Top 7 Docker Alternatives

A container is a separate unit of software that encapsulates the software and libraries of an application, including its dependencies and its code.

As a means of developing and managing stable applications, many organisations are adopting containers. Millions of applications currently use Docker, one of the most useful tools in this space.

A Docker container can be used to build, run, inspect, and manage container images for developing applications. Docker is a Linux-based open-source containerization technology.

Docker is generally misunderstood to be only about containers.  There are many other projects that are part of the container ecosystem, and Docker is only part of the container ecosystem.

In addition to requiring compliance with open container initiatives (OCI) and Kubernetes Container Runtime Interfaces (CRI), the two are made up of two sets of standards.

Docker’s ecosystem is robust and provides an extensive toolkit for managing containerization processes, but there are other alternatives that extend beyond Docker.

As a drop-in replacement for the Docker ecosystem, we'll look at a few Docker alternatives in this article. Here we go!

Table Of Contents

1. Podman
2. BuildKit
3. Buildah
4. OpenVz
5. Kaniko
6. RunC
7. Containerd

#1 Podman

A virtualization platform offered by RedHat called Podman is an open-source alternative. The Podman container engine can be used on Linux machines to develop, maintain, and run OCI containers just like Docker.

It is, however, daemon-less and does not require root privileges to run the Podman Container Engine. By integrating directly with systemD (system daemon), Podman runs containers in the background without root privileges. Thus, Podman's Docker daemon functionality is taken over by the system.

Due to the fact that Podman is a daemon-less container engine, you have an excellent security advantage due to the fact that containers depend on user privileges.

The installation of Rootless Containers on User Namespaces will require additional features to run on your machine. So, you may be able to take advantage of Podman's more features.

Integrating other development tools might also be a reason to consider Podman. In comparison to Docker, which provides a compatible API that makes switching easy, Podman displays a wider range of integration with developer's tools.

From a security standpoint, Podman offers more protection. The fact that Podman is OCI-compliant, with Docker files and images supported, means that you can easily switch from Docker or other container engines to Podman.

Podman installation and basic commands

On Ubuntu 22.04 you can install Podman with the below command:

// ubuntu 22.04
sudo apt-get -y install podman

To install Podman in Ubuntu 20.04 or 18.04

. /etc/os-release

echo "deb https://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable/xUbuntu_${VERSION_ID}/ /" | sudo tee /etc/apt/sources.list.d/devel:kubic:libcontainers:stable.list

curl -L "https://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable/xUbuntu_${VERSION_ID}/Release.key" | sudo apt-key add -

Once the repository is added follow the below steps:

sudo apt update
sudo apt -y install podman

Ensure Podman has been correctly installed by checking the Podman version and other information.

podman info

podman --help

podman <subcommand> --help

Search, Pull and List Images

Search: Use the below command to search for the images.

podman search <search_term>

// example
podman search httpd

Pull: You can also pull images using the command pull.

podman pull docker.io/library/httpd

List: Below command helps you in listing the pulled images.

podman images

To run a container

The sample container will run a container and serve a basic index page in the httpd server.

podman run -dt -p 8080:80/tcp docker.io/library/httpd

The ps command along with podman is used to list all the created images.

podman ps

#2 BuildKit

A built-in image-building feature is also provided as an experimental functionality in updated versions of Docker called BuildKit. The daemon is similar to that used by Docker.

A new image-building engine for Docker has been developed by the Moby team as part of their project called Buildkit.

A key difference between the standard Docker build and BuildKit is that the latter provides parallel builds instead of building each layer individually. Adding this feature speeds up builds and improves performance.

Additionally, it permits rootless builds, skipping unused stages, and improving incremental builds. In addition, each layer of an image is reduced in size by using a cache.

Installation of BuildKit

A fresh installation of Docker can be achieved by setting the DOCKER_BUILDKIT=1 environment variable when executing the docker build command, as pursues:

$ DOCKER_BUILDKIT=1 docker build .

The Docker BuildKit is enabled by default, the daemon configuration is set to true in /etc/docker/daemon.json, and the daemon must be restarted:

{ "features": { "buildkit": true } }

In order to apply the changes, reload the daemon after saving the file:

$ systemctl reload docker

A distinct difference between the default engine and Buildkit's output can be detected when Buildkit is used:

sudo DOCKER_BUILDKIT=1 docker build .
[+] Building 0.7s (7/7) FINISHED
 => [internal] load build definition from Dockerfile                   
 => => transferring dockerfile: 82B
 => [internal] load .dockerignore
 => => transferring context: 2B
 => [internal] load metadata for docker.io/library/nginx:latest
 => [internal] load build context
 => => transferring context: 31B
 => [1/2] FROM docker.io/library/nginx
 => [2/2] COPY nginx.conf /etc/nginx
 => exporting to image
 => => exporting layers
 => => writing image

#3 Buildah

As an alternative to Docker, Buildah allows you to create images. In addition to Podman, Buildah is also developed by RedHat.

