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11_debugging_containers.md

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Debugging Containers

Accessing Local Logs

Logs of a running pod can be accessed from the Web Console or from the oc cli:

  • The Logs tab of any running pod can be used to view active logs for the current pod

  • The oc command can be used to view or tail the logs:
oc -n [-dev] logs -f <pod name>

If there is more than one container in a given pod, the -c <container-name> switch is used to specify the desired container logs.

Using a Debug Container

Objective: Create some error on app pod to start debugging: In this lab, we will scale down the database deployment so that application pods will experience errors and crash.

  • Scale down database: 
    oc -n [-dev] scale dc/mongodb-[username] --replicas=0
  • Restart rocketchat: 
    oc -n [-dev] rollout restart deployment/rocketchat-[username]
  • Once the new pod starts, notice the CrashLoopBackOff

Using the oc command to start a debug container

  • Find the name of a pod you would like to debug

    oc -n [-dev] get pods

  • Run the oc debug command to start a debug pod (your output will vary)

    $ oc -n [-dev] debug <rocketchat-pod-name>

  • Open a new separate terminal window, and view all of the containers in your debug pod using:

    oc describe pod/rocketchat-shelly-6-bm827-debug -n [-dev]

  • After this is complete, return to your debug pod terminal and run the exit command. This will remove the debug pod.

    sh-4.2$ exit
exit

Removing debug pod ...

  • Investigate the logs of your rocketchat application pod to get further information about the errors we caused by shutting down the database.

  • Resolve the crash loop backoff by scaling your database back to have 1 replica:

    oc -n [-dev] scale dc/mongodb-[username] --replicas=1

RSH and RSYNC

RSH is available to all normal pods through the web console under the Terminal tab, as well as through the oc rsh command.

  • With your choice of access, rsh into one of the application pods and test access within the namespace
    • cURL internal and external resources
    • Test internal name resolution, external name resolution, etc.
    • Explore your userid

RSYNC is also available in many pods, available through the oc rsync command.

  • On the CLI, type oc rsync -h
  • Using this command, copy the contents of the mongo data directory to your local machine, or from your machine to the remote pod

Port Forwarding

The oc port-forward command enables users to forward remote ports running in the cluster into a local development machine.

  • Find your pod and use the port forward command
oc -n [-dev] get pods  | grep rocketchat-[username]
oc -n [-dev] port-forward [pod name from above] 8000:3000

Next page - Logging and Visualizations