Logging

Broadly, there are two types of logs you may be interested in. On cluster or node level; for the applications you are running inside your cluster, and at an infrastructure level, the applications which are responsible for running the cluster itself. As the Charmed Distribution of Kubernetes^® is pure Kubernetes, you can use any of the tools and techniques to examine cluster logs as described in the Kubernetes documentation.

For the infrastructure, your CDK deployment has centralised logging set up as default. Each unit in your cluster automatically sends logging information to the controller based on the current logging level. You can use the Juju command line to easily inspect these logs and to change the logging level, as explained below.

Viewing logs

To view the logs from the current controller and model, simply run:

juju debug-log

The default behaviour is to show the last 10 entries and to tail the log (so you will need to terminate the command with Ctrl-C).

The output is in the form:

<entity> <timestamp> <log-level> <module>[:<line-no>] <message>

For example, a typical line of output might read:

unit-kubernetes-master-0: 18:04:11 INFO juju.cmd running jujud [2.4.2 gc go1.10]

The entity is the unit, machine or application the message originates from (in this case kubernetes-master/0). It can be very useful to filter the output based on the entity or log level, and the debug-log command has many options.

For a full description, run the command juju help debug-log or see the Juju documentation. Some useful examples are outlined below.

Useful examples

View the last 100 entries and tail the log:

juju debug-log -n 100

Show the last 20 entries and exit:

juju debug-log -n 20 --no-tail

Replay the log from the very beginning, but filter to logs from kubernetes-worker/0:

juju debug-log --replay --include=kubernetes-worker/0

Viewing logs on a machine

If it becomes necessary for any reason, it is also possible to view logs directly on the running machine. A user with SSH access can connect to the relevant machine and find the logs for all the units running on that machine in the directory /var/logs/juju. The juju ssh command can be used for this, and you can connect to the relevant machine using a unit identifier. So for example, to look at the logs on the machine running the first unit of kubernetes-worker you can run the following:

juju ssh kubernetes-worker/0
ls /var/logs/juju/

Which should show something similar to:

machine-1.log  machine-lock.log  unit-flannel-1.log  unit-kubernetes-worker-0.log

Note that the logs from other units (in this case ‘flannel’) running on this machine can also be found here.

Logging level

You can check the current logging level by running the command:

juju model-config logging-config

This will result in output similar to:

<root>=WARNING;unit=DEBUG

…which is the default for any Juju model. This indicates that the machine log level is set to ‘WARNING’, and the unit logging level is set to ‘DEBUG’. As all the software components of your kubernetes cluster run in units, these logs are likely to be useful for diagnosing issues with software.

The logging levels, from most verbose to least verbose, are as follows:

• TRACE
• DEBUG
• INFO
• WARNING
• ERROR

The logging level can be set like this:

 juju model-config logging-config="<root>=WARNING;unit=TRACE"

…which in this case sets the logging level for all units to TRACE

Additional information

As previously mentioned, you can see more detailed information on accessing the logs from your cluster in the Juju documentation, including the following:

• Altering the agent logging setup
• Setting up remote logging
• More advanced filtering and additional examples