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Debug

There are many ways to debug Knative (and Kubernetes) services. And this section is not meant to describe all approaches, nor be comprehensive. Instead, I want to discuss how to access logs from deployed Knative services, since that is a generally useful first feature when debugging.

Access logs using kapp

The kapp tool is part of the comprehensive k14s Kubernetes toolset. Kapp is a generic tool for deploying and managing Kubernetes services. One of its important features is that it only requires you to just label your Kubernetes objects to enable operating on them.

Installing kapp

You can install kapp by following the instructions in get-kapp.io or downloading the latest kapp binary for your platform.

Labeling services

We will use kapp to view and tail logs from our Knative services by simply labeling them with a common label. For instance the label: knfun=demo. You can do this by passing this label (or whatever label you choose) when creating the service with kn.

kn service create watson-fn --env WATSON_API_KEY=$WATSON_API_KEY \
							--env WATSON_API_URL=$WATSON_API_URL \
							--env WATSON_API_VERSION=$WATSON_API_VERSION \
							--image docker.io/drmax/watson-fn:latest \
							--label knfun=demo

Or you can apply this label after creation by updating the service.

kn service update watson-fn --label knfun=demo

Using kapp to tail logs

Once all three services twitter-fn, watson-fn, and summary-fn have the same label, you can then use kapp to access the logs for all services at once, and even tail the logs in realtime.

kapp logs -f -a label:knfun=demo -n default --color
# waiting for 'twitter-fn-qmtyh-1-deployment-57b7d9fc6-pwc8j > user-container' logs to become available...
# waiting for 'twitter-fn-qmtyh-1-deployment-57b7d9fc6-pwc8j > queue-proxy' logs to become available...
# starting tailing 'twitter-fn-qmtyh-1-deployment-57b7d9fc6-pwc8j > user-container' logs
# starting tailing 'twitter-fn-qmtyh-1-deployment-57b7d9fc6-pwc8j > queue-proxy' logs
twitter-fn-qmtyh-1-deployment-57b7d9fc6-pwc8j > queue-proxy | {"level":"info","ts":"
...

Now, as the services are used and accessed, the window running the kapp command will continously display the output from all services. Of course, you can access the log of only one of the services at a time by labeling the service with its own label, e.g., --label knfun=twitter, and running kapp to filter only on that label.