Introduction to Containers

1. Traditional Computing Challenges in Software Development

Traditional computing environments pose several issues that hinder efficient software development and deployment:

• Lack of Application Isolation: Applications running on physical servers can interfere with each other due to shared resources.
• Resource Underutilization/Overutilization: Physical servers are either underused or overloaded, leading to poor ROI and performance bottlenecks.
• High Provisioning & Maintenance Costs: Setting up infrastructure is time-consuming and expensive.
• Limited Scalability: On-premises setups often lack the flexibility to scale rapidly during peak loads.
• Poor Portability: Applications built on one OS or environment may not work seamlessly in another.
• Manual Deployment Processes: Automation is difficult, especially when deploying across multiple platforms.

2. What Are Containers?

Containers are lightweight, isolated, portable units of software that encapsulate an application along with its runtime dependencies (libraries, binaries, system tools, and configuration files). They allow developers to build, ship, and run applications consistently across different computing environments.

Key Characteristics of Containers

• Lightweight: Containers share the host OS kernel and do not require a full OS per instance.
• Isolated: Each container runs in its own user space, preventing interference between apps.
• Portable: Can run on any platform supporting the container engine (cloud, desktop, on-prem).
• Consistent: Ensure “it works on my machine” doesn’t become a problem.
• Fast: Start almost instantly and use minimal memory.

3. Container Engine Functionality

A container engine virtualizes the operating system and manages the lifecycle of containers. It ensures that all required components (code, runtime, libraries) are bundled together and executed in isolation.

Examples:

• Docker
• Podman
• LXC
• Vagrant

4. Benefits of Containerization

5. Container Use Cases

• Microservices architecture
• Continuous Integration / Continuous Delivery (CI/CD)
• Hybrid and multi-cloud deployments
• Scalable web services
• Data processing pipelines

6. Container Challenges

Despite their benefits, containers also introduce challenges:

• Security Risks: Vulnerabilities in the host OS can affect all containers.
• Container Management Complexity: Managing thousands of containers at scale requires orchestration tools like Kubernetes.
• Legacy App Migration: Refactoring monolithic apps into containers can be complex and time-consuming.
• Right-Sizing: Determining optimal resource allocation for each container without over or under-provisioning.

7. Popular Container Vendors & Tools

8. Containers vs Virtual Machines (VMs) (Advanced Note)

9. Role in Cloud-Native Development

Containers are foundational to cloud-native development, enabling:

• Modularity (via microservices)
• Resilience and scalability
• Automated deployment via orchestration tools
• Infrastructure as code (IaC) integration

They align perfectly with modern practices such as GitOps, CI/CD, Infrastructure as Code (IaC), and immutable infrastructure.

10. Conclusion

Containers have revolutionized how software is developed, deployed, and managed. They provide a consistent, lightweight, and scalable solution for overcoming many limitations of traditional computing models. However, successful adoption requires addressing security, management, and architectural considerations.

As organizations move toward DevOps maturity, embracing containerization—alongside orchestration tools like Kubernetes—is essential for building robust, agile, and future-proof systems.

Further Reading & Tools

• Docker Hub: https://hub.docker.com
• Kubernetes: Orchestration for managing containerized applications at scale.
• Helm Charts: Package managers for Kubernetes deployments.
• OCI (Open Container Initiative): Standard for container formats and runtime.

Introduction to Docker

1. What is Docker?

Docker is an open-source platform introduced in 2013 that enables developers to develop, ship, and run applications inside containers — lightweight, isolated, and portable environments.

Key Features of Docker

• Built using the Go (Golang) programming language.
• Leverages Linux kernel features such as namespaces and cgroups for container isolation and resource control.
• Provides a consistent environment across development, testing, staging, and production.

