Docker Certified Associate (DCA)

Installation and Configuration of Docker Engine

Understanding Docker Engine Architecture and Components

• Gaining a deep understanding of the Docker daemon, Docker client, Docker registries, and Docker objects (images, containers, networks, volumes).
• Understanding how the Docker client communicates with the Docker daemon via REST API.
• Examining the storage drivers used by Docker, such as `overlay2`, `aufs`, and `devicemapper`, and their implications for performance and disk usage.

Installing and Upgrading Docker Engine

• Mastering the installation process for Docker Engine on various Linux distributions like Ubuntu, CentOS, and Fedora, including repository configuration.
• Understanding the steps for installing Docker Engine on Windows Server and configuring it for containerization.
• Learning how to perform in-place upgrades of the Docker Engine, understanding version compatibility and potential impacts.
• Installing Docker Engine without internet access using pre-downloaded `.deb` or `.rpm` packages, managing dependencies manually.

Configuring the Docker Daemon

• Configuring the Docker daemon using the `daemon.json` file for various settings such as logging drivers, default network configurations, and experimental features.
• Setting up logging for containers, including `json-file`, `syslog`, `journald`, `gelf`, and `fluentd` drivers, with specific options like log rotation and size limits.
• Managing the Docker daemon as a systemd service, including starting, stopping, restarting, and enabling/disabling it at boot.
• Adjusting Docker daemon settings to enable specific features, such as user namespaces for enhanced security or setting default `ulimits` for containers.
• Configuring proxy settings for the Docker daemon to allow image pulls from external registries in restricted network environments.

Image Creation, Management, and Registry

Designing and Building Docker Images

• Mastering Dockerfile best practices for creating efficient, secure, and small images, including multi-stage builds.
• Utilizing key Dockerfile instructions: `FROM`, `RUN`, `CMD`, `ENTRYPOINT`, `COPY`, `ADD`, `EXPOSE`, `VOLUME`, `WORKDIR`, `ARG`, `ENV`, `LABEL`, `HEALTHCHECK`, and `USER`.
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• Implementing multi-stage builds to separate build-time dependencies from runtime environments, significantly reducing final image size. For example, compiling a Go application in a `builder` stage and copying only the compiled binary to a minimal `scratch` or `alpine` image.
• Understanding the concept of image layers and how they impact image size, build caching, and security.
• Optimizing Dockerfiles for build cache utilization, ensuring faster rebuilds when only specific layers change.

Managing Docker Images

• Tagging images effectively for versioning, release management, and differentiating build stages (e.g., `latest`, `v1.0`, `dev`).
• Inspecting image metadata using `docker inspect` to understand layers, configurations, and environment variables.
• Cleaning up unused or dangling images to reclaim disk space, distinguishing between `docker rmi` and `docker image prune`.
• Understanding and utilizing image manifest lists for multi-architecture images.

Working with Docker Registries

• Pulling images from public registries like Docker Hub and private registries.
• Pushing custom-built images to both public and private Docker registries, including authentication mechanisms.
• Configuring client-side Docker to authenticate with various private registries using `docker login` and credential helpers.
• Understanding the role of content trust and image signing for verifying image integrity and authenticity when pulling from registries.

Container Orchestration with Docker Swarm

Understanding Docker Swarm Architecture

• Gaining a comprehensive understanding of Swarm mode concepts: managers, worker nodes, services, tasks, replicas, and load balancing.
• Differentiating between manager and worker node responsibilities and understanding the quorum mechanism for manager node high availability.
• Understanding the Raft consensus algorithm used by Swarm managers for state consistency.

Deploying and Managing Services

• Initializing a Docker Swarm cluster across multiple nodes and joining new nodes as managers or workers.
• Deploying services with specific replica counts, port mappings, and resource constraints (CPU/memory limits and reservations). For instance, deploying an `nginx` web server service with three replicas and limiting each replica to 0.5 CPU cores and 256MB memory.
• Scaling services up and down dynamically using `docker service scale` or `docker service update`.
• Performing rolling updates for services to deploy new image versions or configuration changes without downtime. For example, updating an `nginx` service from `nginx:1.20` to `nginx:1.21` with a specific update delay and parallelism.
• Rolling back service updates in case of issues to a previous working version.
• Configuring service placement constraints and preferences to control where service tasks run within the Swarm.
• Managing service networks and connecting services to custom overlay networks for inter-service communication.

Node and Cluster Management

• Draining nodes to gracefully remove tasks and prepare for maintenance without impacting service availability.
• Pausing or resuming a node’s ability to accept new tasks.
• Promoting worker nodes to managers and demoting managers to workers.
• Removing nodes from a Swarm cluster.
• Understanding and managing Swarm ingress routing mesh for external access to services.

