This article explains the log collection techniques for contrail releases post 5.0

Application and systems logs can help you understand what is happening inside your cluster. The easiest and most embraced logging method for containerized applications is to write to the standard output and standard error streams. The logs are particularly useful for debugging problems and monitoring cluster activity. 

Kubectl output Format

Examples of –output-format usage

NAME                                  READY     STATUS    RESTARTS   AGE
contrail-analytics-8lsbx              5/5       Running   0          37d
contrail-analytics-zookeeper-s4xdj    1/1       Running   0          37d
contrail-analyticsdb-nodemgr-9vqbr    1/1       Running   0          37d
contrail-analyticsdb-xg76d            1/1       Running   0          37d
contrail-config-g9fn7                 5/5       Running   0          37d
contrail-config-zookeeper-swmrt       1/1       Running   0          37d
contrail-configdb-cnwzb               1/1       Running   0          37d
contrail-control-56p7r                4/4       Running   0          37d
contrail-kafka-f4xkb                  1/1       Running   0          37d
contrail-redis-pggmc                  1/1       Running   0          37d
contrail-vrouter-agent-kernel-f92x5   2/2       Running   1          37d
contrail-webui-hjgzk                  2/2       Running   0          37d
ingress-68bdd5bf66-n9n7h              1/1       Running   0          37d
ingress-error-pages-f57f86986-fb47t   1/1       Running   0          37d

Display Kubernetes logs

Everything contained in Kubernetes is represented by a RESTful resource. We refer to these resources as Kubernetes objects. Each Kubernetes object exists at a unique HTTP path.

The kubectl command makes HTTP requests to these URLs to access the Kubernetes objects that reside at these paths.

If you have multiple containers in your pod you can choose the container to view using the -c flag.

Kubernetes provides two commands for debugging running containers. The kubectl logs command downloads the current logs from the running instance:

Adding the -f flag will cause you to continuously stream logs.

The kubectl logs command always tries to get logs from the currently running container. Adding the --previous flag will get logs from a previous instance of the container. This is useful, for example, if your containers are continuously restarting due to a problem at container startup.

INFO: agent started in kernel mode
Device "vhost0" does not exist.
cat: /sys/class/net/vhost0/address: No such file or directory
INFO: creating vhost0 for nic mode: nic: ens4, mac=52:54:00:4b:b8:76
INFO: there is no ifcfg-ens4 a
nd ifcfg-vhost0, so initialize vhost0 manually
INFO: Changing physical interface to vhost in ip table
RTNETLINK answers: File exists
ERROR: failed to add address fe80::5054:ff:fe4b:b876/64 to vhost0.
INFO: set default gateway
ERROR: failed to add default gateway 10.168.6.1
INFO: set mtu
FATAL: failed to init vhost0
RTNETLINK answers: File exists

Usage:

Examples:

Kubectl output verbosity and debugging

Copying Files to and from Containers

At times you may need to copy files from a remote container to a local machine for more in-depth exploration. For example, you can use a tool like Wireshark to visualize tcpdump packet captures.  Suppose you had a file called /captures/capture3.txt inside a container in your Pod. You could securely copy that file to your local machine by running:

$ kubectl cp <pod-name> :/captures/capture3.txt ./capture3.txt

Other times you may need to copy files from your local machine into a container. Let’s say you want to copy $HOME/config.txt to a remote container. In this case, you can run: