# Unit 5: Introduction to Docker and Deep Dive into Docker Tools --- ## 1. Business Problems, Goals, and Requirements ### 1.1 Business Problems & Goals * **Problem:** Challenges faced by a business (e.g., slow deployment, inconsistent environments, scaling issues). * **Goals:** Desired outcomes to solve problems (e.g., faster time-to-market, improved reliability, cost reduction). * **Exam Point:** Understanding the 'why' behind application development, linking technical solutions to business objectives. ### 1.2 Functional & Non-Functional Requirements * **Functional Requirements:** What the system *does* (e.g., user authentication, data processing). * **Non-Functional Requirements (NFRs):** How the system *performs* (e.g., **performance**, **scalability**, **security**, **availability**, **maintainability**). * **Exam Point:** NFRs are critical for cloud-native applications; Docker and Kubernetes directly address many NFRs like scalability and portability. ### 1.3 IBM Cloud Services * **App ID:** Identity and Access Management (IAM) service for securing cloud applications. * **Key Features:** Authentication, authorization, user management. * **Watson Services:** AI and machine learning services. * **Examples:** Natural Language Understanding, Speech to Text, Visual Recognition. * **Exam Point:** These services can be integrated into cloud applications to add advanced functionalities and security. --- ## 2. Introduction to Docker ### 2.1 What is Docker? * **Docker:** An open-source platform for developing, shipping, and running applications in **containers**. * **Container:** A lightweight, standalone, executable package of software that includes everything needed to run it: code, runtime, system tools, system libraries, and settings. * **Exam Point:** Docker standardizes application packaging and deployment. ### 2.2 Benefits of Using Docker for Cloud Applications * **Consistency:** **"It works on my machine"** problem solved. Identical environments across development, testing, and production. * **Portability:** Applications can run anywhere Docker is installed (local, on-prem, any cloud). * **Isolation:** Containers are isolated from each other and the host OS. * **Resource Efficiency:** Lighter than VMs, faster startup times, less overhead. * **Scalability:** Easy to spin up multiple instances of an application. * **Faster Deployment:** Streamlined build and deployment pipelines. * **Exam Point:** Docker significantly improves the efficiency and reliability of cloud application development and deployment lifecycle. ### 2.3 Docker Engine * The core component of Docker. * **Components:** * **Docker Daemon (dockerd):** A background service that manages Docker objects (images, containers, networks, volumes). * **Docker CLI (docker):** A command-line client used to interact with the daemon. * **Exam Point:** Understanding the client-server architecture of Docker. ### 2.4 Docker Images * A **read-only template** used to create containers. * Contains the application code, libraries, dependencies, and configuration. * Built from a `Dockerfile`. * **Exam Point:** Images are the blueprints for containers. ### 2.5 Docker Containers * A **runnable instance** of a Docker image. * A running process with its own filesystem, processes, and network interface, isolated from the host. * **Exam Point:** Containers are the actual running applications. ### 2.6 Docker Registries * A **repository** for storing and distributing Docker images. * **Public Registries:** Docker Hub (default). * **Private Registries:** For proprietary images (e.g., IBM Cloud Container Registry, Docker Trusted Registry). * **Exam Point:** Registries are essential for sharing and managing Docker images. --- ## 3. Docker CLI vs. Docker Compose ### 3.1 Docker CLI * **`docker` command:** Used for managing individual containers, images, networks, and volumes. * **Examples:** `docker run`, `docker build`, `docker ps`, `docker stop`, `docker rm`. * **Use Case:** Managing single containers or simple multi-container applications. ### 3.2 Docker Compose * A **tool for defining and running multi-container Docker applications**. * Uses a YAML file (`docker-compose.yml`) to configure application services, networks, and volumes. * **Commands:** `docker-compose up`, `docker-compose down`, `docker-compose ps`. * **Use Case:** Orchestrating complex applications with multiple interconnected services (e.g., web server, database, cache). * **Exam Point:** Docker Compose simplifies the management of multi-container applications, crucial for microservices. --- ## 4. Writing and Managing Dockerfiles, Images, and Containers ### 4.1 Writing a Dockerfile * A text file that contains **instructions for building a Docker image**. * **Key Instructions:** * `FROM`: Specifies the base image. * `RUN`: Executes commands in a new layer on top of the current image. * `COPY`/`ADD`: Copies files into the image. * `WORKDIR`: Sets the working directory for subsequent instructions. * `EXPOSE`: Informs Docker that the container listens on specified network ports. * `CMD`/`ENTRYPOINT`: Provides defaults for an executing container. * **Exam Point:** `Dockerfile` is the recipe for creating reproducible environments. ```dockerfile # Example Dockerfile FROM ubuntu:latest LABEL maintainer="Your Name " RUN apt-get update && apt-get install -y nginx COPY ./html /var/www/html EXPOSE 80 CMD ["nginx", "-g", "daemon off;"] ``` ### 4.2 Building a Docker Image * **Command:** `docker build -t : .` * `-t`: Tag the image (name:tag). * `.`: The build context (directory containing `Dockerfile`). * **Process:** Docker reads the `Dockerfile`, executes instructions, and creates layers, forming a new image. * **Exam Point:** Building an image from a `Dockerfile` creates a portable, reproducible application artifact. ### 4.3 Running a Docker Container * **Command:** `docker run [OPTIONS] : [COMMAND] [ARG...]