Secrets and Configurations Management

• Creating and managing Docker secrets for sensitive data like database credentials or API keys.
• Mounting secrets into services securely as files or environment variables within containers. For example, creating a secret for a database password and mounting it into a `web-app` service at `/run/secrets/db_password`.
• Creating and managing Docker configurations for non-sensitive configuration files, such as `nginx.conf` or application settings.
• Updating secrets and configurations, understanding how changes are propagated to running services.

Networking in Docker

Understanding Docker Network Drivers

• Deeply understanding the default Docker network drivers: `bridge`, `host`, `none`, and `overlay`.
• Exploring advanced network drivers like `macvlan` for assigning MAC and IP addresses to containers from a physical network.
• Understanding the use cases and implications of each network driver for container communication and isolation.

Configuring and Managing Networks

• Creating and managing custom bridge networks for single-host container communication and isolation.
• Connecting containers to multiple custom bridge networks, enabling multi-homed containers.
• Configuring port publishing for containers, mapping container ports to host ports using `docker run -p`. Understanding the differences between host-port binding and publishing to the routing mesh in Swarm.
• Creating and managing overlay networks for multi-host container communication within a Docker Swarm.
• Inspecting network configurations using `docker network inspect` to view connected containers, IP addresses, and driver details.

Service Discovery and DNS

• Understanding Docker's embedded DNS for service discovery within custom networks and Swarm overlay networks.
• Configuring external DNS servers for containers or services.
• Troubleshooting common Docker networking issues, such as port conflicts, network isolation problems, and DNS resolution failures.

Storage and Volumes in Docker

Understanding Data Persistence Mechanisms

• Mastering the differences and use cases for Docker volumes, bind mounts, and `tmpfs` mounts.
• Understanding when to use each storage type for data persistence, development workflows, or ephemeral data.

Managing Docker Volumes

• Creating, listing, inspecting, and removing Docker volumes using `docker volume` commands. For example, creating a named volume `mydata` for a database container to persist its data.
• Attaching volumes to containers at specified mount points, ensuring data remains available even if the container is removed.
• Understanding volume drivers and their role in integrating Docker with external storage solutions.
• Cleaning up unused or dangling volumes to free up disk space.

Using Bind Mounts and tmpfs Mounts

• Utilizing bind mounts for development purposes, mounting host directories directly into containers for live code changes. For example, mounting a local source code directory `/src` into a container at `/app`.
• Understanding the security implications and performance characteristics of bind mounts compared to volumes.
• Implementing `tmpfs` mounts for ephemeral, non-persistent data that resides only in the host's memory, such as temporary cache files.

Docker Security

Securing the Docker Daemon and Host

• Implementing TLS to secure the Docker daemon API, ensuring encrypted communication between the client and daemon.
• Configuring client-side TLS certificates for authenticated access to the Docker daemon.
• Understanding the principle of least privilege for the Docker daemon, including running it as a non-root user when possible.
• Securing the Docker host operating system by following best practices, such as regularly patching, limiting open ports, and configuring firewalls.

Container Security Best Practices

• Running containers with minimal privileges, using non-root users and understanding the implications of the `--user` flag in Dockerfiles and `docker run`.
• Limiting container capabilities using `cap-drop` and `cap-add` to restrict actions a container can perform on the host kernel. For example, dropping `NET_RAW` to prevent raw socket access.
• Understanding the concept of the read-only root filesystem and implementing it with `--read-only` to prevent writes to the container's root.
• Setting resource constraints for containers using `--cpu-shares`, `--cpus`, `--memory`, and `--memory-swap` to prevent resource exhaustion attacks.
• Implementing `HEALTHCHECK` instructions in Dockerfiles to ensure applications inside containers are genuinely healthy, not just running.

Image Security and Content Trust

• Enabling Docker Content Trust (DCT) to verify the authenticity and integrity of images during pull operations through digital signatures.
• Signing Docker images using Notary for trusted image distribution.
• Understanding the importance of regularly scanning images for known vulnerabilities using security tools.
• Minimizing the attack surface by creating small, lean images using multi-stage builds and minimal base images (e.g., `alpine`, `scratch`).
• Avoiding the use of `ADD` in Dockerfiles where `COPY` is sufficient, to prevent unexpected archive extraction and URL download behaviors.

Advanced Security Concepts

• Understanding the role of Linux kernel security features like AppArmor and SELinux in enhancing container isolation.
• Implementing Docker secrets for managing sensitive information securely within Swarm services, preventing credentials from being exposed in environment variables or configuration files.
• Utilizing user namespaces to remap root user inside a container to a non-root user on the host, adding another layer of isolation.