"No CMAKE_CXX_COMPILER could be found" errror while deploying flask app on gcloud - cmake

Question

I have a flask application that I'm deploying on google cloud run. The app using a library 'face_recognition' that requires Cmake. I'm installing the CMake by running a command in DockerFile but getting an error. I don't know what it mean.
Here is my Dockerfile
# Use the official lightweight Python image.
# https://hub.docker.com/_/python
FROM python:3.9-slim
# Allow statements and log messages to immediately appear in the Knative logs
ENV PYTHONUNBUFFERED True
# Copy local code to the container image.
ENV APP_HOME /app
WORKDIR $APP_HOME
COPY . ./
# Install production dependencies.
RUN apt-get update && apt-get install -y cmake
RUN pip install --no-cache-dir -r requirements.txt
RUN pip install gunicorn
# Run the web service on container startup. Here we use the gunicorn
# webserver, with one worker process and 8 threads.
# For environments with multiple CPU cores, increase the number of workers
# to be equal to the cores available.
# Timeout is set to 0 to disable the timeouts of the workers to allow Cloud Run to handle instance scaling.
CMD exec gunicorn --bind :$PORT --workers 1 --threads 8 --timeout 0 main:app
Here is the error
CMake Error at CMakeLists.txt:14 (project):
No CMAKE_CXX_COMPILER could be found.
Tell CMake where to find the compiler by setting either the environment
variable "CXX" or the CMake cache entry CMAKE_CXX_COMPILER to the full path
to the compiler, or to the compiler name if it is in the PATH.
-- Configuring incomplete, errors occurred!
See also "/tmp/pip-install-2m1peq73/dlib_d6f82528b68745578021b2f234f89d7c/build/temp.linux-x86_64-3.9/CMakeFiles/CMakeOutput.log".
See also "/tmp/pip-install-2m1peq73/dlib_d6f82528b68745578021b2f234f89d7c/build/temp.linux-x86_64-3.9/CMakeFiles/CMakeError.log".
Traceback (most recent call last):
File "<string>", line 1, in <module>
File "/tmp/pip-install-2m1peq73/dlib_d6f82528b68745578021b2f234f89d7c/setup.py", line 222, in <module>
setup(
File "/usr/local/lib/python3.9/site-packages/setuptools/__init__.py", line 153, in setup
return distutils.core.setup(**attrs)
File "/usr/local/lib/python3.9/distutils/core.py", line 148, in setup
dist.run_commands()
File "/usr/local/lib/python3.9/distutils/dist.py", line 966, in run_commands
self.run_command(cmd)
File "/usr/local/lib/python3.9/distutils/dist.py", line 985, in run_command
cmd_obj.run()
File "/usr/local/lib/python3.9/site-packages/setuptools/command/install.py", line 61, in run
return orig.install.run(self)
File "/usr/local/lib/python3.9/distutils/command/install.py", line 546, in run
self.run_command('build')
File "/usr/local/lib/python3.9/distutils/cmd.py", line 313, in run_command
self.distribution.run_command(command)
File "/usr/local/lib/python3.9/distutils/dist.py", line 985, in run_command
cmd_obj.run()
File "/usr/local/lib/python3.9/distutils/command/build.py", line 135, in run
self.run_command(cmd_name)
File "/usr/local/lib/python3.9/distutils/cmd.py", line 313, in run_command
self.distribution.run_command(command)
File "/usr/local/lib/python3.9/distutils/dist.py", line 985, in run_command
cmd_obj.run()
File "/tmp/pip-install-2m1peq73/dlib_d6f82528b68745578021b2f234f89d7c/setup.py", line 134, in run
self.build_extension(ext)
File "/tmp/pip-install-2m1peq73/dlib_d6f82528b68745578021b2f234f89d7c/setup.py", line 171, in build_extension
subprocess.check_call(cmake_setup, cwd=build_folder)
File "/usr/local/lib/python3.9/subprocess.py", line 373, in check_call
raise CalledProcessError(retcode, cmd)

Answer 1

The container base python:3.9-slim is very stripped down. If your application requires CMake which often implies the gcc compiler as well,
you have at least two options:
Use a more feature rich base container such as debian:buster
Choose a container with those tools already configured.
Example Dockerfile to build a base container:
FROM debian:buster
RUN apt update && apt install -y gcc clang clang-tools cmake python3
You can then use that container as the base for future containers or modify the Dockerfile to include your application.
Docker debian:buster