Debugging crashes when using Finch

[shareefer]

Problem

Debugging crashes with an Init Error ImportModuleError when using Finch . Finch works fine via SAM CLI sam local invoke but SAM CLI lacks debugging capabilities.

Steps to reproduce the issue

1. Have only Finch installed.
2. Setup a Node Hello World project using SAM CLI
3. Open VS Code, setup launch.json using the VS Toolkit extension helper in the template.yaml
4. Run debugging

Expected behavior

Expected debugging to fully run through the lambda printing "Hello World" in the terminal output just as 'sam local invoke' does using Finch in the terminal.

System details (run AWS: About and/or Amazon Q: About)

• OS: MacOS 26.1 (25B78)
• Visual Studio Code version: 1.106.3 (Universal)
• AWS Toolkit version: 3.89.0
• Amazon Q version: n/a

---

Output from running Debugging

2025-12-04 10:38:13.094 [info] Starting Build use cache
2025-12-04 10:38:13.216 [info] Manifest file is changed (new hash: c0e83ff3ce1bd02a0c2a7c02974c24ec) or dependency folder (.aws-sam/deps/ab6d6894-2546-406c-a5db-a8cf1a212524) is missing for (HelloWorldFunction), downloading dependencies and copying/building source
Building codeuri: /Users/sedenfield/Documents/Gitlab/_scratchpad/sam-pod-test/sam-app/hello-world runtime: nodejs24.x architecture: arm64 functions: HelloWorldFunction
2025-12-04 10:38:13.236 [info] Running NodejsNpmBuilder:NpmPack
2025-12-04 10:38:14.744 [info] Running NodejsNpmBuilder:CopyNpmrcAndLockfile
 Running NodejsNpmBuilder:CopySource
2025-12-04 10:38:14.747 [info] Running NodejsNpmBuilder:NpmInstall
2025-12-04 10:38:15.912 [info] Running NodejsNpmBuilder:NpmTest
 Running NodejsNpmBuilder:CleanUp
2025-12-04 10:38:15.913 [info] Running NodejsNpmBuilder:CopyDependencies
2025-12-04 10:38:16.353 [info] Running NodejsNpmBuilder:CleanUpNpmrc
 Running NodejsNpmBuilder:LockfileCleanUp
2025-12-04 10:38:16.354 [info] Running NodejsNpmBuilder:LockfileCleanUp
2025-12-04 10:38:16.509 [info] Build Succeeded

Built Artifacts  : ../../../../../../../private/tmp/aws-toolkit-vscode/vsctkdda4ad74/output
Built Template   : ../../../../../../../private/tmp/aws-toolkit-vscode/vsctkdda4ad74/output/template.yaml

