Can not use local ipykernel

[lfriedri]

Description

I want to setup an ipykernel in my own process and then use jupyter server to provide this kernel to VS code. However, the jupyter server does not recognize the running ipykernel, even though, I use allow_external_kernels=True and give the directory with the existing kernel connection file with external_connection_dir.

Reproduce

1. Start ipykernel with the following code:
   from ipykernel import kernelapp app = kernelapp.IPKernelApp.instance() app.initialize() app.start()
2. Commandline gives the name of the kernel connection file (kernel-34228.json)
3. Confirm that kernel connection file exists in C:\portable_programs\winpython3.12\settings\runtime
4. Confirm that ipykernel is available by running
   jupyter console --existing kernel-34228.json
5. Start jupyter server by
   jupyter server --ServerApp.allow_external_kernels=True --ServerApp.external_connection_dir=C:\portable_programs\winpython3.12\settings\runtime
6. Connect to jupyter server with VS code jupyter extension
7. jupyter server console reports the starting of a new kernel, which can also be seen in the runtime directory.

Expected behavior

jupyter server recognizes the running ipykernel and provides option to connect to it, instead of starting a new kernel.

Context

• Operating System and version: Windows 11
• Jupyter Server version: jupyter_server==2.16.0
• ipykernel==6.29.5
• python 3.12
• VS code version 1.100.2
• VS code jupyter extension version 2025.5.0

Troubleshoot Output

C:\portable_programs\winpython3.12\scripts>jupyter troubleshoot
$PATH:
        C:\portable_programs\winpython3.12\python-3.12.0.amd64\Lib\site-packages\PyQt5
        C:\portable_programs\winpython3.12\python-3.12.0.amd64\Lib\site-packages\PySide2
        C:\portable_programs\winpython3.12\python-3.12.0.amd64\
        C:\portable_programs\winpython3.12\python-3.12.0.amd64\DLLs
        C:\portable_programs\winpython3.12\python-3.12.0.amd64\Scripts
        C:\portable_programs\winpython3.12\python-3.12.0.amd64\..\t
        C:\portable_programs\winpython3.12\python-3.12.0.amd64\..\t\Julia\bin
        C:\portable_programs\winpython3.12\python-3.12.0.amd64\..\n
        C:\WINDOWS\system32
        C:\WINDOWS
        C:\WINDOWS\System32\Wbem
        C:\WINDOWS\System32\WindowsPowerShell\v1.0\
        C:\WINDOWS\System32\OpenSSH\
        C:\Program Files (x86)\Symantec\VIP Access Client\
        C:\Program Files (x86)\Plantronics\Spokes3G\
        C:\Program Files\Git\cmd
        C:\Program Files\dotnet\
        C:\Program Files\nodejs\
        C:\Program Files\TortoiseHg\
        C:\Users\lars friedrich\AppData\Local\Microsoft\WindowsApps
        C:\Users\lars friedrich\AppData\Roaming\npm
        C:\Users\lars friedrich\AppData\Local\Programs\MiKTeX\miktex\bin\x64\
        C:\Users\lars friedrich\.dotnet\tools
sys.path:

C:\portable_programs\winpython3.12\python-3.12.0.amd64\Scripts\jupyter-troubleshoot.EXE

C:\local_data\rndthon4all

C:\local_data\rndthon4all\optopy

C:\portable_programs\winpython3.12\python-3.12.0.amd64\python312.zip

C:\portable_programs\winpython3.12\python-3.12.0.amd64\DLLs

C:\portable_programs\winpython3.12\python-3.12.0.amd64\Lib

C:\portable_programs\winpython3.12\python-3.12.0.amd64

C:\portable_programs\winpython3.12\python-3.12.0.amd64\Lib\site-packages

C:\portable_programs\winpython3.12\python-3.12.0.amd64\Lib\site-packages\win32

C:\portable_programs\winpython3.12\python-3.12.0.amd64\Lib\site-packages\win32\lib

C:\portable_programs\winpython3.12\python-3.12.0.amd64\Lib\site-packages\Pythonwin
sys.executable:

C:\portable_programs\winpython3.12\python-3.12.0.amd64\python.exe
sys.version:

3.12.0 (tags/v3.12.0:0fb18b0, Oct  2 2023, 13:03:39) [MSC v.1935 64 bit (AMD64)]
platform.platform():

Windows-11-10.0.26100-SP0
where jupyter:

