Dockerfile

# FROM specifies a "base image" that should be used for the image we are about to create
FROM openjdk:8-jdk-alpine

# Allows us to specify a place on the local machine that container data should be persisted to
# So that it can be accessed even after the container shuts down (or while its running)
VOLUME /tmp

# Allows us to provide some value at image build time using the --build-arg flag
# For instance: docker build --build-arg profile=dev
ARG profile=local

# Creates and sets an environment variable that will be present in the resulting container
ENV PROFILE=${profile}

# Let's us include the created JAR file into the image, so it can be ran within the container
COPY target/*.jar prism.jar

# ADD vs COPY
# Effectively the same
# Technically, COPY is used when moving local files into the image
# ADD is used to grab external files and move them into the image

# Allows us to expose ports from the container to the host machine
# Used when we run the container
#                             host:container
# For instance: docker run -p 8080:5000
EXPOSE 5000

# Let's us specify a command to run during image building
RUN echo 'Hello from inside of the Docker image build process!'
RUN ls

# Let's us specify a command to be ran when the container starts
CMD echo 'Hello from inside of a Docker container!'

# Allows us to specify a primary command(s) that should be ran to initialize the container
# You cannot use ARGs in an ENTRYPOINT, only ENVs can be referenced
ENTRYPOINT [ "sh", "-c", "java -jar -Dspring.profiles.active=${PROFILE} prism.jar" ]