Commands you can use next
=========================
[*] Validate SAM template: sam validate
[*] Invoke Function: sam local invoke -t ../../../../../../../private/tmp/aws-toolkit-vscode/vsctkdda4ad74/output/template.yaml
[*] Test Function in the Cloud: sam sync --stack-name {{stack-name}} --watch
[*] Deploy: sam deploy --guided --template-file ../../../../../../../private/tmp/aws-toolkit-vscode/vsctkdda4ad74/output/template.yaml
2025-12-04 10:38:27.499 [info] Invoking app.lambdaHandler (nodejs24.x)
2025-12-04 10:38:27.733 [info] Local image was not found.
2025-12-04 10:38:27.733 [info] Removing rapid images for repo public.ecr.aws/sam/emulation-nodejs24.x
2025-12-04 10:38:27.896 [info] Building image...
2025-12-04 10:38:29.304 [info] .
2025-12-04 10:38:29.308 [info] .
2025-12-04 10:38:29.509 [info] .
2025-12-04 10:38:29.620 [info] ..
2025-12-04 10:38:29.628 [info] .
2025-12-04 10:38:29.633 [info] .
2025-12-04 10:38:29.635 [info] 
2025-12-04 10:38:29.657 [info] Using local image: public.ecr.aws/lambda/nodejs:24-rapid-arm64.
2025-12-04 10:38:29.658 [info] Mounting /tmp/aws-toolkit-vscode/vsctkdda4ad74/output/HelloWorldFunction as /var/task:ro,delegated, inside runtime container
2025-12-04 10:38:29.746 [info] SAM_CONTAINER_ID: 210a34dade7ab8ecfc09fb819b04bc6b847ee472e87c0ea7904083d0fce67920
2025-12-04 10:38:30.648 [info] START RequestId: 23d069e9-56a1-4e33-b850-192f99cc8690 Version: $LATEST
2025-12-04 10:38:30.777 [info] Debugger listening on ws://0.0.0.0:5858/0cd159e1-d8d5-44e1-8721-d9253f25346b
2025-12-04 10:38:30.779 [info] For help, see: https://nodejs.org/en/docs/inspector
2025-12-04 10:38:34.172 [info] Debugger attached.
2025-12-04 10:38:34.504 [info] 2025-12-04T18:38:34.544Z	-	ERROR	Init Error 	{"errorType":"Runtime.ImportModuleError","errorMessage":"Error: Cannot find module 'app'\nRequire stack:\n- /var/runtime/index.mjs","name":"Runtime.ImportModuleError","stack":["Runtime.ImportModuleError: Error: Cannot find module 'app'","Require stack:","- /var/runtime/index.mjs","    at loadModule (file:///var/runtime/index.mjs:577:13)","    at async UserFunctionLoader.load (file:///var/runtime/index.mjs:508:20)","    at async createRuntime (file:///var/runtime/index.mjs:1221:52)","    at async ignition (file:///var/runtime/index.mjs:1637:21)"]}
2025-12-04 10:38:34.511 [info] Waiting for the debugger to disconnect...
2025-12-04 10:38:34.575 [info] node:internal/process/promises:394
    triggerUncaughtException(err, true /* fromPromise */);
    ^

ImportModuleError [Runtime.ImportModuleError]: Error: Cannot find module 'app'
Require stack:
- /var/runtime/index.mjs
    at loadModule (file:///var/runtime/index.mjs:577:13)
    at async UserFunctionLoader.load (file:///var/runtime/index.mjs:508:20)
    at async createRuntime (file:///var/runtime/index.mjs:1221:52)
    at async ignition (file:///var/runtime/index.mjs:1637:21)

Node.js v24.11.0
2025-12-04 10:38:34.579 [info] 04 Dec 2025 18:38:34,625 [ERROR] (rapid) Init failed error=Runtime exited with error: exit status 1 InvokeID=
04 Dec 2025 18:38:34,625 [ERROR] (rapid) Invoke failed InvokeID=cc478fe9-df3f-48e0-b7c7-fe2d5365d62a error=Runtime exited with error: exit status 1
2025-12-04 10:38:34.580 [info] 04 Dec 2025 18:38:34,625 [ERROR] (rapid) Invoke DONE failed: Sandbox.Failure
2025-12-04 10:38:35.585 [info] {"errorType": "Runtime.ImportModuleError", "errorMessage": "Error: Cannot find module 'app'\nRequire stack:\n- /var/runtime/index.mjs", "trace": ["Runtime.ImportModuleError: Error: Cannot find module 'app'", "Require stack:", "- /var/runtime/index.mjs", "    at loadModule (file:///var/runtime/index.mjs:577:13)", "    at async UserFunctionLoader.load (file:///var/runtime/index.mjs:508:20)", "    at async createRuntime (file:///var/runtime/index.mjs:1221:52)", "    at async ignition (file:///var/runtime/index.mjs:1637:21)"]}
2025-12-04 10:38:35.585 [info] 
2025-12-04 10:38:36.253 [info] 
2025-12-04 10:38:36.253 [info] Command stopped: "sam local invoke"

Thank you for taking a look.

[seshubaws]

Hi @shareefer thank you for reporting this! I haven't been able to reproduce this, but it would be helpful if you could let us know if were you able to see this flow succeed using Docker?