C:\portable_programs\winpython3.12\python-3.12.0.amd64\Scripts\jupyter.exe
pip list:

Package                   Version

------------------------- --------------

absl-py                   2.2.0

aiofiles                  24.1.0

aiohappyeyeballs          2.4.6

aiohttp                   3.11.12

aiosignal                 1.3.2

annotated-types           0.7.0

anyio                     4.8.0

apptools                  5.3.0

argon2-cffi               23.1.0

argon2-cffi-bindings      21.2.0

arrow                     1.3.0

asttokens                 2.4.1

astunparse                1.6.3

async-lru                 2.0.5

async-timeout             5.0.1

attrs                     24.3.0

Automat                   24.8.1

babel                     2.17.0

bcrypt                    4.2.0

beautifulsoup4            4.13.4

bidict                    0.23.1

bleach                    6.2.0

blinker                   1.9.0

blosc2                    2.7.1

cellpose                  3.0.8

certifi                   2024.12.14

cffi                      1.17.1

chardet                   5.2.0

charset-normalizer        3.4.1

click                     8.1.7

clr-loader                0.2.6

colorama                  0.4.6

comm                      0.2.2

comtypes                  1.4.7

configobj                 5.0.9

constantly                23.10.4

contourpy                 1.3.0

cryptography              43.0.1

cycler                    0.12.1

dash                      2.18.2

dash-core-components      2.0.0

dash-html-components      2.0.0

dash-table                5.0.0

debugpy                   1.8.6

decorator                 5.1.1

defusedxml                0.7.1

docutils                  0.21.2

enum-compat               0.0.3

envisage                  7.0.4

et-xmlfile                1.1.0

executing                 2.1.0

fastapi                   0.115.8

fastjsonschema            2.21.1

fastremap                 1.16.1

filelock                  3.17.0

fill_voids                2.0.8

fire                      0.7.0

Flask                     3.0.3

flatbuffers               25.2.10

fonttools                 4.54.1

fqdn                      1.5.1

frozenlist                1.5.0

fsspec                    2025.2.0

gast                      0.6.0

google-pasta              0.2.0

grpcio                    1.71.0

h11                       0.14.0

h5py                      3.13.0

httpcore                  1.0.7

httptools                 0.6.4

httpx                     0.28.1

hyperlink                 21.0.0

idna                      3.10

ifaddr                    0.2.0

ignite                    1.1.0

imagecodecs               2025.3.30

imageio                   2.35.1

importlib_metadata        8.5.0

incremental               24.7.2

ipykernel                 6.29.5

ipympl                    0.9.6

ipython                   8.27.0

ipywidgets                8.1.5

isoduration               20.11.0

itsdangerous              2.2.0

jedi                      0.19.1

Jinja2                    3.1.5

joblib                    1.4.2

json5                     0.12.0

jsonpointer               3.0.0

jsonrpc                   3.0.1

jsonrpc-base              2.2.0

jsonrpc-websocket         3.1.5

jsonschema                4.23.0

jsonschema-specifications 2024.10.1

jupyter                   1.1.1

jupyter_client            8.6.3

jupyter-console           6.6.3

jupyter_core              5.7.2

jupyter-events            0.12.0

jupyter-lsp               2.2.5

jupyter_server            2.16.0

jupyter_server_terminals  0.5.3

jupyterlab                4.4.2

jupyterlab_pygments       0.3.0

jupyterlab_server         2.27.3

jupyterlab_widgets        3.0.13

keras                     3.9.0

kiwisolver                1.4.7

lazy_loader               0.4

libclang                  18.1.1

llvmlite                  0.43.0

LMS-Conveyor              0.3.0

LMS-Fabric                0.9.3

lxml                      5.3.0

Markdown                  3.7

markdown-it-py            3.0.0

markdown2                 2.5.3

MarkupSafe                3.0.2

matplotlib                3.9.2

matplotlib-inline         0.1.7

mayavi                    4.8.2

mdurl                     0.1.2

mistune                   3.1.3

ml_dtypes                 0.5.1

monai                     1.4.0

mpld3                     0.5.10

mpmath                    1.3.0

msgpack                   1.1.0

msvc-runtime              14.36.32532

multidict                 6.1.0

namex                     0.0.8

natsort                   8.4.0

nbclient                  0.10.2

nbconvert                 7.16.6

nbformat                  5.10.4

ndindex                   1.9.1

nest-asyncio              1.6.0

networkx                  3.3

nicegui                   2.11.1

