docker ARG and ENV

1. ARG is only available during build
2. ENV is available can be available during build as well as after the build

FROM httpd
ARG arg1
ENV env1=evalue1
ENV env2=${arg1}
ENV env3=evalue3

docker build --build-arg arg1=atest -t httpd-test .

docker run -d --env-file=env_file  httpd-test