How to locate openjdk in Docker container? - docker

Question

I tried to run the pyspark application.For this first I installed pyspark from pip then pulled openjdk:8 to set the JAVA_HOME variable
Dockerfile :
FROM python:3
ADD my_script.py /
COPY requirements.txt ./
ENV JAVA_HOME /usr/lib/jvm/java-8-openjdk-amd64/
RUN pip install --no-cache-dir -r requirements.txt
CMD [ "python", "./my_script.py" ]
my_script.py :
from pyspark import SparkContext
from pyspark import SparkConf
#spark conf
conf1 = SparkConf()
conf1.setMaster("local[*]")
conf1.setAppName('hamza')
print(conf1)
sc = SparkContext(conf = conf1)
from pyspark.sql import SQLContext
sqlContext = SQLContext(sc)
print(sqlContext)
Requirements.txt :
pyspark
numpy
Getting this error :
C:\Users\hrafiq\Desktop\sample>docker run -it --rm --name data2 my-python-app
<pyspark.conf.SparkConf object at 0x7f4bd933ba58>
/usr/local/lib/python3.7/site-packages/pyspark/bin/spark-class: line 71:
/usr/lib/jvm/java-8-openjdk-amd64//bin/java: No such file or directory
Traceback (most recent call last):
File "./my_script.py", line 14, in <module>
sc = SparkContext(conf = conf1)
File "/usr/local/lib/python3.7/site-packages/pyspark/context.py", line 115, in __init__
SparkContext._ensure_initialized(self, gateway=gateway, conf=conf)
File "/usr/local/lib/python3.7/site-packages/pyspark/context.py", line 298, in _ensure_initialized
SparkContext._gateway = gateway or launch_gateway(conf)
File "/usr/local/lib/python3.7/site-packages/pyspark/java_gateway.py", line 94, in launch_gateway
raise Exception("Java gateway process exited before sending its port number")
Exception: Java gateway process exited before sending its port number
So the question is If is not finding the java file then how will I find the that file? I know it is stored in some virtual hard disk which we dont have any access.
Any help would be appreciated
Thanks

Answer 1

Setting the JAVA_HOME env var is not enough. You need to actually install openjdk inside your docker image.
Your base image (python:3) is itself based on a Debian Stretch image. So you can use apt-get install to fetch the JDK :
FROM python:3
RUN apt-get update && \
apt-get install -y openjdk-8-jdk-headless && \
rm -rf /var/lib/apt/lists/*
ENV JAVA_HOME /usr/lib/jvm/java-8-openjdk-amd64/
COPY requirements.txt ./
RUN pip install --no-cache-dir -r requirements.txt
COPY my_script.py ./
CMD [ "python", "./my_script.py" ]
(In the above I have optimized the layers ordering so that you won't need to re-build the pip install layer when only your script changes)