notebook                  7.4.2

notebook_shim             0.2.4

numba                     0.60.0

numexpr                   2.10.1

numpy                     1.26.1

opencv-python             4.10.0.84

opencv-python-headless    4.11.0.86

openpyxl                  3.1.5

opt_einsum                3.4.0

optree                    0.14.1

orjson                    3.10.15

overrides                 7.7.0

packaging                 25.0

pandas                    2.2.3

pandocfilters             1.5.1

paramiko                  3.5.0

parso                     0.8.4

pillow                    10.2.0

pip                       24.2

platformdirs              4.3.6

plotly                    5.24.1

prometheus_client         0.22.0

prompt_toolkit            3.0.47

propcache                 0.2.1

protobuf                  5.29.4

pscript                   0.7.7

psutil                    6.0.0

pure_eval                 0.2.3

py-cpuinfo                9.0.0

pyasn1                    0.6.1

pyasn1_modules            0.4.1

pycparser                 2.22

pydantic                  2.9.2

pydantic_core             2.23.4

pyface                    8.0.0

Pygments                  2.18.0

pylablib-lightweight      1.4.3

PyMuPDF                   1.24.10

PyMuPDFb                  1.24.10

PyNaCl                    1.5.0

PyOpenGL                  3.1.7

pyOpenSSL                 25.0.0

pyparsing                 3.1.4

pyperclip                 1.8.2

pypiwin32                 223

pyserial                  3.5

python-dateutil           2.9.0.post0

python-dotenv             1.0.1

python-engineio           4.11.2

python-json-logger        3.3.0

python-multipart          0.0.20

python-socketio           5.12.1

pythonnet                 3.0.4

pytorch-ignite            0.5.2

pytz                      2024.2

pyueye                    4.96.952

PyVISA                    1.14.1

pywin32                   306

pywinpty                  2.0.15

PyYAML                    6.0.2

pyzmq                     26.2.0

referencing               0.35.1

requests                  2.32.3

retrying                  1.3.4

rfc3339-validator         0.1.4

rfc3986-validator         0.1.1

rich                      13.9.4

roifile                   2025.5.10

rpds-py                   0.22.3

scikit-image              0.25.2

scikit-learn              1.5.2

scipy                     1.14.1

scour                     0.38.2

seaborn                   0.13.2

segment-anything          1.0

Send2Trash                1.8.3

service-identity          24.2.0

setuptools                68.2.2

simple-websocket          1.1.0

six                       1.16.0

sniffio                   1.3.1

soupsieve                 2.7

sqlite-bro                0.12.2

stack-data                0.6.3

starlette                 0.45.3

sympy                     1.14.0

tables                    3.10.1

tenacity                  9.0.0

tensorboard               2.19.0

tensorboard-data-server   0.7.2

tensorflow                2.19.0

tensorflow-hub            0.12.0

tensorflowjs              3.18.0

termcolor                 2.5.0

terminado                 0.18.1

tfjs-graph-converter      1.6.3

threadpoolctl             3.5.0

tifffile                  2024.9.20

tinycss2                  1.4.0

torch                     2.7.1

torchvision               0.22.1

tornado                   6.4.1

tqdm                      4.66.5

traitlets                 5.14.3

traits                    7.0.2

traitsui                  8.0.0

Twisted                   24.11.0

types-python-dateutil     2.9.0.20250516

typing_extensions         4.12.2

tzdata                    2024.2

umap                      0.1.1

uri-template              1.3.0

urllib3                   2.3.0

uvicorn                   0.34.0

vbuild                    0.8.2

vtk                       9.3.0

watchfiles                1.0.4

wcwidth                   0.2.13

webcolors                 24.11.1

webencodings              0.5.1

websocket-client          1.8.0

websockets                15.0

Werkzeug                  3.0.6

wheel                     0.40.0

widgetsnbextension        4.0.13

winpython                 7.0.20231126

wrapt                     1.17.2

wsproto                   1.2.0

wxPython                  4.2.1

yarl                      1.18.3

zipp                      3.21.0

zope.interface            7.2

[lfriedri]

Could be duplicate of jupyter-server/jupyverse#385

[lfriedri]

I could not find any documentation if the jupyter server should actually connect to the ipykernel in step (5) or if it should only offer a connection to it.

[lfriedri]

I am not sure if I actually need the jupyter server in this local-only-setup. I could also imagine VS code directly connecting to the ipykernel via ZMQ. But this is not supported, right?