Skip to main content
Version: Next

Debug Pulsar Functions

This document describes how to debug Pulsar functions through Pod logs, log topics, and pulsar-admin commands.

Use Pod logs

Logs in Kubernetes give you insight into resources such as nodes, Pods, containers, deployments and replica sets. This insight allows you to observe the interactions between those resources and see the effects that one action has on another. Pod logs record events happening in a cluster, which can be very useful for debugging. Before debugging a Pod, you need to ensure the Pod is already scheduled and running.

The built-in way to check logs on your Kubernetes cluster is with kubectl CLI commands. You can use the kubectl logs pod POD_NAME -n NAMESPACE_NAME to check logs of the affected container. In addition, you can use kubectl logs pod POD_NAME -n NAMESPACE_NAME --previous to retrieve logs from a previous instantiation of a container.

In addition, you can use the following command to check the specific Pod.

  • kubectl get pod POD_NAME -n NAMESPACE_NAME: check Pod status.

  • kubectl describe pod POD_NAME -n NAMESPACE_NAME: check the current state of the Pod and recent events.

For the use of kubectl commands, see kubectl command reference.

Use log topic

In Pulsar Functions, you can generate log information defined in functions to a specified log topic. You can configure consumers to consume messages from a specified log topic to check the log information.

Pulsar Functions core programming model


import org.apache.pulsar.functions.api.Context;
import org.apache.pulsar.functions.api.Function;
import org.slf4j.Logger;

public class LoggingFunction implements Function<String, Void> {
public void apply(String input, Context context) {
Logger LOG = context.getLogger();
String messageId = new String(context.getMessageId());

if (input.contains("danger")) {
LOG.warn("A warning was received in message {}", messageId);
} else {"Message {} received\nContent: {}", messageId, input);

return null;

As shown in the example above, you can get the logger via context.getLogger() and assign the logger to the LOG variable of slf4j, so you can define your desired log information in a function using the LOG variable. Meanwhile, you need to specify the topic to which the log information is produced.

  • This example shows how to specify the log topic through the CRD.

    kind: Function
    name: java-function-sample
    namespace: default
    className: exclamation_function.ExclamationFunction
    forwardSourceMessageProperty: true
    maxPendingAsyncRequests: 1000
    replicas: 1
    maxReplicas: 5
    logTopic: persistent://public/default/logging-function-logs
    - persistent://public/default/java-function-input-topic
    typeClassName: java.lang.String
    topic: persistent://public/default/java-function-output-topic
    typeClassName: java.lang.String
    # Other function configs
  • This example shows how to specify the log topic through the pulsar-admin CLI tool.


    To use the pulsar-admin CLI tool to monitor Pulsar functions and connectors, you should start Function Mesh Worker service in advance. For details, see work with pulsar-admin CLI tool.

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

Use pulsar-admin CLI tool

To debug a Pulsar function, you can perform the following operations.

For more information, see Pulsar Functions CLIs.


The pulsar-admin functions get command is used to get information about a Pulsar Function.

pulsar-admin functions get options


The pulsar-admin functions list command is used to lists all running Pulsar functions.

pulsar-admin functions list options


The pulsar-admin functions status command is used to check the current status of a Pulsar function.

pulsar-admin functions status options


The pulsar-admin functions stats command is used to get the current stats of a Pulsar Function.

pulsar-admin functions stats options


The pulsar-admin functions trigger command is used to trigger a specified Pulsar Function with a supplied value. This command simulates the execution process of a Pulsar Function and verifies it.