Docker in DevOps: Use Cases & How Does it Work?

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StarAgile

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Oct 16, 2023

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The IT industry is constantly evolving, with new technologies emerging rapidly. One of the latest innovations that have revolutionized the DevOps landscape is Docker. Docker is an open platform for developing, shipping and running applications. It has made life easier for developers and system administrators by simplifying the deployment of applications. Docker utilizes OS-level virtualization to deliver software in packages called containers.

Docker containers are lightweight, standalone, executable packages of software that include everything required to run an application: code, runtime, dependencies, and config files. By containerizing applications, Docker has paved the way for improved collaboration between developers and IT operations teams. It has become essential for continuous integration and deployment (CI/CD) pipelines.

 

Let's explore Docker in more detail and understand why it is indispensable for DevOps.

 

What is Docker?

Docker is an open-source containerization platform that allows developers to package an application with all of its dependencies into a standardized unit for software development. 

Containers include the application code and all of its dependencies, but share the host operating system kernel, so they are more lightweight than virtual machines.

Docker uses a client-server architecture. 

The Docker daemon runs on a host operating system like Linux or Windows and does the containers' actual building, running, and distributing. 

The Docker client interfaces with the daemon through CLI or REST API to give commands and configuration.

Docker's container-based platform is essential for DevOps because it enables fast, automated deployment of applications. 

Containers can be built locally, pushed to a container registry, and then deployed to any infrastructure. 

The container abstraction significantly eases migrating applications between environments because the container includes all dependencies packaged together with the app.

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Why is Docker essential for DevOps?

Some key benefits of Docker for Data Science are:

  • Fast, consistent deployments

Docker's container-based platform allows you to create automated build and deployment workflows. 

When an update is pushed, Docker can automatically rebuild the container, run any required tests, and release the new version. 

This enables continuous integration and deployment.

  • Environment standardization

Docker containers encapsulate all their dependencies and configuration. 

This means an application will run the same regardless of where the container is deployed. 

There are no more environment-specific configurations to manage, which reduces bugs related to environment inconsistencies.

  • Portability

Docker containers and images are entirely portable. 

You can build locally, deploy to the cloud, and run anywhere. 

This allows a "build once, run anywhere" workflow, which is ideal for DevOps. 

  • Scalability

It is easy to scale Dockerized applications by spinning up or tearing down additional containers. 

This facilitates an easy path to scale up or down in response to demand changes.

  • Isolation

Docker containers run in a separate space and have their own filesystem, CPU, memory, process space, and network interfaces. 

This isolation allows you to run many containers on a single host.

  • Tooling and automation

Docker includes many tools to facilitate automated workflows. All of these tools allow DevOps engineers to build automation and tools around the Docker platform.

    • Docker Compose for running multi-container applications 
    • Docker Registry for storing and sharing container images
    • Docker Desktop includes Kubernetes for container orchestration 
    • Docker in Docker for nested container workflows

Docker provides a powerful platform for developing, testing and deploying containerized applications. For DevOps, Docker opens up many possibilities for creating automated, scalable workflows to build, release and maintain applications. With its vast ecosystem of tools and services, Docker addresses many of the challenges DevOps teams face in standardizing and optimizing the application lifecycle.

Using Docker, developers can build container images that contain their application and all dependencies and deploy them into any environment. This allows creating consistent and automated workflows for building, testing, and releasing software.

An essential continuous integration and deployment workflow with Docker would be:

1. Developer commits code to a version control system, which triggers a build in the CI system.

2. The CI system does a Docker build from the Dockerfile, creating a new container image. 

3. The CI system runs any required unit or integration tests on the new image.

4. If the tests pass, the CI system pushes the newly built image to a Docker registry.

5. The CI system deploys the new image by spinning up the container on a target environment (dev, staging, prod). 

6. The CI system can monitor the health/logs of the deployed container and roll back if needed.

This type of automated build, test, and deployment pipeline enabled by Docker is crucial for DevOps. It allows the creation of a standardized and efficient workflow for updating and maintaining applications. Docker provides the perfect platform for containerizing applications and linking them into modern CI/CD toolchains and pipelines.

For any DevOps team aiming to automate application deployment and gain the benefits of containers fully, Docker is an essential technology to learn and master. 

With its open-source, community-driven tools and platform, Docker allows DevOps engineers to focus on optimizing application lifecycle workflows rather than maintaining infrastructure.

By enabling fast, consistent deployments across environments, Docker is a game changer for DevOps.

Key Docker concepts

  • Images

A Docker image is a read-only template with instructions for creating a Docker container. Images are built from Dockerfiles and contain a set of predefined layers that make up an image. Images can be shared via Docker registries like Docker Hub.

  • Containers

A Docker container is a runtime instance of an image. Containers run the application in an isolated environment and have their own filesystem, CPU, memory, process space, and network interfaces. However, they share the host OS kernel, so they are more lightweight than VMs. Containers can be started, stopped, committed (converted into images), and deleted.

  • Dockerfile

A Dockerfile is a text document with instructions for building a Docker image. It contains a set of commands and arguments that Docker follows to auto-generate a Docker image. Using a Dockerfile, you can create an image containing your application and all its dependencies.

  • Docker Hub

Docker Hub is a SaaS service provided by Docker for sharing and managing Docker images. It is a public Docker registry with thousands of images that can be downloaded and used locally. You can also push your own images to Docker Hub to share with others.

  • Docker Registry

A Docker registry stores Docker images. Docker Hub is Docker's public registry service, but you can also set up private registries to store and share images internally within your organization. 

