Lambda function to solve sudoku puzzles 🔢

The solver in lambda_function.py combines a constraint-model-based algorithm with backtracking

Run locally

To run on your local machine, first prepare the environment

# build a virutal environment
python3.8 -m venv v-env
. ./v-env/bin/activate
pip install -r requirements.txt
pip install numpy

Then run one of the sudoku grid available in the data/ folder

python lambda_function_local.py data/sudoku_04.txt

Build the deployment package

A lot of issues have been reported when using numpy or pandas libraries in a lambda function. To avoid running into conflicts and relying on which OS it is build, let's use docker.

1. Download the amazonlinux image from dockerhub and jump inside the container

docker pull amazonlinux
docker run -ti -v $PWD:/app amazonlinux

2. Install the relevant python (3.8) and pip version

yum -y install wget zip unzip tar gzip gcc openssl-devel bzip2-devel libffi-devel make
wget https://www.python.org/ftp/python/3.8.2/Python-3.8.2.tgz
tar xzf Python-3.8.2.tgz
cd Python-3.8.2
./configure --enable-optimizations
make altinstall
rm Python-3.8.2.tgz

curl -O https://bootstrap.pypa.io/get-pip.py
python3.8 get-pip.py --user

3. Build the deployment package

# Move where the repo has been mounted
cd ../app

# Create and activate a virtual environment
python3.8 -m venv v-env
. ./v-env/bin/activate

# Install the libraries (make sure there is no numpy here)
pip3.8 install -r requirements.txt

# Manually add Numpy to the site-packages
cd v-env/lib/python3.8/site-packages
wget https://files.pythonhosted.org/packages/cf/5d/e8198f11dd73a91f7bde15ca88a2b78913fa2b416ae2dc2a6aeafcf4c63d/numpy-1.18.4-cp38-cp38-manylinux1_x86_64.whl
unzip numpy-1.18.4-cp38-cp38-manylinux1_x86_64.whl
rm numpy-1.18.4-cp38-cp38-manylinux1_x86_64.whl

# Exit the virtual env
deactivate

# Package the function
zip -r9 ${OLDPWD}/function.zip .
cd ${OLDPWD}
zip -g -r function.zip lambda_function.py

4. Finally, copy your package function.zip from the container into your local machine

In new terminal tab without closing the tab running the container

# Check the id of you running container
docker ps
# Copy the package to local
docker cp <CONTAINER ID>:/app/function.zip .

Upload the package to aws

If function.zip is smaller than 50M, the easiest would be to use the aws console, create a new Lambda function with a python 3.7 runtime and upload the zip file. If the file is larger then place it in a S3 bucket.

• To check the size of the file

du -hs function.zip

• To create a function with the CLI

aws lambda create-function --function-name SolveSudoku \
--zip-file fileb://function.zip --handler lambda_function.lambda_handler --runtime python3.7 \
--timeout 60 \
--role arn:aws:iam::XXXXXXXXXX:role/lambda-s3-role

• To update the function with the CLI

aws lambda update-function-code \
    --function-name  SolveSudoku \
    --zip-file fileb://function.zip