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Docker and Containerization Concepts

Docker is an open-source platform that enables teams to build, package, and deploy applications using lightweight and portable containers.

By packaging an application together with its dependencies into a standardized unit called a container, Docker ensures consistent behavior across development, testing, and production environments. This approach eliminates common environment-related issues and improves overall DevOps efficiency.

Docker is commonly used to develop microservices-based applications, optimize CI/CD pipelines, and run isolated and reproducible software environments.

Docker Architecture​

Docker follows a client-server architecture and consists of the following core components.

Docker Engine​

Docker Engine is the runtime responsible for building, running, and managing containers. It includes:

  • Docker Daemon (dockerd): A background service that runs on the host system and manages images, containers, networks, and volumes.
  • Docker CLI (docker): A command-line interface that allows users and automation tools to interact with the Docker Daemon.
  • Docker API: A REST API used by the Docker CLI and third-party tools to communicate with the Docker Daemon.

Docker Objects​

  • Docker Image: A read-only template that contains application code, dependencies, and runtime configuration. Images serve as the blueprint for containers.
  • Docker Container: A runnable instance of a Docker image. Containers provide isolated execution environments while sharing the host operating system kernel. This makes them more lightweight and faster to start than traditional virtual machines.

Core Docker Concepts​

Images: Docker images are composed of multiple layers that represent incremental changes to an application environment. Images are built using a Dockerfile, which defines instructions such as the base image, files to include, and commands to execute. Images are stored in container registries such as Docker Hub or private enterprise registries.

Containers: Containers are runtime instances of images that are portable, isolated, and efficient. They include everything an application needs to run while sharing the host operating system kernel. Common Docker CLI commands used to manage containers include:

docker run <image>
docker stop <container>
docker rm <container>

Volumes: Docker volumes provide persistent storage for containers. Since container file systems are ephemeral by default, volumes ensure that data remains available even after a container is stopped or removed.

docker volume create my_volume
docker run -v my_volume:/app/data my_image

Networks: Docker networking enables communication between containers and external systems. Docker provides multiple built-in network drivers, including:

  • bridge (default)
  • host
  • overlay
  • macvlan

Custom networks allow containers to discover and communicate with each other using DNS-based service names.

Dockerfile: Dockerfile defines the steps required to build a Docker image. It ensures repeatable and automated image creation. A simple example is shown below:

FROM node:18
WORKDIR /app
COPY . .
RUN npm install
CMD ["node", "server.js"]

This Dockerfile produces a consistent and portable runtime environment for the application.

Docker Compose: Docker Compose is used to define and manage multi-container applications. It relies on a YAML configuration file (docker-compose.yml) to describe services, networks, and volumes. Docker Compose is commonly used for local development and integration testing.

version: "3"
services:
  web:
    build: .
    ports:
      - "5000:5000"
  redis:
    image: "redis:alpine"

You can start the entire stack with the following command:

docker-compose up

Benefits of Docker​

  • Consistency Across Environments: The same container image is used across development, staging, and production.
  • Simplified Configuration Management: Environment variables, volumes, and configuration files are easy to manage and reproduce.
  • CI/CD Integration: Docker integrates seamlessly with continuous integration and delivery systems.
  • Resource Efficiency: Containers consume fewer resources than virtual machines due to shared kernel usage.
  • Rapid Deployment: Containers can be built and started quickly, enabling faster release cycles.
  • Portability: Containers run consistently across on-premise, cloud, and hybrid environments.
  • Isolation: Each container runs independently, reducing dependency conflicts.
  • Scalability: Containers work well with orchestration platforms such as Kubernetes.
  • Security: Application isolation adds an additional security boundary between workloads.

Docker Integration in BuildNinja​

BuildNinja uses Docker in three primary ways: as a build environment for compiling and packaging applications, as a deployment target for containerized workloads, and as the hosting platform for the BuildNinja Server and Agent.

Docker Image Build Support​

BuildNinja can build Docker images as part of CI using the Command Line Runner. Build steps can execute docker build and docker push commands to package applications and publish images to a container registry such as Docker Hub, a private registry, or cloud registries including AWS ECR or Azure Container Registry.

This workflow is explained in detail in the How to Build a Docker ImageConfigure a build configuration in BuildNinja to package your application source code into a Docker container image. This guide explains how to build the image and optionally push it to a container registry so it can be … guide.

Container Deployment Support​

After an image is published to a registry, a downstream Build Configuration can deploy it using docker pull and docker run, or by deploying through Kubernetes. These commands are executed directly on the BuildNinja Agent using the locally installed Docker runtime, without requiring additional plugins.

Containerized BuildNinja Architecture​

BuildNinja Server and Agent can be deployed as Docker containers. This approach simplifies installation and enables fully containerized BuildNinja environments.

Detailed instructions are available in the Configure Server and Agent with Docker and KubernetesConfigure and deploy the BuildNinja Server and Agent using Docker for containerization and Kubernetes for orchestration. This setup ensures both components run in consistent, scalable, and portable environments across sy… guide.

Build Agent Docker Requirements​

The BuildNinja Agent must have Docker installed and the Docker Daemon running to run Docker-based build steps. If the agent itself runs inside a container, the host Docker socket must be mounted using:

-v /var/run/docker.sock:/var/run/docker.sock

This configuration enables Docker commands to be executed from within the agent container.

Next Steps​

  • How to Build a Docker ImageConfigure a build configuration in BuildNinja to package your application source code into a Docker container image. This guide explains how to build the image and optionally push it to a container registry so it can be …
  • Configure Server and Agent with DockerDocker provides an efficient and consistent way to deploy the BuildNinja Server and Agent using prebuilt Docker images. Running BuildNinja in containers simplifies setup, ensures environment consistency, and makes it eas…