Istio components are built with a flexible logging framework which provides a number of features and controls to help operate these components and facilitate diagnostics. You control these logging features by passing command-line options when starting the components.
Logging messages output by a component are categorized by scopes. A scope represents a set of related log messages which
you can control as a whole. Different components have different scopes, depending on the features the component
provides. All components have the
default scope, which is used for non-categorized log messages.
As an example, as of this writing,
istioctl has 25 scopes, representing different functional areas within the command:
Pilot-Agent, Pilot-Discovery, and the Istio Operator have their own scopes which you can discover by looking at their reference documentation.
Each scope has a unique output level which is one of:
none produces no output for the scope, and
debug produces the maximum amount of output. The default level for all scopes
info which is intended to provide the right amount of logging information for operating Istio in normal conditions.
To control the output level, you use the
--log_output_level command-line option. For example:
$ istioctl analyze --log_output_level klog:none,cli:info
In addition to controlling the output level from the command-line, you can also control the output level of a running component by using its ControlZ interface.
Log messages are normally sent to a component’s standard output stream. The
--log_target option lets you direct the output to
any number of different locations. You give the option a comma-separated list of file system paths, along with the special
stderr to indicate the standard output and standard error streams respectively.
Log messages are normally output in a human-friendly format. The
--log_as_json option can be used to force the output into JSON,
which can be easier for tools to process.
Istio control plane components can automatically manage log rotation, which make it simple to break up large logs into smaller log files.
--log_rotate option lets you specify the base file name to use for rotation. Derived names will be used for individual
--log_rotate_max_age option lets you specify the maximum number of days before file rotation takes place, while the
let you specify the maximum size in megabytes before file rotation takes place. Finally, the
--log_rotate_max_backups option lets you control
the maximum number of rotated files to keep, older files will be automatically deleted.
--log_stacktrace_level options let you control whether log information includes
programmer-level information. This is useful when trying to track down bugs in a component but is not
normally used in day-to-day operation.