Dev: Logging in odo

odo uses Klog for V style logging.

Logging categories

Each logging output is categorizes into logging levels.

Logging value	Output
V(0)	General information
V(1)	Experimental debugging output / testing suite
V(2)	Devfile debugging output
V(3)	Kubernetes and OpenShift client debugging output
V(4)	Generic debugging information
V(10)	Kubernetes and OpenShift HTTP library debugging output

Working

Every odo command takes an optional flag -v that must be used with an integer log level in the range from 0-9. Any INFO severity log statement that is logged at a level lesser than or equal to the one passed with the command alongside -v flag will be logged to STDOUT.

Alternatively, environment variable ODO_LOG_LEVEL can be used to set the verbosity of the log level in the integer range 0-9. The value set by ODO_LOG_LEVEL can be overridden by explicitly passing the -v command line flag to the odo command, in such an event -v flag takes precedence over the environment variable ODO_LOG_LEVEL.

All ERROR severity level log messages will always be logged regardless of the values of v or ODO_LOG_LEVEL.

In order to list multiple log levels, you can provide --vmodule to odo. --vmodule takes a key=value command-delimited output. For example: --vmodule "*=1,*=2,*=3" to list log levels 1, 2 and 3 for all files (*), while --vmodule "occlient=3" would list all 3 level log messages in the occlient folder.

Usage

Every source file that requires logging will need to import klog:

import "k8s.io/klog"

Any default debug level severity messages need to be logged using:

klog.V(4).Infof(msg, args...)

For more information on level logging conventions please refer here.

Error messages can be logged as under:

klog.Errorf(msg, args...)

Warning messages can be logged as under:

klog.Warningf(msg, args...)

In addition to the above logging, the following hidden flags are available for debugging:

--add_dir_header                   If true, adds the file directory to the header
--alsologtostderr                  Log to standard error as well as files
--log_backtrace_at traceLocation   When logging hits line file:N, emit a stack trace (default :0)
--log_dir string                   If non-empty, write log files in this directory
--log_file string                  If non-empty, use this log file
--log_file_max_size uint           Defines the maximum size a log file can grow to. Unit is megabytes. If the value is 0, the maximum file size is unlimited. (default 1800)
--logtostderr                      Log to standard error instead of files (default true)
--skip_headers                     If true, avoid header prefixes in the log messages
--skip_log_headers                 If true, avoid headers when opening log files
--stderrthreshold severity         Logs at or above this threshold go to stderr (default 2)