` * **Common Options:** * `-d`: Run container in **detached mode** (background). * `-p :`: **Publish a container's port** to the host. * `--name `: Assign a name to the container. * `-v :`: **Mount a volume** for persistent storage. * **Example:** `docker run -d -p 8080:80 --name my-nginx nginx:latest` ### 4.4 Managing Docker Containers * **List running containers:** `docker ps` * **List all containers (running and stopped):** `docker ps -a` * **Stop a container:** `docker stop ` * **Start a stopped container:** `docker start ` * **Restart a container:** `docker restart ` * **Remove a container:** `docker rm ` (must be stopped first) * **Remove all stopped containers:** `docker container prune` * **Exam Point:** Effective container management is key for application lifecycle. --- ## 5. Docker Hub and Private Registries ### 5.1 Docker Hub * A **cloud-based registry service** for storing and sharing Docker images. * Provides a vast library of pre-built images (e.g., official OS images, application stacks). * **Commands:** * `docker login`: Log in to Docker Hub. * `docker pull :`: Download an image from Docker Hub. * `docker push /:`: Upload an image to Docker Hub. * **Exam Point:** Docker Hub is the default public repository for sharing and distributing Docker images. ### 5.2 Private Registries * Used for storing **private Docker images**, typically for internal use or proprietary software. * **Benefits:** Security, control over image distribution. * **Examples:** IBM Cloud Container Registry, AWS ECR, Google GCR, self-hosted registries. * **Commands:** Similar to Docker Hub, but often requires specific authentication details. * **Exam Point:** Private registries are crucial for enterprise-level container management and security. ### 5.3 Container Registry with IBM Cloud * A **managed private Docker container registry** on IBM Cloud. * Allows users to store, manage, and secure container images privately. * Integrates with other IBM Cloud services for CI/CD pipelines. * **Exam Point:** IBM Cloud Container Registry provides a secure and scalable solution for managing private container images within the IBM Cloud ecosystem. --- ## 6. Introduction to Kubernetes ### 6.1 What is Kubernetes? * An **open-source system for automating deployment, scaling, and management of containerized applications**. * Originally designed by Google, now maintained by the Cloud Native Computing Foundation (CNCF). * Also known as **K8s**. * **Exam Point:** Kubernetes is the de facto standard for container orchestration. ### 6.2 Key Capabilities of Kubernetes * **Automated Rollouts and Rollbacks:** Manage application updates and revert to previous versions if issues arise. * **Service Discovery and Load Balancing:** Automatically expose containers to the network and distribute traffic. * **Storage Orchestration:** Mount storage systems (local, cloud providers, network storage). * **Self-Healing:** Restarts failing containers, replaces and reschedules containers when nodes die, kills containers that don't respond to health checks. * **Automatic Bin Packing:** Schedules containers onto nodes based on resource requirements and constraints. * **Secret and Configuration Management:** Deploy and update secrets and application configurations without rebuilding images. * **Exam Point:** These capabilities enable robust, resilient, and scalable containerized application deployments. ### 6.3 Kubernetes Building Blocks #### 6.3.1 Pod * The **smallest deployable unit** in Kubernetes. * Represents a single instance of a running process in a cluster. * A Pod can contain one or more **containers**, which are always co-located and co-scheduled, and share resources (networking, storage). * **Exam Point:** Pods are the fundamental units of deployment. **[Figure: Pod Structure]** This figure illustrates the components of a Kubernetes Pod, showing how containers, storage, and network resources are shared. It is important for understanding how applications are packaged and run within Kubernetes. #### 6.3.2 Deployment * An **object that describes the desired state for Pods and ReplicaSets**. * Manages the rollout of Pods and provides declarative updates. * Ensures a specified number of Pod replicas are running at all times. * **Key Features:** Rolling updates, rollback, scaling. * **Exam Point:** Deployments abstract away the complexity of managing individual Pods and provide a declarative way to manage application lifecycles. #### 6.3.3 Service * An **abstraction that defines a logical set of Pods and a policy by which to access them**. * Provides a stable IP address and DNS name for a set of Pods. * Enables **loosely coupled communication** between applications. * **Types:** ClusterIP, NodePort, LoadBalancer, ExternalName. * **Exam Point:** Services are essential for enabling reliable networking and communication between microservices in a Kubernetes cluster. **[Figure: Kubernetes Service Discovery]** This figure depicts how a Kubernetes Service routes external traffic to a set of backend Pods, abstracting their individual IP addresses. It is crucial for understanding network access and load balancing in Kubernetes. ### 6.4 Kubernetes Cluster * A **set of machines** (physical or virtual) that run containerized applications managed by Kubernetes. * **Components:** * **Control Plane (Master):** Manages the cluster state, schedules Pods, etc. * API Server, etcd, Controller Manager, Scheduler. * **Worker Nodes:** Run the actual application containers (Pods). * Kubelet, Kube-proxy, Container Runtime (e.g., Docker). * **Exam Point:** A cluster is the fundamental infrastructure for running Kubernetes. ---