The container management instrument is also designed by RedHat, which developed the Podman container management tool. It uses a fork-exec method that enables executing containers without having to run them from a central daemon.

Buildah permits you to implement many changes at one level, in contrast to Docker. As an additional feature, it incorporates the ability to create a container image with empty metadata. As a result, its final product is inferior to that of Docker.

#4 OpenVz

Virtuozzo's OpenVz containerization technology is Linux-based and similar in features and functionality to Docker, but its ability to deploy applications goes beyond Docker.

On a single Linux host, OpenVz can be used to create multiple isolated Linux containers. Consequently, Linux-based containers are used for hosting virtual servers in an isolated environment (most VPN-enabled virtual private servers will use OpenVz containers).

One of the most important features associated with OpenVz is its Network File System (NFS). The user can access OpenVz virtual servers' network disk files through this feature.

Due to the NFS support for real-time migrations for IA64 processors, system or network administrators can use it to share or move virtual servers between two or more physical servers.

It is a powerful virtual platform for hosting containers and also doubles as a hypervisor for hosting virtual servers and offering a variety of services, including dedicated support, management tools and distributed cloud storage.

Installation of OpenVz

The following steps should be performed inside the container.

Getting Docker installed:

yum -y install docker-io

Launch the Docker daemon

dockerd -s vfs

Alternatively, add the following line to /etc/sysconfig/docker:

OPTIONS='--selinux-enabled -s vfs'

#5 Kaniko

An image-building tool built by Google that uses Docker files is called Kaniko. This is a daemon-less alternative to Buildah, focusing more on Kubernetes-based image building.

As Kaniko runs as an image with a container orchestrator such as Kubernetes, it is not very convenient for local development instances. However, Kaniko can be useful in Kubernetes clusters for continuous integration and delivery pipelines.

Using Kaniko to create a Docker image

There are a few things you should be aware of when creating an image with Kaniko and GitLab CI/CD:

1. Using kaniko debug image (gcr.io/kaniko-project/executor:debug) brings the benefit of having a shell, which is necessary for GitLab CI/CD integration.
2. Otherwise, the build script won't run since the entry point needs to be      overridden.

Here are some examples of how kaniko is used:

1. Create a Docker image.
2. It should then be pushed to the GitLab Container Registry.

A tag must be pushed to trigger the job. In /kaniko/.docker, a config.json file is created with the GitLab Container Registry credentials taken from the standard variables that GitLab CI/CD offers. The Kaniko tool automatically reads these.

The final step is for Kaniko to use the Dockerfile under the root directory of the project, to build the Docker image and tag it with the Git tag, before pushing it to the project's Container Registry:

build:
  stage: build
  image:
    name: gcr.io/kaniko-project/executor:v1.9.0-debug
    entrypoint: [""]
  script:
    - /kaniko/executor
      --context "${CI_PROJECT_DIR}"
      --dockerfile "${CI_PROJECT_DIR}/Dockerfile"
      --destination "${CI_REGISTRY_IMAGE}:${CI_COMMIT_TAG}"
  rules:
    - if: $CI_COMMIT_TAG

The config.json file needs to contain the following CI/CD variables for authentication when using the Dependency Proxy:

- echo "{\"auths\":{\"$CI_REGISTRY\":{\"auth\":\"$(printf "%s:%s" "${CI_REGISTRY_USER}" "${CI_REGISTRY_PASSWORD}" | base64 | tr -d '\n')\"},\"$CI_DEPENDENCY_PROXY_SERVER\":{\"auth\":\"$(printf "%s:%s" ${CI_DEPENDENCY_PROXY_USER} "${CI_DEPENDENCY_PROXY_PASSWORD}" | base64 | tr -d '\n')\"}}}" > /kaniko/.docker/config.json

#6 RunC

As a standalone tool, RunC was released in 2015 as an embedded tool within the Docker architecture. With time, it has evolved into a widely used, well-established, and highly scalable container runtime that is used with Docker as well as other custom container engines.

