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Docker - Building Container Images

Lab assignment for creating a container using containerd and docker.

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By Sakharam Shinde
7 min read
Docker - Building Container Images

Prerequisites

  • Docker

Assignment

  • Lets build a container using the github repository created for running a Matrix screensaver.
  • Languages: C

  1. Pull a base docker image ‘alpine’ - Ultrasmall and minimal image based on alpine linux (size: ~8MB)

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     docker pull alpine

  2. Verify if the images exists on your host

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     docker images

  3. Create a Dockerfile using the apline images

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     cat <<EOF> ./Dockerfile
 FROM alpine

 LABEL org.opencontainers.image.authors="Sakharam Shinde"
 EOF

  4. Build a docker image using the Dockerfile (Same as base image with just additional label)

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     docker build -t sakharamshinde/cmatrix .

  5. Verify if the new images is created with the defined tag.

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     docker images

  6. Create a container using the new image and ssh into the container

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     docker run --rm -it sakharamshinde/cmatrix sh

  7. Once we are into the shell of the container, execute below steps to get the cmatrix running inside the container.

    • Verify the Hostname
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     hostname
    • Clone the Repository, this will fail
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     # 
 git clone https://github.com/abishekvashok/cmatrix.git

  8. Since git is not installed in the base image, we will install the git tool.

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     apk update

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     apk add git
    • Clone the repo
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     git clone https://github.com/abishekvashok/cmatrix.git
    • Switch to the repo dir and check the contents
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     cd cmatrix

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     ls -l

  9. Similarly, install the required packages required to build the cmatrix screensave

    • Prepare compilation, will fail, missing autoconf
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     autoreconf -i
    • Install autoconf
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     apk add autoconf
    • Prepare compilation, will fail, missing automake
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     autoreconf -i
    • Install automake
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     apk add automake
    • Prepare compilation, will succeed, confirm with echo $?
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     autoreconf -i
    • Verify it the install was successful
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     echo $?
    • Prepare configure, will fail, missing compiler
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     ./configure LDFLAGS="-static"
    • Install compiler
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     apk add alpine-sdk
    • Prepare configure, will fail, missing dependencies
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     ./configure LDFLAGS="-static"
    • Install dependencies and create missing directories
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     apk add ncurses-dev ncurses-static

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     mkdir -p /usr/lib/kbd/consolefonts /usr/share/consolefonts
    • Prepare configure, will succeed
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     ./configure LDFLAGS="-static"
    • Compile and view result
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     make
    • Check the created binary
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     ls -l ./cmatrix
    • Run cmatrix
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     ./cmatrix

  10. Build a docker image for the cmatrix app using all the command used above.

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    cat <<EOF> ./Dockerfile
FROM alpine

LABEL org.opencontainers.image.authors="Sakharam Shinde"

RUN apk update

RUN apk add git 

RUN git clone https://github.com/abishekvashok/cmatrix.git .

RUN cd cmatrix

RUN apk add autoconf

RUN apk add automake

RUN autoreconf -i

RUN apk add alpine-sdk

RUN apk add ncurses-dev ncurses-static

RUN mkdir -p /usr/lib/kbd/consolefonts /usr/share/consolefonts

RUN ./configure LDFLAGS="-static"

RUN make

CMD ["./cmatrix"]

EOF
    • Build a new image with the updated Dockerfile
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    docker build -t sakharamshinde/cmatrix .
    • Run the new image, this will fail
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    docker run --rm -it sakharamshinde/cmatrix
    • Specify the working directory for the Dockerfile
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    cat <<EOF> ./Dockerfile
FROM alpine

LABEL org.opencontainers.image.authors="Sakharam Shinde"

WORKDIR /cmatrix

RUN apk update

RUN apk add git 

RUN git clone https://github.com/abishekvashok/cmatrix.git .

RUN apk add autoconf

RUN apk add automake

RUN autoreconf -i

RUN apk add alpine-sdk

RUN apk add ncurses-dev ncurses-static

RUN mkdir -p /usr/lib/kbd/consolefonts /usr/share/consolefonts

RUN ./configure LDFLAGS="-static"

RUN make

CMD ["./cmatrix"]

EOF
    • Build a new image with the updated Dockerfile
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    docker build -t sakharamshinde/cmatrix .
    • Run the new image, this will succeed
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    docker run --rm -it sakharamshinde/cmatrix

  11. Check the size of the new image and inspect the layers

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    docker images

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    docker history sakharamshinde/cmatrix

  12. To reduce the number of layers, we will combine common commands into one

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    cat <<EOF> ./Dockerfile
FROM alpine

LABEL org.opencontainers.image.authors="Sakharam Shinde"

WORKDIR /cmatrix

RUN apk update --no-cache && \
    apk add git autoconf automake alpine-sdk ncurses-dev ncurses-static
        
RUN git clone https://github.com/abishekvashok/cmatrix.git .
    
