backend-common: make it possible to override service log label

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

.changeset/orange-maps-roll.md

@@ -0,0 +1,5 @@
+---
+'@backstage/backend-common': patch
+---
+
+Updated the logger created by `createRootLogger` to make it possible to override the default `service` log label.

packages/backend-common/src/logging/rootLogger.test.ts

@@ -36,12 +36,13 @@ describe('rootLogger', () => {
   });
 
   it('redacts given secrets', () => {
-    const logger = createRootLogger();
-    jest.spyOn(logger, 'write');
+    const transport = new winston.transports.Console();
+    const logger = createRootLogger({ transports: [transport] });
+    jest.spyOn(transport, 'write');
     setRootLoggerRedactionList(['SECRET-1', 'SECRET_2', 'SECRET.3']);
     logger.info('Logging SECRET-1 and SECRET_2 and SECRET.3');
 
-    expect(logger.write).toHaveBeenCalledWith(
+    expect(transport.write).toHaveBeenCalledWith(
       expect.objectContaining({
         message: 'Logging [REDACTED] and [REDACTED] and [REDACTED]',
       }),
@@ -49,12 +50,13 @@ describe('rootLogger', () => {
   });
 
   it('redacts but ignores empty and one-character secrets', () => {
-    const logger = createRootLogger();
-    jest.spyOn(logger, 'write');
+    const transport = new winston.transports.Console();
+    const logger = createRootLogger({ transports: [transport] });
+    jest.spyOn(transport, 'write');
     setRootLoggerRedactionList(['SECRET-1', 'SECRET_2', 'Q', '']);
     logger.info('Logging SECRET-1 and SECRET_2 and Q');
 
-    expect(logger.write).toHaveBeenCalledWith(
+    expect(transport.write).toHaveBeenCalledWith(
       expect.objectContaining({
         message: 'Logging [REDACTED] and [REDACTED] and Q',
       }),
@@ -125,5 +127,38 @@ describe('rootLogger', () => {
         logger.format.transform({ message: 'hello', level: 'info' }),
       ).toBeFalsy();
     });
+
+    it('can override the service label', () => {
+      const transport = new winston.transports.Console();
+      const logger = createRootLogger({ transports: [transport] });
+      const writeSpy = jest
+        .spyOn(transport, 'write')
+        .mockImplementation((_c, _e) => true);
+
+      logger.info('msg-a');
+      logger.child({ service: 'b' }).info('msg-b');
+      logger.info('msg-c', { service: 'c' });
+
+      expect(writeSpy.mock.calls).toEqual([
+        [
+          expect.objectContaining({
+            message: 'msg-a',
+            service: 'backstage',
+          }),
+        ],
+        [
+          expect.objectContaining({
+            message: 'msg-b',
+            service: 'b',
+          }),
+        ],
+        [
+          expect.objectContaining({
+            message: 'msg-c',
+            service: 'c',
+          }),
+        ],
+      ]);
+    });
   });
 });

packages/backend-common/src/logging/rootLogger.ts

@@ -101,26 +101,27 @@ export function createRootLogger(
   options: winston.LoggerOptions = {},
   env = process.env,
 ): winston.Logger {
-  const logger = winston.createLogger(
-    merge<LoggerOptions, LoggerOptions>(
-      {
-        level: env.LOG_LEVEL || 'info',
-        format: winston.format.combine(
-          winston.format(redactWinstonLogLine)(),
-          env.NODE_ENV === 'production' ? winston.format.json() : coloredFormat,
-        ),
-        defaultMeta: {
-          service: 'backstage',
+  const logger = winston
+    .createLogger(
+      merge<LoggerOptions, LoggerOptions>(
+        {
+          level: env.LOG_LEVEL || 'info',
+          format: winston.format.combine(
+            winston.format(redactWinstonLogLine)(),
+            env.NODE_ENV === 'production'
+              ? winston.format.json()
+              : coloredFormat,
+          ),
+          transports: [
+            new winston.transports.Console({
+              silent: env.JEST_WORKER_ID !== undefined && !env.LOG_LEVEL,
+            }),
+          ],
         },
-        transports: [
-          new winston.transports.Console({
-            silent: env.JEST_WORKER_ID !== undefined && !env.LOG_LEVEL,
-          }),
-        ],
-      },
-      options,
-    ),
-  );
+        options,
+      ),
+    )
+    .child({ service: 'backstage' });
 
   setRootLogger(logger);