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Since I could not find a docker image on dockerhub that has maven 3.8.1, open jdk 11 and docker installed, I tried to create one with a Dockerfile. I am new to this hence facing issues. Below is how my Dockerfile looks like

FROM maven:3.8.1-adoptopenjdk-11
RUN apt update -y
RUN apt install -y curl
RUN curl https://get.docker.com/builds/Linux/x86_64/docker-latest.tgz | tar xvz -C /tmp/ && mv /tmp/docker/docker /usr/bin/docker
RUN docker ps

When I execute docker build -t demo . I get the below error logs

docker/docker-containerd
 38 27.1M   38 10.3M    0     0  18.5M      0  0:00:01 --:--:--  0:00:01 18.5Mdocker/docker-proxy
docker/docker-containerd-ctr
docker/dockerd
docker/docker-runc
100 27.1M  100 27.1M    0     0  19.7M      0  0:00:01  0:00:01 --:--:-- 19.7M
Removing intermediate container f4cd71aa05d2
 ---> 7b0055db2e58
Step 5/5 : RUN docker ps
 ---> Running in 83919a2985bf
Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?

My goal is to create a Dockerfile that could be used in a jenkins pipeline to build a maven spring boot project (mvn spring-boot:build-image). Could someone guide me on the Dockerfile?

Thanks.

David Maze
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Andy Dufresne
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  • When running docker-in-docker, you map the host docker socket into the container, so it can access it. But that only works when running the container. I don't think there's any way to access it during build time like you're trying to do. – Hans Kilian Dec 01 '21 at 13:49
  • I could do it at runtime too when jenkins would execute my pipeline script. Basically I need to provide jenkins a docker image that has maven, jdk 11 and docker installed. If I were do run docker inside docker at runtime, could you show me how my Dockerfile should look like and how should the docker run command be? – Andy Dufresne Dec 01 '21 at 13:52

1 Answers1

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Here's a Dockerfile that installs the docker-ce-cli package on the Maven image you use as your base. You don't need docker-ce or containerd. The commands to install are taken from the docker website.

FROM maven:3.8.1-adoptopenjdk-11
RUN apt update && \
    apt install -y ca-certificates curl gnupg lsb-release && \
    curl -fsSL https://download.docker.com/linux/ubuntu/gpg | gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg && \
    echo "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable" | tee /etc/apt/sources.list.d/docker.list > /dev/null && \
    apt update && \
    apt install -y docker-ce-cli

Then, when you run it, you map /var/run/docker.sock on the host to /var/run/docker.sock in the container and now the container can talk to the docker daemon on the host.

Here's how I ran it on Windows. The 2 slashes at the front of the mapping is due to how Windows and WSL2 work. On a Linux host, you'd do -v /var/run/docker.sock:/var/run/docker.sock.

C:\>docker build -t dind .    
C:\>docker run --rm -it --entrypoint /bin/bash -v "//var/run/docker.sock:/var/run/docker.sock" dind
root@d63b0fedd3e4:/# mvn --version
Apache Maven 3.8.1 (05c21c65bdfed0f71a2f2ada8b84da59348c4c5d)
Maven home: /usr/share/maven
Java version: 11.0.11, vendor: AdoptOpenJDK, runtime: /opt/java/openjdk
Default locale: en_US, platform encoding: UTF-8
OS name: "linux", version: "5.4.72-microsoft-standard-wsl2", arch: "amd64", family: "unix"
root@d63b0fedd3e4:/# java --version
openjdk 11.0.11 2021-04-20
OpenJDK Runtime Environment AdoptOpenJDK-11.0.11+9 (build 11.0.11+9)
OpenJDK 64-Bit Server VM AdoptOpenJDK-11.0.11+9 (build 11.0.11+9, mixed mode)
root@d63b0fedd3e4:/# docker --version
Docker version 20.10.11, build dea9396
root@d63b0fedd3e4:/# docker ps
CONTAINER ID   IMAGE     COMMAND       CREATED          STATUS          PORTS     NAMES
d63b0fedd3e4   dind      "/bin/bash"   19 seconds ago   Up 18 seconds             nifty_zhukovsky
root@d63b0fedd3e4:/#

I hope that gets you started and you can add the installation of any other packages you need.

Hans Kilian
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  • Do we get the same output if use this [image](https://hub.docker.com/layers/docker/library/docker/dind/images/sha256-6b91496cd8473f8f0412be846318dcf073a41e5c02fea27a75a657376c55e83b?context=explore)? The next question is how do I merge the two images - this one and maven:3.8.1-adoptopenjdk-11. That's the real part I am struggling with. – Andy Dufresne Dec 01 '21 at 14:32
  • Yes, you can use the `dind` image from docker hub as well. As for merging the images, I don't think there's any way around making the image yourself. You'll have to figure out which image to base your own on and then create a Dockerfile to install the extra packages to get an image with all the things you need. – Hans Kilian Dec 01 '21 at 14:35
  • That's what I tried to do (refer to the original Dockerfile in my post) and failed – Andy Dufresne Dec 01 '21 at 14:36
  • If you take the Dockerfile I've made and replace `FROM ubuntu` with `FROM maven:3.8.1-adoptopenjdk-11` you should get an image with Maven and Docker. Do you need more than that? (I edited my answer to use the Maven image as the base image) – Hans Kilian Dec 01 '21 at 14:39
  • Works as expected. Would this docker image or the run command have any security concerns that I need to be aware off (asking since its running docker inside docker)? – Andy Dufresne Dec 02 '21 at 08:29
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    Since it can talk to the docker daemon and start new containers, whatever runs in the container effectively has root access on the host computer. See this for more information: https://docs.docker.com/engine/security/#docker-daemon-attack-surface – Hans Kilian Dec 02 '21 at 08:40