Using Kowl for inspecting messages

How-to use Kowl to inspect Kafka messages

Kowl is a tool to inspect Kafka-messages structured by their topics.


How to access Kowl

  1. Open OPenLens

  2. Open the cluster whose messages you want to explore

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  3. On the left side, click on Workloads and then on Pods

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  4. you need to choose “united-manufacturing-hub” as namespace, then find the kowl-pod:

    united-manufacturing-hub-kowl-some_number

  5. Click on it, go on the right side and scroll down to Containers and then choose Ports:

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    click on the http: 8080/TCP.

    Kowl opens automatically in the browser!

How to inspect efficiently in kowl

Answer the following questions step-by-step:

  1. Are all relevant topics existing? And do they have a size larger than 0?

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    In this example, we see the weaving has some connection problem as there is no message stored under the topic /state (size = 0).

  2. Have a look at the total partitions: these shall be less than 300 max.!

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  3. Have a look at the consumer groups. Does any group have a rising lag?

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    In this case the mqtt-kafka-bridge has a little lag. But it is not rising. So it’s fine. The messages get processed.

  4. You can also open each consumer group and inspect detailed. Here you can see the lag of each topic seperated. → Find out which topic is responsible for the lag you’ve got. In case you have a rising lag.

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  5. If one topic has a rising or steady high lag, press view topic on the right side. Now you see all the messages arriving under the chosen topic. You can inspect if these are the right messages.

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  6. Press the minus between key and value in the list to get a detailed view for each message. Have a look on the header here. If there is any reason for not accepting the messages, it would be written here:

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  7. Also when positioned under topics on the left side scroll down and have a look at all the putback error topics. These shall have a size of 0. Any other number is a sign for an error. (skip this part, if you can’t see any topic named like this.)

Last modified October 5, 2022: Historian article (#107) (5f30dc0)