fix(lambda): validate logLevel with logFormat for advanced logging

packages/aws-cdk-lib/aws-lambda/README.md

@@ -173,6 +173,8 @@ new lambda.Function(this, 'Lambda', {
 });
 ```
 
+To use `applicationLogLevel` and/or `systemLogLevel` you must set `logFormat` to `LogFormat.JSON`.
+
 ## Resource-based Policies
 
 AWS Lambda supports resource-based policies for controlling access to Lambda

packages/aws-cdk-lib/aws-lambda/lib/function.ts

@@ -1085,6 +1085,10 @@ export class Function extends FunctionBase {
    * function and undefined if not.
    */
   private getLoggingConfig(props: FunctionProps): CfnFunction.LoggingConfigProperty | undefined {
+    if ((props.applicationLogLevel || props.systemLogLevel) && props.logFormat !== LogFormat.JSON) {
+      throw new Error(`To use ApplicationLogLevel and/or SystemLogLevel you must set LogFormat to '${LogFormat.JSON}', got '${props.logFormat}'.`);
+    }
+
     let loggingConfig: CfnFunction.LoggingConfigProperty;
     if (props.logFormat || props.logGroup) {
       loggingConfig = {

packages/aws-cdk-lib/aws-lambda/test/logging-config.test.ts

@@ -133,6 +133,60 @@ describe('logging Config', () => {
           logGroupName: 'customLogGroup',
         }),
       });
-    }).toThrowError('CDK does not support setting logRetention and logGroup');
+    }).toThrow(/CDK does not support setting logRetention and logGroup/);
+  });
+
+  test('Throws when applicationLogLevel is specified with TEXT logFormat', () => {
+    const app = new cdk.App();
+    const stack = new cdk.Stack(app, 'stack');
+    expect(() => {
+      new lambda.Function(stack, 'Lambda', {
+        code: new lambda.InlineCode('foo'),
+        handler: 'index.handler',
+        runtime: lambda.Runtime.NODEJS_18_X,
+        logFormat: lambda.LogFormat.TEXT,
+        applicationLogLevel: lambda.ApplicationLogLevel.INFO,
+      });
+    }).toThrow(/To use ApplicationLogLevel and\/or SystemLogLevel you must set LogFormat to 'JSON', got 'Text'./);
+  });
+
+  test('Throws when systemLogLevel is specified with TEXT logFormat', () => {
+    const app = new cdk.App();
+    const stack = new cdk.Stack(app, 'stack');
+    expect(() => {
+      new lambda.Function(stack, 'Lambda', {
+        code: new lambda.InlineCode('foo'),
+        handler: 'index.handler',
+        runtime: lambda.Runtime.NODEJS_18_X,
+        logFormat: lambda.LogFormat.TEXT,
+        systemLogLevel: lambda.SystemLogLevel.INFO,
+      });
+    }).toThrow(/To use ApplicationLogLevel and\/or SystemLogLevel you must set LogFormat to 'JSON', got 'Text'./);
+  });
+
+  test('Throws when applicationLogLevel is specified if logFormat is undefined', () => {
+    const app = new cdk.App();
+    const stack = new cdk.Stack(app, 'stack');
+    expect(() => {
+      new lambda.Function(stack, 'Lambda', {
+        code: new lambda.InlineCode('foo'),
+        handler: 'index.handler',
+        runtime: lambda.Runtime.NODEJS_18_X,
+        applicationLogLevel: lambda.ApplicationLogLevel.INFO,
+      });
+    }).toThrow(/To use ApplicationLogLevel and\/or SystemLogLevel you must set LogFormat to 'JSON', got 'undefined'./);
+  });
+
+  test('Throws when systemLogLevel is specified if logFormat is undefined', () => {
+    const app = new cdk.App();
+    const stack = new cdk.Stack(app, 'stack');
+    expect(() => {
+      new lambda.Function(stack, 'Lambda', {
+        code: new lambda.InlineCode('foo'),
+        handler: 'index.handler',
+        runtime: lambda.Runtime.NODEJS_18_X,
+        systemLogLevel: lambda.SystemLogLevel.INFO,
+      });
+    }).toThrow(/To use ApplicationLogLevel and\/or SystemLogLevel you must set LogFormat to 'JSON', got 'undefined'./);
   });
 });