How should I use environment variables at the Entrypoint in Docker?

Question

ENV ADDRESS=http://peer1:8761/eureka/,http://peer2:8762/eureka/
ENTRYPOINT ["java","-Djava.security.egd=file:/dev/./urandom", "-jar","/app.jar", "--eureka.client.serviceUrl.defaultZone=$ADDRESS"]

I want to specify the eureka address to the entrypoint via environment variables.But it still $ADDRESS when i use docker run,and i use ENTRYPOINT java -jar xxxx ，it can be replaced correctly,but when i use ENTRYPOINT like ENTRYPOINT java -jar xxx.jar ,and i use docker run image_name --spring.profiles.active=peer1 ,ending parameters active=peer1 will not take effect,What should I do to use environment variables and parameters in Entrypoint

Answer 1

I just tried resolving PATH in dockerfile and it worked for one scenario (I used CMD though) not sure if that helps. If this did not work let me know with more details.

There are two forms to specify command (Exec form and Shell form), and two ways to specify the default command(ENTRYPOINT and CMD) in a dockerfile.

Exec form:

FROM ubuntu
MAINTAINER xyz<xyz.gmail.com>
ENTRYPOINT ["ping"]

The command specified (ping) will run as PID 1. That is the reason why if we press CTRL + C (SIGTERM) is passed to PID1 process and container is shutdown.

Shell form:

FROM ubuntu
MAINTAINER xyz<xyz.gmail.com>
CMD echo $PATH

PATH got resolved to the shell environment PATH when run.(output verified).

shell form specifiies command tokens separated by spaces. shell form executes command by calling /bin/sh -c (this means PID 1 is actually the shell and the command specified in docker file is just another process)(pressing CTRL + C will not kill container)

Advantage of using shell form is since you are executing with /bin/sh -c we can resolve environment variables in command (in above example we are using PATH).

Hope this helps