OTHER Dockerfile Directives
- ENTRYPOINT: This directive is used to set the executable to started while creating container. For understanding refer Exploring CMD section below.
- ENV
- ARG
- WORKDIR
- USER
Exploring CMD
- CMD will be executed when we are creating a container.
- Whatever is written in CMD can be overriten while creating the container by passing the commands after image name.
- Consider the following dockerfile
FROM alpine:3.10.4
LABEL author="khaja"
CMD ["echo", "hello"]
- Build the image and run the container
- Now consider the following Dockerfile
FROM alpine:3.10.4
LABEL author="khaja"
ENTRYPOINT [ "echo" ]
CMD ["hello"]
Exploring ARG
- Consider the following Dockerfile
FROM openjdk:11
LABEL author="khaja"
LABEL project="qtdevops"
ADD https://referenceapplicationskhaja.s3.us-west-2.amazonaws.com/spring-petclinic-2.4.2.jar /spring-petclinic-2.4.2.jar
EXPOSE 8080
CMD [ "java", "-jar", "/spring-petclinic-2.4.2.jar" ]
- In the above dockerfile while building the image the source from which we copy the file is used only while building the image and this might change in the future
- Refer Here for the changes done
- Now build the image
- Now lets experiment
- Refer Here and Now lets build the image
- Lets change the build location while building the image
- ARGS can be passed while building the image whereas ENV can be passed while creating the container
- Note: If you need to change a varible during image build time as well as during CONTAINER CREATION Refer Here
- One possible use case is to download the file to any location
FROM openjdk:11
LABEL author="khaja"
LABEL project="qtdevops"
ARG SOURCE_JAR_LOCATION=https://referenceapplicationskhaja.s3.us-west-2.amazonaws.com/spring-petclinic-2.4.2.jar
ARG DESTINATION="/spring-petclinic-2.4.2.jar"
ADD ${SOURCE_JAR_LOCATION} ${DESTINATION}
ENV DESTINATION=${DESTINATION}
RUN echo "ENV: ${TESTING}, ARG ${SOURCE_JAR_LOCATION}"
EXPOSE 8080
CMD [ "java", "-jar", "/spring-petclinic-2.4.2.jar" ]
- Exercise Try using DESTINATION VARIABLE in CMD