[shareefer]

@seshubaws thank you for replying. Yes I can run this SAM App with docker with no issues

2025-12-05 10:58:41.339 [info] Starting Build use cache
2025-12-05 10:58:41.366 [info] Manifest file is changed (new hash: c0e83ff3ce1bd02a0c2a7c02974c24ec) or dependency folder (.aws-sam/deps/4466ce80-7872-4843-9224-0716986ce73b) is missing for (HelloWorldFunction), downloading dependencies and copying/building source
Building codeuri: /Users/sedenfield/Documents/Gitlab/_scratchpad/sam-pod-test/sam-app/hello-world runtime: nodejs24.x architecture: arm64 functions: HelloWorldFunction
2025-12-05 10:58:41.374 [info] Running NodejsNpmBuilder:NpmPack
2025-12-05 10:58:41.820 [info] Running NodejsNpmBuilder:CopyNpmrcAndLockfile
2025-12-05 10:58:41.821 [info] Running NodejsNpmBuilder:CopySource
2025-12-05 10:58:41.822 [info] Running NodejsNpmBuilder:NpmInstall
2025-12-05 10:58:42.454 [info] Running NodejsNpmBuilder:NpmTest
2025-12-05 10:58:42.454 [info] Running NodejsNpmBuilder:CleanUp
 Running NodejsNpmBuilder:CopyDependencies
2025-12-05 10:58:42.663 [info] Running NodejsNpmBuilder:CleanUpNpmrc
 Running NodejsNpmBuilder:LockfileCleanUp
2025-12-05 10:58:42.663 [info] Running NodejsNpmBuilder:LockfileCleanUp
2025-12-05 10:58:42.733 [info] Build Succeeded
2025-12-05 10:58:42.733 [info] Built Artifacts  : ../../../../../../../private/tmp/aws-toolkit-vscode/vsctk3bc5c69a/output
Built Template   : ../../../../../../../private/tmp/aws-toolkit-vscode/vsctk3bc5c69a/output/template.yaml

Commands you can use next
=========================
[*] Validate SAM template: sam validate
[*] Invoke Function: sam local invoke -t ../../../../../../../private/tmp/aws-toolkit-vscode/vsctk3bc5c69a/output/template.yaml
[*] Test Function in the Cloud: sam sync --stack-name {{stack-name}} --watch
[*] Deploy: sam deploy --guided --template-file ../../../../../../../private/tmp/aws-toolkit-vscode/vsctk3bc5c69a/output/template.yaml
2025-12-05 10:58:44.909 [info] Invoking app.lambdaHandler (nodejs24.x)
2025-12-05 10:58:46.036 [info] Local image is up-to-date
2025-12-05 10:58:46.045 [info] Using local image: public.ecr.aws/lambda/nodejs:24-rapid-arm64.

Mounting /tmp/aws-toolkit-vscode/vsctk3bc5c69a/output/HelloWorldFunction as /var/task:ro,delegated, inside runtime container
2025-12-05 10:58:46.093 [info] SAM_CONTAINER_ID: 5d4b2e96f0231a380391fdb2f551e8d95d1b9e0e4e3e36db60bedb21b8ada6dc
2025-12-05 10:58:46.418 [info] START RequestId: 56688f3d-a3b1-43b8-a25a-aa12a85de1eb Version: $LATEST
2025-12-05 10:58:46.458 [info] Debugger listening on ws://0.0.0.0:5858/7d4efb46-6808-4e65-8142-6f20cf834095
For help, see: https://nodejs.org/en/docs/inspector
2025-12-05 10:58:46.638 [info] Debugger attached.
2025-12-05 10:58:46.894 [info] END RequestId: cf357b7e-cda3-489c-9f4e-f1ee4466145a
REPORT RequestId: cf357b7e-cda3-489c-9f4e-f1ee4466145a	Init Duration: 0.09 ms	Duration: 469.49 ms	Billed Duration: 470 ms	Memory Size: 128 MB	Max Memory Used: 128 MB
2025-12-05 10:58:46.894 [info] {"statusCode": 200, "body": "{\"message\":\"hello world\"}"}
2025-12-05 10:58:48.003 [info] 
2025-12-05 10:58:48.003 [info] Command stopped: "sam local invoke"

[seshubaws]

Hi @shareefer thanks for providing more details, I was able to repro this. It seems that the debugging container that VSCode is creating is not mounting correctly when using Finch. It works with sam local invoke because SAM is creating a container separate from the VSCode debugging one that makes sure it works for Finch. I will surface this to the team and we will work on a fix for this!