How to protect against double money withdrawal when transferring data through Kafka?

To protect against double charging when transmitting data through Kafka, it is necessary to ensure idempotency and atomicity of message processing. Main approaches:

1. Idempotent operations — operations for debiting should be repeatable without changing the result. For example, using a unique transaction identifier and checking whether it has already been processed.

2. Storing processing state — when processing a message, save the fact of successful debiting in the database with a unique key (transactionId). If the message is received again, the operation is not repeated.

3. Using Kafka transactions (if supported) — for atomic sending and confirmation of messages.

Example in Java (simplified):

String transactionId = message.getTransactionId();
if (!database.isTransactionProcessed(transactionId)) {
    database.debitAccount(accountId, amount);
    database.markTransactionProcessed(transactionId);
}

Thus, even with repeated message delivery, the debit will occur only once.