Author: Jens Henrik Göbbert

Create your own Jupyter Kernel

Often the standard kernel do not provide all features you need for your work. This might be that certain modules are not loaded or packages are not installed.
With your own kernel you can overcome that problem easily and define your own environment, in which you work.

This notebook shows you how you can build your own kernel for a python environment.

---

Building your own Jupyter kernel is a three step process

1. Create/Pimp new virtual Python environment
   • venv
2. Create/Edit launch script for the Jupyter kernel
   • kernel.sh
3. Create/Edit Jupyter kernel configuration
   • kernel.json

Settings

• Set kernel name
  • must be lower case
  • change if you like

# INPUT NEEDED:
KERNEL_NAME=${USER}_kernel

export KERNEL_NAME=$(echo "${KERNEL_NAME}" | awk '{print tolower($0)}')
echo ${KERNEL_NAME} # double check

• List directories where JupyterLab will search for kernels

# JUPYTER SEARCH PATH (for kernels-directory)
echo "jupyter search paths for kernels-directories"
if [ -z $JUPYTER_PATH ]; then
  echo "$HOME/.local/share/jupyter"
else
  tr ':' '\n' <<< "$JUPYTER_PATH"
fi

Attention: Please choose 'private kernel' if you are unsure.
Using 'project kernel's need to be enabled for your project first by our Jupyter-JSC admins.

• Set kernel type
  • private kernel = "\${HOME}/.local/"
  • project kernel = "\${PROJECT}/.local/"
  • other kernel = "\<your-path>" (ensure it is part of $JUPYTER_PATH or your kernel will not be found by JuypterLab)

# INPUT NEEDED:
export KERNEL_TYPE=private # private, project or other
export KERNEL_SPECS_PREFIX=${HOME}/.local

###################
# project kernel
if [ "${KERNEL_TYPE}" == "project" ]; then
  export KERNEL_SPECS_PREFIX=${PROJECT}/.local
  echo "project kernel"
# private kernel
elif [ "${KERNEL_TYPE}" == "private" ]; then
  export KERNEL_SPECS_PREFIX=${HOME}/.local
  echo "private kernel"
else
  if [ ! -d "$KERNEL_SPECS_PREFIX" ]; then
    echo "ERROR: please create directory $KERNEL_SPECS_PREFIX"
  fi
  echo "other kernel"
fi
export KERNEL_SPECS_DIR=${KERNEL_SPECS_PREFIX}/share/jupyter/kernels

# check if kernel name is unique
if [ -d "${KERNEL_SPECS_DIR}/${KERNEL_NAME}" ]; then
  echo "ERROR: Kernel already exists in ${KERNEL_SPECS_DIR}/${KERNEL_NAME}"
  echo "       Rename kernel name or remove directory."
fi

echo ${KERNEL_SPECS_DIR}/${KERNEL_NAME} # double check

• Set directory for kernels virtual environment
  • change if you like

# INPUT NEEDED:
export KERNEL_VENVS_DIR=${PROJECT}/${USER}/jupyter/kernels

###################
mkdir -p ${KERNEL_VENVS_DIR}
if [ "${KERNEL_TYPE}" != "private" ] && [ "${KERNEL_TYPE}" != "other" ]; then
  echo "Please check the permissions and ensure your project partners have read/execute permissions:"
  namei -l ${KERNEL_VENVS_DIR}
fi

echo ${KERNEL_VENVS_DIR} # double check
ls -lt ${KERNEL_VENVS_DIR}

---

1. Create/Pimp new virtual Python environment

• 1.1 - Load basic Python module

module -q purge
module -q use $OTHERSTAGES        
module -q load Stages/2020    2> /dev/null # any stage can be used
module -q load GCCcore/.9.3.0 2> /dev/null
module -q load Python/3.8.5                # only Python is required
module list # double check

