Error handling in streams in Kafka - Step-by-Step Execution

Process Flow - Error handling in streams

Start Stream Processing

↓

Read Message from Topic

↓

Process Message

↓

Error Occurs?

No→Send Output to Next Topic

Yes↓

Handle Error

↓

Log Error

↓

Continue Processing Next Message

This flow shows how a stream reads messages, processes them, checks for errors, handles errors by logging and sending to a special topic, then continues.

Execution Sample

Kafka

try {
  process(record);
  forward(record);
} catch (Exception e) {
  log(e);
  sendToDeadLetter(record);
}

This code tries to process a record, forwards it if successful, or logs and sends it to a dead letter topic if an error occurs.

Process Table

Step	Action	Message Content	Error Occurred?	Error Handling	Output
1	Read message	valid-data-1	No	None	Process and forward
2	Process message	valid-data-1	No	None	Forwarded to next topic
3	Read message	bad-data-2	Yes	Catch exception	Send to dead letter topic
4	Log error	bad-data-2	Yes	Logged error details	No forward
5	Read message	valid-data-3	No	None	Process and forward
6	Process message	valid-data-3	No	None	Forwarded to next topic
7	End of stream	-	-	-	Stop processing

💡 Reached end of stream, no more messages to process

Status Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	After 6	Final
message	null	valid-data-1	valid-data-1	bad-data-2	bad-data-2	valid-data-3	valid-data-3	null
errorOccurred	false	false	false	true	true	false	false	false
outputTopic	empty	empty	valid-data-1	valid-data-1	valid-data-1	valid-data-1,valid-data-3	valid-data-1,valid-data-3	valid-data-1,valid-data-3
deadLetterTopic	empty	empty	empty	bad-data-2	bad-data-2	bad-data-2	bad-data-2	bad-data-2

Key Moments - 3 Insights

Why does the bad message not get forwarded to the output topic?

Because in the execution_table at step 3 and 4, the errorOccurred is true, triggering error handling that sends the message to the dead letter topic instead of forwarding.

What happens after an error is handled?

As shown in the concept_flow and execution_table, after logging and sending to dead letter, the stream continues processing the next message without stopping.

Is the stream stopped when an error occurs?

No, the stream continues as seen in the execution_table steps 5 and 6 where valid messages are processed after the error.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what is the value of 'Error Occurred?'

A No

B Unknown

C Yes

D False

💡 Hint

Check the 'Error Occurred?' column in execution_table row 3

At which step does the message get sent to the dead letter topic?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at the 'Error Handling' and 'Output' columns in execution_table rows 3 and 4

If the error handling was removed, what would happen to bad-data-2?

A It would cause the stream to stop

B It would be logged but not forwarded

C It would be forwarded to the next topic

D It would be ignored silently

💡 Hint

Refer to the concept_flow and key_moments about error handling importance

Concept Snapshot

Error handling in streams:
- Try processing each message
- If error occurs, catch exception
- Log error and send message to dead letter topic
- Continue processing next messages
- Prevents stream from stopping on errors

Full Transcript

This visual trace shows how Kafka stream processing handles errors. The stream reads messages one by one. For each message, it tries to process it. If no error occurs, the message is forwarded to the next topic. If an error happens, the stream catches the exception, logs the error, and sends the problematic message to a dead letter topic. Then the stream continues processing the next messages without stopping. This approach keeps the stream running smoothly even when some messages cause errors.