A script to build an AWS Lambda overlay layer that installs `git` and all its dependencies.

make_git_layer.sh

#!/bin/bash
# Build an AWS Lambda zip file containing git and its dependencies

cat <<\EOF > tmp_build.sh
#!/bin/bash

# Comment this out if you want to see all the actions.
quiet=-q

# List of main executables from /usr/bin to copy into layer
main_execs=("git")

# List of libexec executables NOT to copy into layer
exclude_libexecs=("git-shell" "scalar")

echo "Installing packages"
# Install the git pacakge, as well file for testing the flie types and zip to package things up
yum install -y $quiet git file zip

echo "Copying executables"
# Create temporary bin and lib directories
mkdir -p /var/task/{bin,lib}

# Copy over main executables
for fname in ${main_execs[*]}; do
    cp /usr/bin/$fname /var/task/bin
done

# Copy over any libexec executables that are not symlinks and not in the exclude list
for fname in $(find /usr/libexec/git-core -type f -executable); do
    echo ${exclude_libexecs[*]} | grep -w -q $(basename $fname)
    if [ $? -ne 0 ]; then
        cp $fname /var/task/bin
    fi
done

echo "Copying libraries"
# Copy over all the library dependencies of the copied binaries
# (This could be more efficient, since it will copy a bunch of files multiple times)
for fname in /var/task/bin/*; do
    if [ $(file -b --mime-type $fname) == "application/x-sharedlib" ]; then
        ldd $fname | awk 'NF == 4 { system("cp " $3 " /var/task/lib/") }'
    fi     
done

echo "Fixing symlinks"
# Create symlinks for all the (non-excluded) linked executables
for fname in $(find /usr/libexec/git-core -type l); do
    source=$(basename $fname)
    target=$(basename $(readlink -f $fname))
    if [ ! -f bin/$source ]; then
        ln -s $target bin/$source
    fi
done

echo "Preparing zip file"
# Package temporary bin and lib into zip file.
zip --symlinks $quiet -r9 /build/git-layer.zip bin lib

echo "Done."


EOF

chmod +x tmp_build.sh

rm -f git-layer.zip
docker run --rm -it -v $(pwd):/build --entrypoint /build/tmp_build.sh amazon/aws-lambda-python
rm tmp_build.sh