RUN autoreconf -i
    
RUN mkdir -p /usr/lib/kbd/consolefonts /usr/share/consolefonts
    
RUN ./configure LDFLAGS="-static"

RUN make
    
CMD ["./cmatrix"]
    
EOF
    • Build the image
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    docker build -t sakharamshinde/cmatrix .
    • Run the new image
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    docker run --rm -it sakharamshinde/cmatrix

  13. Check the size of the image and inspect the layers

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    docker images

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    docker history sakharamshinde/cmatrix

  14. To reduce the size further, we can combine all the RUN commands

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    cat <<EOF> ./Dockerfile
FROM alpine

LABEL org.opencontainers.image.authors="Sakharam Shinde"

WORKDIR /cmatrix

RUN apk update --no-cache && \
apk add git autoconf automake alpine-sdk ncurses-dev ncurses-static && \
git clone https://github.com/abishekvashok/cmatrix.git . && \
autoreconf -i && \
mkdir -p /usr/lib/kbd/consolefonts /usr/share/consolefonts && \
./configure LDFLAGS="-static" && \
make
    
CMD ["./cmatrix"]
    
EOF
    • Build the image
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    docker build -t sakharamshinde/cmatrix .
    • Run the new image
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    docker run --rm -it sakharamshinde/cmatrix

  15. Check the size of the image and inspect the layers

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    docker images

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    docker history sakharamshinde/cmatrix

  16. Build the image using multi-stage docker build

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    cat <<EOF> ./Dockerfile
# Build Container Image
FROM alpine AS cmatrixbuilder 

WORKDIR /cmatrix

RUN apk update --no-cache && \
    apk add git autoconf automake alpine-sdk ncurses-dev ncurses-static && \
    git clone https://github.com/abishekvashok/cmatrix.git . && \
    autoreconf -i && \
    mkdir -p /usr/lib/kbd/consolefonts /usr/share/consolefonts && \
    ./configure LDFLAGS="-static" && \
    make

# cmatrix Container Image
FROM alpine

LABEL org.opencontainers.image.authors="Sakharam Shinde" \

RUN apk update --no-cache && \
    apk add ncurses-terminfo-base

COPY --from=cmatrixbuilder /cmatrix/cmatrix /cmatrix

CMD ["./cmatrix"]

EOF
    • Build the image
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    docker build -t sakharamshinde/cmatrixms .
    • Run the new image
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    docker run --rm -it sakharamshinde/cmatrixms

  17. Check the user running the container

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    docker run --rm -it sakharamshinde/cmatrixms whoami

  18. Run the container as a user instead of root

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    cat <<EOF> ./Dockerfile
# Build Container Image
FROM alpine AS cmatrixbuilder 

WORKDIR /cmatrix

RUN apk update --no-cache && \
    apk add git autoconf automake alpine-sdk ncurses-dev ncurses-static && \
    git clone https://github.com/abishekvashok/cmatrix.git . && \
    autoreconf -i && \
    mkdir -p /usr/lib/kbd/consolefonts /usr/share/consolefonts && \
    ./configure LDFLAGS="-static" && \
    make
    
# cmatrix Container Image
FROM alpine
    
LABEL org.opencontainers.image.authors="Sakharam Shinde" \

RUN apk update --no-cache && \
    apk add ncurses-terminfo-base && \
    adduser -g "Sakharam" -s /usr/sbin/nologin -D -H sakharam

COPY --from=cmatrixbuilder /cmatrix/cmatrix /cmatrix

USER sakharam
CMD ["./cmatrix"]
EOF
    • Build the image
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    docker build -t sakharamshinde/cmatrixms .
    • Run the new image
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    docker run --rm -it sakharamshinde/cmatrixms

  19. Run the container with entrpoint and commands

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    cat <<EOF> ./Dockerfile
# Build Container Image
FROM alpine AS cmatrixbuilder 

WORKDIR /cmatrix

RUN apk update --no-cache && \
    apk add git autoconf automake alpine-sdk ncurses-dev ncurses-static && \
    git clone https://github.com/abishekvashok/cmatrix.git . && \
    autoreconf -i && \
    mkdir -p /usr/lib/kbd/consolefonts /usr/share/consolefonts && \
    ./configure LDFLAGS="-static" && \
    make
    
# cmatrix Container Image
FROM alpine
    
LABEL org.opencontainers.image.authors="Sakharam Shinde" \

RUN apk update --no-cache && \
    apk add ncurses-terminfo-base && \
    adduser -g "Sakharam" -s /usr/sbin/nologin -D -H sakharam

COPY --from=cmatrixbuilder /cmatrix/cmatrix /cmatrix

USER sakharam
ENTRYPOINT ["./cmatrix"]
CMD ["-b"]

EOF
  • Build the image
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```sh
docker build -t sakharamshinde/cmatrixms .
```

- Run the new image

```sh
docker run --rm -it sakharamshinde/cmatrixms --help
```
devops, orchestration, docker
Assignments
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