How to execute npm start within dockerfile CMD script

Question

The following Dockerfile runs a simple script which is supposed to start a React application and a python application:

# syntax=docker/dockerfile:1

FROM nikolaik/python-nodejs

WORKDIR /app

COPY requirements.txt requirements.txt
RUN pip3 install -r requirements.txt

COPY RPDC-front-end/package.json RPDC-front-end/package.json
RUN cd RPDC-front-end && npm install

COPY . .

EXPOSE 1234

RUN chmod u+r+x wrapper-script.sh

CMD ./wrapper-script.sh

The ./wrapper-script.sh file is as follows:

#!/bin/sh

python3 -m launcher.py
cd RPDC-front-end && npm start

I can see that both the python and node packages install within their appropriate locations, but only the python application starts. The npm start command from the wrapper-script does not seem to work. However, if I open up the terminal of the running container and manually run npm start within the RDPC-front-end directory (where all of the node packages and associated code are), the application builds and is accessible via port 1234. How can I fix my script/dockerfile so that the npm start command works?

Answer 1

Although you should NOT use the same container to run more than one service, the issue here is that the call to

python3 -m launcher.py

is (I think) blocking, which means that the shell will not continue to execute commands until this one exits.

Instead try to put a & after the python command to run it in background:

python3 -m launcher.py &

Answer 2

Try changing your Dockerfile to this:

# syntax=docker/dockerfile:1

FROM nikolaik/python-nodejs

WORKDIR /app

COPY requirements.txt requirements.txt
RUN pip3 install -r requirements.txt

COPY RPDC-front-end/package.json RPDC-front-end/package.json
RUN cd RPDC-front-end && npm install

COPY . .

EXPOSE 1234

RUN chmod u+r+x wrapper-script.sh

CMD ["python3", "-m launcher.py"]

RUN cd RPDC-front-end && npm start

If you want to keep your script file, you can check why 'npm start' is failing, just change the script to this:

#!/bin/sh

python3 -m launcher.py
cd RPDC-front-end ; npm start 2> errorLog.txt

The error message will be stored in errorLog.txt if the command fails.