2. Docker Architecture Overview

Components of Docker Engine

Underlying Technologies

• Namespaces: Isolate processes, networking, user IDs, etc., within each container.
  • pid, net, mnt, uts, ipc, user namespaces
• Control Groups (cgroups): Limit and monitor resource usage (CPU, memory, disk I/O).
• Union File Systems (UnionFS): Layers filesystems to build efficient image layers and copy-on-write behavior.

3. The Docker Process Flow

1. Develop Application Locally
2. Create a Dockerfile – Defines the image structure.
3. Build Image – Using docker build, creates a reusable image.
4. Push Image – To a registry like Docker Hub or private registry.
5. Pull Image – On another machine/environment.
6. Run Container – Using docker run to instantiate the image into a running container.
7. Orchestrate & Scale – Using Docker Compose or Kubernetes for multi-container apps and scaling.

4. Docker Ecosystem & Tools

5. Benefits of Docker Containers

6. Docker in DevOps Practices

Docker supports modern DevOps methodologies, including:

• Agile Development: Rapid iteration and deployment cycles.
• CI/CD Pipelines: Automated builds, tests, and deployments using Docker images.
• Immutable Infrastructure: Deploy new versions without modifying existing containers.
• GitOps: Sync infrastructure and application state with Git repositories using Helm + Kubernetes.

7. Challenges of Docker Containers

8. When NOT to Use Docker

Avoid Docker if your application:

• Requires high performance or low-latency execution.
• Depends heavily on native hardware access.
• Is a monolithic legacy app difficult to modularize.
• Uses rich GUI interfaces (e.g., traditional desktop apps).
• Has strict security compliance requirements without proper hardening.

9. Real-World Use Cases

10. Conclusion

Docker has transformed how modern applications are developed, deployed, and maintained. Its ability to provide consistent, isolated, and portable runtime environments makes it a cornerstone of cloud-native and DevOps practices.

However, successful implementation requires understanding its strengths and limitations, especially when scaling, managing security, or integrating with orchestration tools like Kubernetes.

Further Reading & Resources

• Docker Documentation
• Docker Hub
• Docker Compose Reference
• OCI (Open Container Initiative)
• Kubernetes + Docker Integration

Building and Running Containers with Docker

1. Container Lifecycle Overview

The process of building and running containers follows a structured lifecycle:

1. Create a Dockerfile – Defines the blueprint for your container image.
2. Build an Image – Using docker build from the Dockerfile.
3. Run a Container – Instantiate the image into a running container using docker run.
4. Manage Images & Containers – Use commands like docker images, docker ps, docker push, and docker pull.

2. Dockerfile: The Blueprint of a Container

A Dockerfile is a text document that contains all the commands a user could call on the command line to assemble an image.

Sample Dockerfile

FROM ubuntu:latest
CMD ["echo", "Hello World"]

Key Dockerfile Instructions

3. Building a Docker Image

Command Syntax

docker build [OPTIONS] PATH

Example Command

docker build -t my-app:v1 .

• -t → Tags the image with a name and version.
• . → Build context (current directory).

What Happens During Build?

1. Docker reads the Dockerfile.
2. Each instruction creates a new layer in the image.
3. Layers are cached for faster rebuilds.
4. Final output: A tagged image ready to be run or pushed to a registry.

Verify Image Creation

docker images

This lists all local images including:

• Repository name
• Tag
• Image ID
• Created date
• Size

4. Running a Container

Command Syntax

docker run [OPTIONS] IMAGE[:TAG]

Example Command

docker run my-app:v1

This:

1. Creates a new container instance from the image.
2. Runs the default command (CMD in Dockerfile).
3. Outputs: Hello World

5. Managing Containers

Common Docker CLI Commands

6. Advanced Tips for Building Efficient Images

Best Practices

• Use multi-stage builds to reduce final image size.
• Prefer COPY over ADD unless you need archive extraction.
• Combine RUN commands to minimize layers.
• Use .dockerignore to exclude unnecessary files from build context.
• Always tag images meaningfully (<app-name>:<version> or <commit-hash>).

