kafka Send a key when producing the message

Sending a Key with a Message in Apache Kafka

In Apache Kafka, it's possible to send a key along with the message when producing to a topic. The key is used by the partitioning strategy to determine the partition that the message will be sent to. The partitioning strategy is defined when the topic is created and can be either round-robin (each message is sent to the next partition in sequence) or key-based (messages with the same key are sent to the same partition).

Sending a key with a message is optional, but it can be useful for ensuring that related messages are grouped together in the same partition. This can help with certain types of processing, such as aggregation or joining data.

Here's an example in Python showing how to send a message with a key:

from kafka import KafkaProducer

producer = KafkaProducer(bootstrap_servers='localhost:9092')

key = "key1".encode('utf-8')
value = "value1".encode('utf-8')

producer.send('my-topic', key=key, value=value)
producer.flush()

In this example, the message "value1" is sent with the key "key1" to the topic "my-topic". The key and value must be encoded as bytes, so they are encoded using the utf-8 encoding. The flush method is used to ensure that the message is sent and that any buffers are flushed.

It's also possible to set the partition for a message explicitly. This can be useful in certain cases, such as when you need to ensure that related messages are sent to the same partition. To do this, you can use the partition parameter:

 

producer.send('my-topic', key=key, value=value, partition=0)

In this example, the message is sent to partition 0. If the partition parameter is not specified, the partition will be determined by the partitioning strategy.