Root Logger Service

Root Logger

The root logger is the logger that is used by other root services. It's where the implementation lies for creating child loggers around the backstage ecosystem including child loggers for plugins with the correct metadata and annotations.

If you want to override the implementation for logging across all of the backend, this is the service that you should override.

Configuring the service

Configuration parameters

The Root Logger Service can be configured with the backend.logger section of your app-config.yaml.

The following parameters are available:

• level (string, optional): Sets the global log level. Possible values are debug, info, warn, or error. Only messages at or above this level will be logged. This can also be set via the LOG_LEVEL environment variable, which takes precedence. Defaults to info. See Modifying the log level.

• meta (object, optional): Additional metadata to include with every log entry.

• overrides (array, optional): Allows to specify logger overrides for specific plugins or messages. Each override can match on plugin names, message patterns, or any field contained in the log, and set a custom log level for those matches.

Log level overrides are useful for controlling the volume of logs generated in Backstage. They allow you to apply a global log level, info for example, while setting a stricter level, such as warn, for specific verbose plugins.

The reverse is also possible: you can set a global log level of warn while enabling a more detailed level, such as debug, for certain logs.

Example:

backend:
  logger:
    meta:
      env: prod # Every log message will have `env="prod"`

    level: info # Set the global log level to info (the default)

    overrides:
      # Set the log level to 'debug' for the catalog plugin logs
      - matchers:
          plugin: catalog
        level: debug

      # Ignore 'info' incoming HTTP requests logs from the rootHttpRouter service
      - matchers:
          service: rootHttpRouter
          type: incomingRequest
        level: warn

      # Ignore logs starting with "Task worker starting", unless they're warnings or errors
      - matchers:
          message: ['/^Task worker starting/']
        level: warn

Modifying the log level

The available log levels, in order of decreasing verbosity, are:

• debug: Detailed information, typically useful only when troubleshooting.
• info: General information about the application's operation. This is the default level.
• warn: Indicates potential issues or situations that may require attention.
• error: Indicates errors that have occurred but may not necessarily prevent the application from continuing.

The verbosity of the logging can be controlled by setting the log level. The log level determines the minimum severity level of events that will be output to the console. For example, if the log level is set to info, events with a severity level of debug will be ignored.

To increase the log level, you can set the LOG_LEVEL environment variable to a higher severity level, such as warn or error. However, be aware that increasing the log level might not result in more output if the existing code primarily emits logs at lower severity levels (e.g., debug or info). In such cases, you may need to adjust the logging statements within the code to use higher severity levels to see more output.

No additional steps are required beyond setting the LOG_LEVEL environment variable, but the effectiveness depends on the existing logging statements in the code.

To learn more, see the Debugging Backstage guide.

Overriding the default implementation

The following example is how you can override the root logger service to add additional metadata to all log lines.

import { coreServices } from '@backstage/backend-plugin-api';
import { WinstonLogger } from '@backstage/backend-defaults/rootLogger';
import { createConfigSecretEnumerator } from '@backstage/backend-defaults/rootConfig';

const backend = createBackend();

backend.add(
  createServiceFactory({
    service: coreServices.rootLogger,
    deps: {
      config: coreServices.rootConfig,
    },
    async factory({ config }) {
      const logger = WinstonLogger.create({
        meta: {
          service: 'backstage',
          // here's some additional information that is not part of the
          // original implementation
          podName: 'myk8spod',
        },
        level: process.env.LOG_LEVEL || 'info',
        format:
          process.env.NODE_ENV === 'production'
            ? format.json()
            : WinstonLogger.colorFormat(),
        transports: [new transports.Console()],
      });

      const secretEnumerator = await createConfigSecretEnumerator({
        logger,
      });
      logger.addRedactions(secretEnumerator(config));
      config.subscribe?.(() => logger.addRedactions(secretEnumerator(config)));

      return logger;
    },
  }),
);