Multi-Stage Build Example

# Stage 1: Build
FROM golang:1.20 AS builder
WORKDIR /app
COPY . .
RUN go build -o myapp

# Stage 2: Runtime
FROM alpine:latest
COPY --from=builder /app/myapp /myapp
CMD ["/myapp"]

7. Real-World Workflow Example

Step-by-step CI/CD Integration

1. Developer commits code to Git.
2. CI pipeline triggers docker build.
3. Tests are run inside the container.
4. If tests pass, docker push to registry (e.g., Docker Hub, ECR).
5. Deployment system pulls image and runs it via docker run.

8. Troubleshooting Containers

• Check running containers:

  docker ps

• Inspect container details:

  docker inspect <container_id>

• View logs:

  docker logs <container_id>

• Enter a running container:

  docker exec -it <container_id> sh

9. Summary

Introduction to Docker Objects

1. Overview of Docker Objects

Docker uses several core objects to manage and run applications in containers. These include:

2. Dockerfile: The Foundation of an Image

A Dockerfile is a blueprint used to build a Docker image.

Essential Dockerfile Instructions

⚠️ Best Practice: Use .dockerignore to exclude unnecessary files from the build context.

3. Docker Images: Read-Only Templates

An image is a static, read-only snapshot that includes:

• Application code
• Runtime dependencies
• Libraries and binaries
• Configuration files

Image Layers

• Each instruction in the Dockerfile creates a new layer.
• Layers are cached — only changed layers rebuild, improving efficiency.
• Multiple images can share common layers, saving disk space and network bandwidth.

Image Naming Convention

Format:

[<registry-host>:<port>/]<repository>:<tag>

Example:

docker.io/ubuntu:18.04

📌 If the registry is omitted (e.g., nginx:latest), Docker defaults to Docker Hub (docker.io).

4. Containers: Runnable Instances of Images

A container is a live, running instance of a Docker image.

Key Features of Containers

• Writable Layer: On top of the read-only image layers, allowing runtime changes.
• Isolation: Containers are isolated from each other and the host OS.
• Portability: Can be moved across environments without configuration changes.

Common Container Operations

5. Docker Networking: Communication Between Containers

Docker provides virtual networks to allow containers to communicate securely.

Types of Docker Networks

Managing Networks

docker network create my-network
docker network ls
docker network inspect my-network

You can attach a container to one or more networks at runtime:

docker run --network=my-network my-app

6. Docker Storage: Managing Persistent Data

By default, data inside a container is ephemeral — it’s lost when the container is removed.

Persistent Data Options

Using Volumes

docker volume create my-data
docker run -v my-data:/app/data my-app

This mounts the volume my-data into /app/data inside the container.

7. Docker Plugins & Add-ons

Plugins extend Docker’s capabilities beyond its core features.

Popular Plugin Types

Plugins are usually managed via the Docker CLI or API and can be installed dynamically.

8. Summary of Docker Objects

9. Best Practices

• Always use meaningful tags for images (e.g., myapp:1.0, myapp:commit-abc123).
• Minimize layers by combining RUN commands.
• Use .dockerignore to avoid including unnecessary files in the build context.
• Prefer named volumes over bind mounts for production workloads.
• Use multi-stage builds to reduce image size.
• Secure your containers using user namespaces and least privilege principles.

Docker Architecture: A Comprehensive Overview

1. Docker Architecture Overview

Docker follows a client-server architecture, enabling developers to build, run, and manage containers across various environments.

Core Components of Docker Architecture

2. Docker Client

The Docker Client is the primary interface for interacting with Docker.

Key Features

• Accepts user input via:
  • Command Line Interface (CLI) – e.g., docker run, docker build
  • REST API – used by tools like CI/CD pipelines or GUI apps
• Sends commands to the Docker Daemon for execution.
• Can connect to:
  • Local Docker Daemon (same machine)
  • Remote Docker Daemon (over network)

🛠 Example CLI Command:

docker run hello-world

3. Docker Host (Server)

The Docker Host is where containers actually run. It runs the Docker Daemon (dockerd).