  • Docker Compose

Docker Compose is a tool for defining and running multi-container Docker applications. With Docker Compose, you use a YAML file to configure your application's services, and then you can start all the services with a single command. Docker Compose is helpful for development environments where you want to combine multiple services.

  • Docker Engine

The Docker Engine powers the Docker platform. It consists of a Docker daemon, a CLI, and a REST API. The Docker daemon is what actually builds, runs, and manages Docker containers. The Docker CLI and REST API allow you to interact with the Docker daemon.

How does Docker work?

  • Docker runs on a host operating system like Linux or Windows. When you run an image and launch a container, Docker creates a virtual environment for the container with its own filesystem, CPU, memory, process space, and network interfaces. However, the containers share the host OS kernel, so they are more lightweight than VMs.
  • When you run a container from an image, the container gets its own filesystem, which is a thin writable layer over the read-only image. 
  • The container's processes are isolated and have their own process ID space.  Network interfaces and routing tables are created for each container. 
  • However, the container shares the host's kernel with other containers and runs in a separate namespace. This allows containers to be lightweight while still isolated from one another.

Docker vs Virtual Machines

Docker containers and virtual machines are two different technologies that are often used for similar purposes. While Docker and VMs provide some similar benefits like environment isolation and package deployment, Docker's container-based architecture is generally more lightweight, portable, and better suited for rapid development processes. However, VMs may still be preferable over containers for some use cases requiring maximum security isolation.

While both Docker containers and VMs provide isolated application environments, there are some key differences:

Docker ContainersVirtual Machines
Docker containers are more lightweight than VMs.VMs require a full OS
Docker can run on any systemVMs require a hypervisor like VirtualBox or VMware to run the guest VMs. 
Docker images can be shared via registriesVMs are not easily shareable
Docker uses a "build once, run anywhere" philosophyVMs require installing and configuring a guest OS for each environment
Docker enables fast, iterative development workflows. It is easy to spin up, modify, and tear down containers quicklyVMs are slower to boot and shut down
Docker can run many more isolated environments on a single host compared to VMsVMs cannot run in isolated environments.

 

Benefits of using Docker in DevOps

Fast and efficient deployments

Docker's lightweight containers enable rapid development and deployment workflows. You can quickly build, test, and produce applications.

Portability

Docker containers and images are portable and can run anywhere - on your local machine, data center VMs, the cloud, bare metal, etc. This enables a "build once, run anywhere" approach.  

Scalability

It's easy to scale containerized applications up or down by spinning up or tearing down containers.

Isolation

Containers run in isolated environments and don't interfere with one another. This facilitates running many workloads on a single host.

Productivity

The Docker platform has many tools and services to facilitate efficient workflows. This productivity gain allows developers to focus on building applications rather than environment configuration. 

Environment standardization

Docker helps ensure consistency between environments. Your application will run the same regardless of where it's deployed, reducing environment-related bugs.

Security

Docker applies kernel namespaces and control groups to containers for workload isolation. This improves security over running applications directly on the host.

Use cases of Docker

Docker enables several major benefits for application development and deployment, especially in the era of cloud and microservices architectures. With its lightweight container technology and build once, run anywhere philosophy, Docker facilitates fast, scalable, and portable application development workflows.

  • Continuous integration and deployment

Docker is ideal for spinning up ephemeral testing, building, and deployment environments. It allows you to automatically build, test, and release containerized applications through continuous integration pipelines.

  • Microservices

Docker's isolated containers work well for deploying microservices applications. Each service can run in its own container, and the containers can be scaled independently based on demand for each service.

  • Portability and isolation

If you need to isolate your application environments or run your applications across different infrastructure environments, Docker is a great choice. Your containers will run the same regardless of platform or cloud provider.

  • Development environments

Docker allows you to quickly spin up development environments with all the necessary dependencies and tools. This boosts productivity for developers and ensures consistency across environments.

  • Web applications

Docker is a popular option for deploying web applications. You can use containers to scale web applications and ensure portability across platforms automatically.

Getting Started with Docker

  • Install Docker on your local machine or server. You can download Docker Community Edition for Mac, Windows, or Linux.
  • Write a Dockerfile to build your first image. A basic Dockerfile would be:

```

FROM ubuntu:18.04 

RUN apt-get update && apt-get install -y nginx

CMD ["nginx", "-g", "daemon off;"]

```

This will install Nginx in an Ubuntu image.

  • Build the image from your Dockerfile:

`docker build -t mynginx:1.0 .`

  • Run a container from the image: 

`docker run -p 8080:80 mynginx:1.0`

This will launch an Nginx container on port 8080.

  • Share your image on Docker Hub:

`docker push myusername/mynginx:1.0`

  • Pull the image on another machine and run it:

`docker run -p 8080:80 myusername/mynginx:1.0`

  • Explore other Docker commands like `docker logs`, `docker stop`, `docker cp`, etc. 

 

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Conclusion

Docker is a powerful tool for DevOps teams looking to simplify the process of deploying and managing applications. Certification like Devops courses, devops training, and devops certification can help you understand docker better. By using Docker containers, developers can create a consistent environment for their applications, regardless of the underlying infrastructure. 

Docker also provides several other benefits, including faster application deployment, improved scalability, and increased portability. Whether you're deploying microservices, creating development environments, or testing applications, Docker can help streamline your DevOps workflows and improve your overall productivity. So if you haven't already, try Docker and see how it can benefit your DevOps team today!

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