Google App Engine: JAVA command not recognized by Python in Flex environment with Docker (`java` command is not found from this Python process)

Question

I deployed a Python project on Google App Engine. As the project has a dependency on Java, I used a Docker container configuring two environments: Python + Java.

However, when I make a call to my Python service in GAE it's getting " java command is not found from this Python process. Please ensure Java is installed and PATH is set for java " error .

During the build process of the Docker file I am able to access Java after installing it. But during API execution it is not recognized by Python.

The "app.yaml" file used:

runtime: custom
env: flex
entrypoint: gunicorn -w 4 -k uvicorn.workers.UvicornWorker src.main:app

Below are the the Docker file used in Deploy:

### 1. Get Linux
FROM alpine:3.7
    
# Default to UTF-8 file.encoding
ENV LANG C.UTF-8

### 2. Get Java via the package manager
RUN apk update \
&& apk upgrade \
&& apk add --no-cache bash \
&& apk add --no-cache --virtual=build-dependencies unzip \
&& apk add --no-cache curl \
&& apk add --no-cache openjdk8-jre

#### OPTIONAL : 4. SET JAVA_HOME environment variable, uncomment the line below if you need it
ENV JAVA_HOME="/usr/lib/jvm/java-1.8-openjdk"
RUN export JAVA_HOME
ENV PATH $PATH:$JAVA_HOME/bin
RUN export PATH
RUN find / -name "java"
RUN java -version  

FROM python:3.7
EXPOSE 8080

ENV APP_HOME /src
WORKDIR /src

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

COPY . /src
CMD ["uvicorn", "src.main:app", "--host", "0.0.0.0", "--port", "8080"]

Here is a printout of the RUN java -version command during the deploy process: RUN java -version command

Does anyone know why the error is happening even with Python and Java running on the same service on App Engine? Are there any additional settings missing?

Answer 1

You are using two FROM in a Dockerfile, so you're effectively doing a multi-stage Docker build, but you are doing it wrong. A multi-stage build should be something like this:

### 1. Get Linux
FROM alpine:3.7 as build
# here you install with apk and build your Java program

FROM python:3.7
EXPOSE 8080 
...
# here you copy what you need from the previous Docker build, though 
# since it was Java, which is not installed here anymore because it is
# a python image, you need to consider if you really need a multi-stage 
# build 
COPY --from=builder /src /src

Otherwise, just remove the second FROM python:3.7 and install it with apk.