Main Responsibilities of Docker Daemon

• Listens for API requests from clients.
• Manages Docker objects such as:
  • Images
  • Containers
  • Networks
  • Volumes
  • Plugins
• Handles low-level operations like building, running, and distributing containers.

Key Technologies Used by Docker Daemon

4. Docker Registry

A registry is a centralized location where Docker images are stored and shared.

Types of Registries

Image Lifecycle in the Registry

1. Build: Developer creates an image using docker build.
2. Tag: Assign a name and version using docker tag.
3. Push: Upload image to registry using docker push.
4. Pull: Retrieve image from registry using docker pull.

📦 Example:

docker build -t my-app:v1 .
docker tag my-app:v1 registry.example.com/myteam/my-app:v1
docker push registry.example.com/myteam/my-app:v1

5. Containerization Process Flow

Here’s a step-by-step breakdown of how Docker builds and runs a container:

Step 1: Build Image

• Use a Dockerfile to define image structure.
• Run docker build to create a new image.

Step 2: Tag & Push Image

• Tag the image with a name and optional version.
• Push it to a local or remote registry using docker push.

Step 3: Pull Image on Target Machine

• If the image doesn’t exist locally, use docker pull to fetch it from the registry.

Step 4: Run Container

• Execute docker run <image-name> to start a container from the image.

Visual Workflow

[Developer Machine]
     ↓ (docker build)
[Docker Image Created]
     ↓ (docker push)
[Registry - Store Image]
     ↓ (docker pull)
[Production / Deployment Machine]
     ↓ (docker run)
[Running Container]

6. Communication Between Docker Components

Client ↔ Daemon

• Communication happens via:
  • Local Unix socket (default)
  • TCP over network (for remote hosts)
• Uses Docker CLI or Docker SDKs/APIs.

Daemon ↔ Registry

• Pulls and pushes images from/to public or private registries.
• Authenticates when accessing secured registries.

Daemon ↔ Daemon (Swarm Mode)

• In Docker Swarm or Kubernetes environments, daemons communicate with each other to manage services and orchestrate containers.

7. Docker Object Management

The Docker host manages several types of objects:

8. Summary Table

9. Best Practices

• Always tag images meaningfully (e.g., app:1.0, app:commit-hash).
• Use .dockerignore to reduce image size.
• Prefer multi-stage builds to minimize final image footprint.
• Secure your registry access with authentication and encryption.
• Monitor and log containers using centralized systems (e.g., Prometheus + Grafana, ELK stack).

Review of Docker Concepts and Understanding a Dockerfile

📚 Overview

Docker is a powerful platform that enables developers to build, ship, and run applications using containers — lightweight, isolated, and portable environments.

This guide will walk you through essential Docker concepts and how to understand and write a Dockerfile, the blueprint for building Docker images.

🧱 Key Docker Concepts

🛠️ Understanding a Dockerfile

A Dockerfile defines how to assemble a Docker image. Each instruction in a Dockerfile creates a new layer in the image.

✅ Sample Dockerfile (Node.js App)

# Use the official Node.js image as the base image
FROM node:14

# Set environment variables
ENV NODE_ENV=production
ENV PORT=3000

# Set the working directory
WORKDIR /app

# Copy package.json and package-lock.json files
COPY package*.json ./

# Install dependencies
RUN npm install --production

# Copy the rest of the application code
COPY . .

# Add additional file
ADD public/index.html /app/public/index.html

# Expose the port on which the application will run
EXPOSE $PORT

# Specify the default command to run when the container starts
CMD ["node", "app.js"]

# Labeling the image
LABEL version="1.0"
LABEL description="Node.js application Docker image"
LABEL maintainer="Your Name"

# Healthcheck to ensure the container is running correctly
HEALTHCHECK --interval=30s --timeout=10s --start-period=5s --retries=3 CMD curl -fs http://localhost:$PORT || exit 1

# Set a non-root user for security purposes
USER node

📋 Breakdown of Dockerfile Instructions

🔁 Docker Build & Run Process Flow

1. Write Dockerfile: Define all steps needed to build the image.
2. Build Image:

   docker build -t my-node-app:1.0 .

