Dylan North

Dylan North


How to build a Docker container for beginners

Docker is a software platform that allows you to quickly build, test, and deploy applications. Docker packs software into standardized units called containers that contain everything the software needs to run, including libraries, system tools, code, and runtime…

It has been a few years now from the container explosion and the ecosystem is starting to settle down. After all the big names in industry jumped in the containerization wagon, very often proposing their own solution, it seems like Docker based platforms are finally here to stay.

After Docker became the de facto standard, many things have evolved, most often under the hood. The Open Container Iniciative (OCI) was created with the objective of standardizing run times and image formats and Docker changed its internal plumbing to accommodate, such as implementing runC, and containerd-shim.

Now, after years of Docker freezing its user facing APIs we are starting to see movement again on this front, and many of the common practices we are used to seeing when building and running containers might have better alternatives. Other things have just been deprecated or fallen out of favor.

Buildkit is here

Now Dockerfiles can be built with the Buildkit backend. This backend is smarter than the classic one, and is able to speed up the build process by achieving smarter caching, parallelizing build steps and also it accepting new Dockerfile options. To quote the official documentation

Starting with version 18.09, Docker supports a new backend for executing your builds that is provided by the moby/buildkit project. The BuildKit backend provides many benefits compared to the old implementation. For example, BuildKit can: Detect and skip executing unused build stages Parallelize building independent build stages Incrementally transfer only the changed files in your build context between builds Detect and skip transferring unused files in your build context Use external Dockerfile implementations with many new features Avoid side-effects with rest of the API (intermediate images and containers) Prioritize your build cache for automatic pruning.
In order to select this backend, we export the environment variable DOCKER_BUILDKIT=1. If you miss the detailed output, just add --progress=plain.

Use multi-stage builds

We are used to seeing a lot of trickery to try to keep each layer size to a minimum. Very often we use a RUN statement to download the source and build an artifact, for instance a .deb file or to compile a binary, and try to clean it up in the same statement to keep the layer tidy.

    apt-get update ; \
    DEBIAN_FRONTEND=noninteractive apt-get install --no-install-recommends -y git make gcc libc-dev ; \
    git clone https://github.com/some_repo ; \
    cd some_repo ; \
    ./configure ; \
    make ; \
    make install; \
    cd -; \
    rm -rf some_repo; \
    apt-get purge -y make gcc libc-dev git; \
    apt-get autoremove -y; \
    apt-get clean; \
    find /var/lib/apt/lists -type f | xargs rm; \
    find /var/log -type f -exec rm {} \;; \
    rm -rf /usr/share/man/*; \
    rm -rf /usr/share/doc/*; \
    rm -f /var/log/alternatives.log /var/log/apt/*; \
    rm /var/cache/debconf/*-old

This both wastes time each build and is ugly for what it does. It is better to use multi-stage builds.

FROM debian:stretch-slim AS some_bin
RUN apt-get update; \
    DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-    recommends git make gcc libc-dev; \
    git clone https://github.com/some_repo; \
    cd some_repo; \
    ./configure; \
FROM debian:stretch-slim
COPY --from=some_bin /root/some_repo/some_bin /usr/local/bin/

In some cases, in order to avoid this I have seen people adding a binary blob in the git repository so it can be copied. Much better to use this approach.

Use –squash

While it doesn’t always makes sense for every Dockerfile, we can often squash our first layer and achieve a more maintainable Dockerfile.

--squash is an experimental argument that needs to be enabled like we explained here. Instead of

RUN apt-get update; \
    DEBIAN_FRONTEND=noninteractive apt-get install --no-install-recommends -y mariadb; \
    apt-get autoremove -y; \
    apt-get clean; \
    find /var/lib/apt/lists -type f | xargs rm; \
    find /var/log -type f -exec rm {} \;; \
    rm -rf /usr/share/man/*; \
    rm -rf /usr/share/doc/*; \
    rm -f /var/log/alternatives.log /var/log/apt/*; \
    rm /var/cache/debconf/*-old

, we can do

RUN apt-get update
RUN DEBIAN_FRONTEND=noninteractive apt-get install --no-install-recommends -y mariadb
RUN apt-get autoremove -y
RUN apt-get clean
RUN find /var/lib/apt/lists -type f | xargs rm
RUN find /var/log -type f -exec rm {} \;
RUN rm -rf /usr/share/man/*
RUN rm -rf /usr/share/doc/*
RUN rm -f /var/log/alternatives.log /var/log/apt/*
RUN rm /var/cache/debconf/*-old

Use one Dockerfile for all architectures

We talked about a technique to use qemu-user-static for creating builds for different architectures in a past article. When building different versions of the same image for different architectures, it is very common to see three exact copies of the same Dockerfile where the only thing that changes is the FROM line.

