Component Logging

Istio components are built with a flexible logging framework which provides a number of features and controls tohelp operate these components and facilitate diagnostics. You control these logging features by passingcommand-line options when starting the components.

Logging scopes

Logging messages output by a component are categorized by scopes. A scope represents a set of related log messages whichyou can control as a whole. Different components have different scopes, depending on the features the componentprovides. All components have the default scope, which is used for non-categorized log messages.

As an example, as of this writing, Mixer has 5 scopes, representing different functional areas within Mixer:

• adapters
• api
• attributes
• default
• grpcAdapterPilot, Citadel, and Galley 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
• error
• warning
• info
• debugwhere none produces no output for the scope, and debug produces the maximum amount of output. The default level for all scopesis 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:

$ mixs server --log_output_level attributes=debug,adapters=warning

In addition to controlling the output level from the command-line, you can also control the output level of a running componentby using its ControlZ interface.

Controlling output

Log messages are normally sent to a component’s standard output stream. The —log_target option lets you direct the output toany number of different locations. You give the option a comma-separated list of file system paths, along with the specialvalues stdout and 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.

Log rotation

Istio components can automatically manage log rotation, which make it simple to break up large logs into smaller log files.The —log_rotate option lets you specify the base file name to use for rotation. Derived names will be used for individuallog files.

The —log_rotate_max_age option lets you specify the maximum number of days before file rotation takes place, while the —log_rotate_max_size optionlet you specify the maximum size in megabytes before file rotation takes place. Finally, the —log_rotate_max_backups option lets you controlthe maximum number of rotated files to keep, older files will be automatically deleted.

Component debugging

The —log_caller and —log_stacktrace_level options let you control whether log information includesprogrammer-level information. This is useful when trying to track down bugs in a component but is notnormally used in day-to-day operation.

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Component Introspection

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