3. Tag Image: Optionally tag it for a specific registry.

   docker tag my-node-app:1.0 registry.example.com/myteam/my-node-app:1.0

4. Push to Registry: Share with others or deploy elsewhere.

   docker push registry.example.com/myteam/my-node-app:1.0

5. Pull Image: On another machine/environment.

   docker pull registry.example.com/myteam/my-node-app:1.0

6. Run Container:

   docker run -p 3000:3000 registry.example.com/myteam/my-node-app:1.0

🛡️ Best Practices for Writing Dockerfiles

• Use .dockerignore to exclude unnecessary files from the build context.
• Combine RUN commands where possible to reduce image layers.
• Use multi-stage builds to minimize final image size.
• Avoid running as root by using the USER directive.
• Label images for better traceability.
• Include health checks to monitor container status.
• Keep Dockerfiles clean and readable with comments.

📦 Summary

Hands On Lab: Pull, Build and Push the image to Docker Hub

🧾 Summary: Understanding the Benefits of Containers

✅ What is a Container?

• A container is a lightweight, standalone, and executable package that includes everything needed to run an application:
  • Code
  • Runtime
  • Libraries
  • Environment variables
  • Configuration files

Containers allow applications to run reliably across different computing environments.

🔧 Key Features & Benefits of Containers

🚀 Why Use Containers?

• Faster Deployment: Build once, deploy anywhere.
• Cost Efficiency: Better resource use means lower infrastructure costs.
• Automation & CI/CD: Easily integrate into DevOps pipelines.
• Microservices Architecture: Ideal for building scalable, distributed systems.
• Scalability: Quickly spin up or down containers based on demand.

🐳 About Docker

• Docker is the most popular platform for developing, shipping, and running containerized applications.
• It provides tools like:
  • docker build – To create images
  • docker run – To start containers
  • docker push/pull – To share images via registries like Docker Hub

Docker Architecture Overview:

• Docker Client: Where you type commands (docker run, docker build)
• Docker Host: Runs the Docker daemon, manages containers, images, networks, volumes
• Registry: Central repository (like Docker Hub) to store and share images

⚠️ When Not to Use Docker

• Monolithic Applications: Harder to manage if not designed for modularity
• High-Performance Needs: Some overhead due to abstraction layer
• Security-Critical Systems: Containers are less isolated than VMs (unless hardened)

💾 Data Management in Docker

• Volumes: Preferred method for persisting data outside a container’s lifecycle
• Bind Mounts: Mount a file or directory from the host machine into a container
• tmpfs Mounts: Store data only in memory (not persisted)

🔌 Networking in Docker

• Containers communicate through networks
• Docker supports:
  • Default networks
  • Custom bridge networks
  • Overlay networks (for multi-host setups)

🧩 Extensibility with Plugins

• Docker supports plugins for:
  • Storage drivers (e.g., connect to AWS S3 or Azure Blob Storage)
  • Network drivers
  • Authorization plugins

📌 Quick Recap Table

🐳 Docker CLI Cheat Sheet

🛠️ Image Management

▶️ Container Management

🔍 General Info & Troubleshooting

💡 Bonus: IBM Cloud Container Registry Commands

Make sure you’re logged in with ibmcloud login first.

🧠 Environment Variables

📦 Git Integration

✅ Quick Tip: Clean Up Unused Resources

# Stop and remove all containers
docker stop $(docker ps -aq)
docker rm $(docker ps -aq)

# Remove all unused images, networks, and build caches
docker system prune -a

📘 Glossary: Container Basics

📌 Summary Table