dockerfile : npm not found at entrypoint? - node.js

Question

I have this dockerfile :
ARG DEBIAN_FRONTEND=noninteractive
FROM ubuntu:latest
WORKDIR .
COPY . /service/api/
RUN apt-get update -y && apt-get install -y openssl python3 curl
ENV NODE_VERSION 16.19.1
# install nvm
RUN cd / && curl https://raw.githubusercontent.com/creationix/nvm/master/install.sh | bash && cd / && \
export NVM_DIR="$HOME/.nvm" && [ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh" && nvm install $NODE_VERSION && \
cd /service/api/ && rm -rf node_modules && npm install
ENV NODE_PATH $NVM_DIR/v$NODE_VERSION/lib/node_modules
ENV PATH $NVM_DIR/versions/node/v$NODE_VERSION/bin:$PATH
ADD start.sh /start.sh
#ENTRYPOINT ["tail", "-f", "/dev/null"]
CMD cd /service/api/ && npm start
The image compiles correctly but it can't start because 'npm not found'.
When I uncomment the other debug entrypoint above to exec in the container, I see that npm -v and node -v are available in it.
Why aren't they available in my entrypoint ?

Answer 1

The problem is that RUN ... export NVM_DIR="$HOME/.nvm" does not allow you to use $NVM_DIR later in the Dockerfile to benefit from Docker variables substitutions. Only variables defined by a line starting with ENV can be used later (except when using the variable in a line starting with RUN, but this variable replacement is not implemented by Docker but by a shell). Therefore, your Dockerfile line ENV NODE_PATH $NVM_DIR/v$NODE_VERSION/lib/node_modules does not resolve $NVM_DIR to the correct path ($NVM_DIR is simply replaced by an empty string, at this step).
Simply add ENV NVM_DIR /root/.nvm just before ENV NODE_PATH $NVM_DIR/v$NODE_VERSION/lib/node_modules and this will correct your Dockerfile.
The correct Dockerfile should be:
ARG DEBIAN_FRONTEND=noninteractive
FROM ubuntu:latest
WORKDIR .
COPY . /service/api/
RUN apt-get update -y && apt-get install -y openssl python3 curl
ENV NODE_VERSION 16.19.1
# install nvm
RUN cd / && curl https://raw.githubusercontent.com/creationix/nvm/master/install.sh | bash && cd / && \
export NVM_DIR="$HOME/.nvm" && [ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh" && nvm install $NODE_VERSION && \
cd /service/api/ && rm -rf node_modules && npm install
ENV NVM_DIR /root/.nvm
ENV NODE_PATH $NVM_DIR/v$NODE_VERSION/lib/node_modules
ENV PATH $NVM_DIR/versions/node/v$NODE_VERSION/bin:$PATH
ADD start.sh /start.sh
#ENTRYPOINT ["tail", "-f", "/dev/null"]
CMD cd /service/api/ && npm start