Creating more complex container image#

We might want to use files from outside the container * either by copying into the container images, * or by making them visible within a running container from their existing location on the host system.

Using scripts and files from outside the container#

cd to sum directory in the downloaded zip file.

(base) hell@Dell-Precision-T1600:~/Desktop/Docker/docker-intro/sum$ pwd
/home/hell/Desktop/Docker/docker-intro/sum

This directory has both Dockerfile and a python script called sum.py. We want to run the script using the container.

If we try this docker container run alice/alpine-python python3 sum.py We will get an error message like this python3: can't open file 'sum.py': [Errno 2] No such file or directory.

The problem here is the container has a seperate filesystem/OS. That is why containers can’t infect the host filesystem/OS. In order to use Python(inside the container) and our script (outside the container) we need to create a link between the directory on our computer and the container.

This link is called a mount and is just like mounting external drives to the computer. We need to have additional options to docker container run with --mount type=bind,scource=${PWD},target=/temp

Here, ${PWD} is the current working directory, you can substitute the source directory where the file or python script is on the host computer. The target is the mount point inside the container.

Types of mounts#

type can be bind, volume, tmfs. ## Final command to run external files docker container run --mount type=bind,source=${PWD},target=/temp USERNAME/CONTAINER_IMAGE_NAME COMMAND_TO_RUN

For example,

docker container run --mount type=bind,source=${PWD},target=/temp alice/alphine-python python3 /temp/sum.py

Note that if we create any files in the /temp directory while the container is running, these files will appear on our host filesystem in the original directory and will stay there even when the container stops.

  • docker container run: use Docker to run a container

  • --mount type=bind,source=${PWD},target=/temp: connect my current working directory (${PWD}) as a folder inside the container called /temp

  • alice/alpine-python: name of the container image to use to run the container

  • python3 /temp/sum.py: what commands to run in the container

The same container can be ran interactively with a mount point as follows

docker container run --mount type=bind,source=${PWD},target=/temp -it alice/alpine-python sh

Including your scripts and data within a container image#

Let’s assume that we’ve finished with our sum.py script and want to add it to the container image itself.

Add a newline into the Dockerfile to copy the file COPY sum.py. Then simply build the image as usual: docker image build -t alice/alpine-sum . ### The Importance of Command Order in a Dockerfile Docker builds things in layers. For example, if we put the COPY command before the RUN command, rebuilding needs to build the RUN layers again.

If the files are on a GITHUB repo#

Add this command in the end of the Dockerfile

RUN git clone https://github.com/alice/mycode

Similarly, the wget command can be used to download any file publicly available on the internet.

RUN wget ftp://ftp.ncbi.nlm.nih.gov/blast/executables/blast+/2.10.0/ncbi-blast-2.10.0+-x64-linux.tar.gz

More fancy Dockerfile options#

Make the sum.py script run automatically#

To achieve the goal of having a command that always runs when a container is run from the container image and can be passed the arguments given on the command line, use the keyword ENTRYPOINT in the Dockerfile.

FROM alpine

COPY sum.py /home
RUN apk add --update python3 py3-pip python3-dev

# Run the sum.py script as the default command and
# allow people to enter arguments for it
ENTRYPOINT ["python3", "/home/sum.py"]

# Give default arguments, in case none are supplied on
# the command-line
CMD ["10", "11"]

Build and test it#

$ docker image build -t alpine-sum:v2 .
# Most of the time you are interested in the sum of 10 and 11:
$ docker container run alpine-sum:v2
# Sometimes you have more challenging calculations to do:
$ docker container run alpine-sum:v2 12 13 14

Overriding the ENTRYPOINT#

Sometimes you don’t want to run the image’s ENTRYPOINT

docker container run -it alpine-sum:v2 /bin/sh

will yield

Please supply integer arguments

So, use --entrypoint to manually override the entrypoint.

docker container run -it --entrypoint /bin/sh alpine-sum:v2

Add the sum.py script to the PATH so you can run it directly#

Modify Dockerfile

FROM alpine

RUN apk add --update python3 py3-pip python3-dev

COPY sum.py /home
# set script permissions
RUN chmod +x /home/sum.py
# add /home folder to the PATH
ENV PATH /home:$PATH

$ docker image build -t alpine-sum:v3 .
$ docker container run alpine-sum:v3 sum.py 1 2 3 4