Debug with log topic

When using Pulsar Functions, you can generate logs predefined in functions to a specified log topic and configure consumers to consume messages from the log topic.

For example, the following function logs either a WARNING-level or INFO-level log based on whether the incoming string contains the word danger or not.

  1. import org.apache.pulsar.functions.api.Context;
  2. import org.apache.pulsar.functions.api.Function;
  3. import org.slf4j.Logger;
  5. public class LoggingFunction implements Function<String, Void> {
  6.     @Override
  7.     public void apply(String input, Context context) {
  8.         Logger LOG = context.getLogger();
  9.         String messageId = new String(context.getMessageId());
  11.         if (input.contains("danger")) {
  12.             LOG.warn("A warning was received in message {}", messageId);
  13.         } else {
  14.             LOG.info("Message {} received\nContent: {}", messageId, input);
  15.         }
  17.         return null;
  18.     }
  19. }

As shown in the example, you can get the logger via context.getLogger() and assign the logger to the LOG variable of slf4j, so you can define your desired logs in a function using the LOG variable.

Meanwhile, you need to specify the topic that the logs can be produced to. The following is an example.

  1. bin/pulsar-admin functions create \
  2.   --log-topic persistent://public/default/logging-function-logs \
  3.   # Other function configs

The message published to a log topic contains several properties:

  • loglevel: the level of the log message.
  • fqn: the fully qualified function name that pushes this log message.
  • instance: the ID of the function instance that pushes this log message.