FROM debian:stretch-slim
# the rest of the file is duplicated

FROM armhf/debian:stretch-slim
# the rest of the file is duplicated

FROM arm64v8/debian:stretch-slim
# the rest of the file is duplicated

Just have one single file like so

ARG arch
FROM ${arch}/debian:stretch-slim

, and build with

docker build . --build-arg arch=amd64
docker build . --build-arg arch=armhf
docker build . --build-arg arch=arm64v8

Use multi-arch manifests

So we now have three builds with one Dockerfile, and we tag them like this

docker build . --build-arg arch=amd64   -t ownyourbits/example-x86
docker build . --build-arg arch=armhf   -t ownyourbits/example-armhf
docker build . --build-arg arch=arm64v8 -t ownyourbits/example-arm64

That’s all good, but we can now simplify the instructions the user has to type by creating a multi-arch manifest.

This is still an experimental CLI feature, so we need to export DOCKER<em>CLI</em>EXPERIMENTAL=enabled to be able to access it.

docker manifest create --amend ownyourbits/example \
  ownyourbits/example-x86 \
  ownyourbits/example-armhf \
docker manifest annotate ownyourbits/example ownyourbits/example-x86   --os linux --arch amd64
docker manifest annotate ownyourbits/example ownyourbits/example-armhf --os linux --arch arm
docker manifest annotate ownyourbits/example ownyourbits/nextcloudpi-arm64 --os linux --arch arm64v8
docker manifest push -p ownyourbits/example

Now your users of any architecture only have to do

docker pull ownyourbits/example

, and they will receive the correct version of the image.


Even if we run with --restart=unless-stopped, the only clue Docker or Docker Swarm to know that things are OK is that the container has not crashed. If it is unresponsive or returning errors it won’t be restarted properly.

It is more robust to add a HEALTHCHECK statement to the Dockerfile

HEALTHCHECK CMD curl --fail http://localhost:8080/status || exit 1

Don’t run as root

Even though containers are theoretically isolated, it is not good security practice to run processes as root inside them in the same way as you don’t run your web server as root.

Towards the end of your build you should add something like

    # other stuff
    useradd nonroot
USER nonroot

Also, if possible avoid relying on sudo and if you don’t control the Dockerfile at least run in a different user namespace with docker run -u nonroot:nonroot.

Don’t forget to build with –pull

Use docker build --pull in your scripts so you are always on the latest base image.


MAINTAINER is deprecated. Instead of

MAINTAINER nachoparker (nacho@ownyourbits.com)

, use LABELs instead so they can be inspected just like any other metadata.

LABEL maintainer="nachoparker (nacho@ownyourbits.com)"

Avoid ENV where possible

ENV variables remain in the container at run time and pollute its own environment. Use ARGs instead.

Build with cache mount

Speed up your builds by providing a cache for your package manager, ccache, git and so on. This needs to be enabled with DOCKER<em>CLI</em>EXPERIMENTAL=enabled

# syntax=docker/dockerfile:experimental
# FROM and the rest
RUN --mount=type=cache,target=/var/cache/apt --mount=type=cache,target=/var/lib/apt \
    apt-get install -y --no-install-recommends mongodb-server

Use SSH agent

If you require SSH credentials for your build don’t copy ~/.ssh because it will stay in the layer even if you remove it later.

Set up SSH agent, and use the experimental feature for ssh mounts

RUN --mount=type=ssh git clone https://github.com/private_repo/repo.git

Use build secrets

If you need sensitive files that should not be public for your build, use secrets. This way, those files will only be visible to that RUN command during its execution and its contents will disappear without a trace from all layers after that.

RUN --mount=type=secret,id=signing_key,dst=/tmp/sign.cert signing_command

Read the official recommendations again

While I pointed out what for me are the biggest offenders, it is always good to go back and review the officially recommended best practices.

Most of them we are familiar with: write small containers, rearrange layers to take advantage of build cache, don’t add unnecessary packages, but it’s not uncommon to go back to it and discover something we might have missed before.