• 1.2 - Load extra modules you need for your kernel

# module load <module you need>

• 1.3 - Create and activate a virtual environment for the kernel
  and ensure python packages installed in the virtual environment are always prefered

if [ -d "${KERNEL_VENVS_DIR}/${KERNEL_NAME}" ]; then
  echo "ERROR: Directory for virtual environment already ${KERNEL_VENVS_DIR}/${KERNEL_NAME}"
  echo "       Rename kernel name or remove directory."
else
  python -m venv --system-site-packages ${KERNEL_VENVS_DIR}/${KERNEL_NAME}
  source ${KERNEL_VENVS_DIR}/${KERNEL_NAME}/bin/activate
  export PYTHONPATH=${VIRTUAL_ENV}/lib/python3.8/site-packages:${PYTHONPATH}
  echo ${VIRTUAL_ENV} # double check
fi

• 1.4 - Install Python libraries required for communication with Jupyter

which pip
if [ -z "${VIRTUAL_ENV}" ]; then
  echo "ERROR: Virtual environment not successfully initialized."
else
  pip install --ignore-installed ipykernel
  ls ${VIRTUAL_ENV}/lib/python3.8/site-packages/ # double check
fi

• 1.5 - Install whatever else you need in your Python virtual environment (using pip)

#pip install <python-package you need>

---

2. Create/Edit launch script for the Jupyter kernel

• 2.1 - Create launch script, which loads your Python virtual environment and starts the ipykernel process inside:

Attention: You MUST load the exactly the same modules as you did above for your virtual Python environment.

echo '#!/bin/bash'"

# Load basic Python module
module purge
module use "'$OTHERSTAGES'"
module load Stages/2020
module load GCCcore/.9.3.0
module load Python/3.8.5

# Load extra modules you need for your kernel (as you did in step 1.2)
#module load <module you need>
    
# Activate your Python virtual environment
source ${KERNEL_VENVS_DIR}/${KERNEL_NAME}/bin/activate
    
# Ensure python packages installed in the virtual environment are always prefered
export PYTHONPATH=${VIRTUAL_ENV}/lib/python3.8/site-packages:"'${PYTHONPATH}'"
    
exec python -m ipykernel "'$@' > ${VIRTUAL_ENV}/kernel.sh
chmod +x ${VIRTUAL_ENV}/kernel.sh

cat ${VIRTUAL_ENV}/kernel.sh # double check

---

3. Create/Edit Jupyter kernel configuration

• 3.1 - Create Jupyter kernel configuration directory and files

python -m ipykernel install --name=${KERNEL_NAME} --prefix ${VIRTUAL_ENV}
export VIRTUAL_ENV_KERNELS=${VIRTUAL_ENV}/share/jupyter/kernels

• 3.2 - Adjust kernel.json file

mv ${VIRTUAL_ENV_KERNELS}/${KERNEL_NAME}/kernel.json ${VIRTUAL_ENV_KERNELS}/${KERNEL_NAME}/kernel.json.orig

echo '{
  "argv": [
    "'${KERNEL_VENVS_DIR}/${KERNEL_NAME}/kernel.sh'",
    "-m",
    "ipykernel_launcher",
    "-f",
    "{connection_file}"
  ],
  "display_name": "'${KERNEL_NAME}'",
  "language": "python"
}' > ${VIRTUAL_ENV_KERNELS}/${KERNEL_NAME}/kernel.json

cat ${VIRTUAL_ENV_KERNELS}/${KERNEL_NAME}/kernel.json # double check

• 3.3 - Create link to kernel specs

mkdir -p ${KERNEL_SPECS_DIR}
cd ${KERNEL_SPECS_DIR}
ln -s ${VIRTUAL_ENV_KERNELS}/${KERNEL_NAME} .

echo -e "\n\nThe new kernel '${KERNEL_NAME}' was added to your kernels in '${KERNEL_SPECS_DIR}/'\n"
ls ${KERNEL_SPECS_DIR} # double check

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4. Cleanup

deactivate