RunC constitutes a container runtime, as part of the containerization ecosystem. When containers are run by a container engine, the container runtime is responsible for handling the running of containers.

Despite Docker's comprehensive toolkit, some DevOps functions may require alternative solutions for various reasons, even though Docker offers a comprehensive toolkit for every aspect of containerization.

Nevertheless, when choosing any of these alternatives, the host OS and its use cases need to be taken into consideration.

.run package installation process

Advisory

Whenever anything is installed outside of the official repositories, it must be carefully considered. Software can be installed via a script rather than through a package manager with run files. Make sure the run file you obtained came from a reliable source before you execute it.

Installation

The following steps will guide you through the installation of software packaged in a .run file:

GUI

1. Use the File Browser to find the .run file.
2. You can access the file's properties by right-clicking it.
3. Press Close after ticking Allow executing file as program under the Permissions tab.
4. To open the .run file, double-click it. It should display a dialog box.
5. Run the installer by pressing Run in Terminal.
6. Upon opening, a Terminal window will appear. In order to install the program, follow the instructions on the screen.

Command-Line

The file can be found in the directory that you open with the terminal.

1. Perform chmod +x <file-to-give-execute-permission>.run
2. After setting the execute permission, simply run ./<file>.run

#7 Containerd

Containerd is a standalone container runtime with several features, such as scalability, durability, and adaptability. Container services are provided by Docker. An announcement was made by Docker on February 28, 2019, that it would become a standalone component.

Containerd is a free service that customers can use as part of their projects. Nonetheless, it was previously part of Docker's system before it became autonomous.

It does not require you to install Docker; it can be run using Runc without it. However, Containerd will be installed automatically when Docker is installed. Using Containerd's API, you can orchestrate containers in virtual environments with complete control.

The platform offers you a variety of capabilities, including push and pulls, handling containers, performing applications using image management APIs, organising snapshots, and much more.

Portability, as well as compatibility with Windows and Linux, make it a great choice for many users. Simplicity, robustness, and portability comprise its mission, along with its ability to run container life cycles all on its own.

Installation of containerd

Step 1: Install containerd

You can download the containerd-<VERSION>-<OS>-<ARCH>.tar.gz archive here, ascertain its sha256sum, and unpack it under /usr/local:

$ tar Cxzvf /usr/local containerd-1.6.2-linux-amd64.tar.gz
bin/
bin/containerd-shim-runc-v2
bin/containerd-shim
bin/ctr
bin/containerd-shim-runc-v1
bin/containerd
bin/containerd-stress

Linux distributions using the glibc library, such as Ubuntu and Rocky Linux, generate the containerd binary dynamically. Alpine Linux may not be able to run this binary since musl-based distributions don't support this binary. The source code of containerd may have to be installed with such distributions, or a package from a third party may be required.

systemd

To start containerd via systemd, you need to download the containerd.service unit file here, and run the following commands:

systemctl daemon-reload
systemctl enable --now containerd

Step 2: Install runc

Install runc.<ARCH> from the documentation, verify its sha256sum, and run it from /usr/local/sbin/runc.

$ install -m 755 runc.amd64 /usr/local/sbin/runc

Linux distributions should work with the binary since it is built statically.

Step 3: Install CNI plugins

Get the cni-plugins-<OS>-<ARCH>-<VERSION>.tgz archive from the plugins release, double-check its sha256sum, and unzip it under /opt/cni/bin:

$ mkdir -p /opt/cni/bin
$ tar Cxzvf /opt/cni/bin cni-plugins-linux-amd64-v1.1.1.tgz
./
./macvlan
./static
./vlan
./portmap
./host-local
./vrf
./bridge
./tuning
./firewall
./host-device
./sbr
./loopback
./dhcp
./ptp
./ipvlan
./bandwidth

Linux distributions should be able to run the binaries since they are built statically.

Recapitulate: Is There A Smarter Docker Alternative?

The Docker platform is an open-source platform used to design, test, deploy, and handle applications. There is a notable feature of Docker that allows users to share virtual production environments known as containers.

Docker containers have, however, been criticized by some developers because they present challenges when developing applications.

A number of Docker alternatives have been developed to address some of these challenges in a virtualised platform that is in many ways more powerful than Docker itself.

Docker alternatives 2022 can be useful if you are having problems using Docker. There are a variety of open-source alternatives that are easy to use. Besides offering the same level of functionality and features, they also offer more.

In order to overcome Docker's pitfalls, they were incorporated. You can go through the above features and choose based on your requirement.

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