How to ensure that Kafka readers receive messages in the same order in which they were written?

To ensure that Kafka readers receive messages in the same order they were written, consider the following points:

• Use the same partition for related messages. The message order is guaranteed only within a single partition.
• Use message keys. When sending messages with the same key, Kafka will direct them to the same partition, preserving order.
• Read from the partition sequentially. The consumer should process messages from the partition in order of their offset.

Example in C# using Confluent.Kafka:

var config = new ConsumerConfig
{
    GroupId = "my-group",
    BootstrapServers = "localhost:9092",
    AutoOffsetReset = AutoOffsetReset.Earliest
};

using var consumer = new ConsumerBuilder<Ignore, string>(config).Build();
consumer.Subscribe("my-topic");

while (true)
{
    var consumeResult = consumer.Consume();
    Console.WriteLine($"Received message at offset {consumeResult.Offset}: {consumeResult.Message.Value}");
    // Process messages in the order they are received
}

Important: If you have multiple partitions, the order is guaranteed only within each partition, not across them.