*Originally published by *nachoparker *at *ownyourbits.com

#docker #web-development

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How to build a Docker container for beginners
Iliana  Welch

Iliana Welch


Docker Tutorial for Beginners 8 - Build and Run C++ Applications in a Docker Container

Docker is an open platform that allows use package, develop, run, and ship software applications in different environments using containers.
In this course We will learn How to Write Dockerfiles, Working with the Docker Toolbox, How to Work with the Docker Machine, How to Use Docker Compose to fire up multiple containers, How to Work with Docker Kinematic, Push images to Docker Hub, Pull images from a Docker Registery, Push stacks of servers to Docker Hub.
How to install Docker on Mac.

#docker tutorial #c++ #docker container #docker #docker hub #devopstools

Mikel  Okuneva

Mikel Okuneva


Ever Wondered Why We Use Containers In DevOps?

At some point we’ve all said the words, “But it works on my machine.” It usually happens during testing or when you’re trying to get a new project set up. Sometimes it happens when you pull down changes from an updated branch.

Every machine has different underlying states depending on the operating system, other installed programs, and permissions. Getting a project to run locally could take hours or even days because of weird system issues.

The worst part is that this can also happen in production. If the server is configured differently than what you’re running locally, your changes might not work as you expect and cause problems for users. There’s a way around all of these common issues using containers.

What is a container

A container is a piece of software that packages code and its dependencies so that the application can run in any computing environment. They basically create a little unit that you can put on any operating system and reliably and consistently run the application. You don’t have to worry about any of those underlying system issues creeping in later.

Although containers were already used in Linux for years, they became more popular in recent years. Most of the time when people are talking about containers, they’re referring to Docker containers. These containers are built from images that include all of the dependencies needed to run an application.

When you think of containers, virtual machines might also come to mind. They are very similar, but the big difference is that containers virtualize the operating system instead of the hardware. That’s what makes them so easy to run on all of the operating systems consistently.

What containers have to do with DevOps

Since we know how odd happenings occur when you move code from one computing environment to another, this is also a common issue with moving code to the different environments in our DevOps process. You don’t want to have to deal with system differences between staging and production. That would require more work than it should.

Once you have an artifact built, you should be able to use it in any environment from local to production. That’s the reason we use containers in DevOps. It’s also invaluable when you’re working with microservices. Docker containers used with something like Kubernetes will make it easier for you to handle larger systems with more moving pieces.

#devops #containers #containers-devops #devops-containers #devops-tools #devops-docker #docker #docker-image

Docker Architecture Overview & Docker Components [For Beginners]

If you have recently come across the world of containers, it’s probably not a bad idea to understand the underlying elements that work together to offer containerisation benefits. But before that, there’s a question that you may ask. What problem do containers solve?

After building an application in a typical development lifecycle, the developer sends it to the tester for testing purposes. However, since the development and testing environments are different, the code fails to work.

Now, predominantly, there are two solutions to this – either you use a Virtual Machine or a containerised environment such as Docker. In the good old times, organisations used to deploy VMs for running multiple applications.

So, why did they started adopting containerisation over VMs? In this article, we will provide detailed explanations of all such questions.

#docker containers #docker engine #docker #docker architecture

Iliana  Welch

Iliana Welch


Docker Explained: Docker Architecture | Docker Registries

Following the second video about Docker basics, in this video, I explain Docker architecture and explain the different building blocks of the docker engine; docker client, API, Docker Daemon. I also explain what a docker registry is and I finish the video with a demo explaining and illustrating how to use Docker hub

In this video lesson you will learn:

  • What is Docker Host
  • What is Docker Engine
  • Learn about Docker Architecture
  • Learn about Docker client and Docker Daemon
  • Docker Hub and Registries
  • Simple demo to understand using images from registries

#docker #docker hub #docker host #docker engine #docker architecture #api

August  Murray

August Murray


Docker Swarm: Container Orchestration Using Docker Swarm


A swarm consists of multiple Docker hosts that run in swarm mode and act as managers (to manage membership and delegation) and workers (which run swarm services). A given Docker host can be a manager, a worker, or perform both roles.

When Docker is running in swarm mode, you can still run standalone containers on any of the Docker hosts participating in the swarm, as well as swarm services. A key difference between standalone containers and swarm services is that only swarm managers can manage a swarm, while standalone containers can be started on any daemon.

In this demonstration, we will see how to configure the docker swarm and how to perform basic tasks.


  1. For our demonstration, we will be using centos-07.
  2. We will be using 3 machines for our lab, 1 machine as a swarm Manager node and 2 swarm worker nodes. These servers have below IP details: managernode.unixlab.com workernode1.unixlab.com workernode2.unixlab.com

3. The memory should be at least 2 GB and there should be at least 2 core CPUs for each node.

#docker #containers #container-orchestration #docker-swarm