Docker

 

Basics of Docker

1. What is Docker, and what problems does it solve?
2. Explain the difference between a Docker container and a virtual machine.
3. What is Docker Hub, and how is it used?
4. How does Docker handle containerization?
5. What are the key components of Docker architecture?
6. Describe the role of a Dockerfile.
7. How do you create a Docker image from a Dockerfile?
8. What is the purpose of the docker run command?
9. How do you list all running Docker containers?
10. Explain the difference between docker ps and docker ps -a.

Docker Images and Containers

11. What is the Docker image lifecycle?
12. How do you remove a Docker image?
13. What are Docker container volumes, and how do they differ from Docker container bind mounts?
14. How do you create and use Docker volumes?
15. What is the purpose of Docker tags?
16. How do you manage Docker container networking?
17. Explain how to build a Docker image using a multi-stage build.
18. How do you inspect the contents of a Docker image?
19. What is the difference between COPY and ADD in a Dockerfile?
20. How do you update an existing Docker image?

Docker Networking

21. What are the different Docker network types (bridge, host, overlay)?
22. How do you create a custom Docker network?
23. Explain the concept of Docker network aliases.
24. How do you troubleshoot network issues within Docker containers?
25. What is the role of Docker Compose in managing multi-container applications?
26. How do you connect Docker containers to an external network?
27. What are Docker network drivers, and how do they work?
28. How do you use Docker networking to link containers?
29. Explain the concept of network isolation in Docker.
30. How do you expose Docker container ports to the host system?

Docker Compose

31. What is Docker Compose, and why is it used?
32. How do you define services in a docker-compose.yml file?
33. What are the key components of a docker-compose.yml file?
34. How do you scale services using Docker Compose?
35. How do you manage environment variables with Docker Compose?
36. Explain how to use Docker Compose for a development environment.
37. What is the purpose of the docker-compose up command?
38. How do you define build contexts in Docker Compose?
39. What are Docker Compose overrides, and how do you use them?
40. How do you use Docker Compose to manage persistent data?

Docker Swarm and Kubernetes

41. What is Docker Swarm, and how does it compare to Kubernetes?
42. How do you initialize a Docker Swarm cluster?
43. Explain the role of a Docker Swarm manager and worker node.
44. What are Docker Swarm services, and how do you create them?
45. How do you update a Docker Swarm service?
46. What is the purpose of Docker Swarm stack files?
47. Describe how Docker Swarm handles service scaling and load balancing.
48. How do you perform a rolling update in Docker Swarm?
49. What is Kubernetes, and how does it relate to Docker?
50. How do you deploy a Docker container to a Kubernetes cluster?

Docker Security

51. What are best practices for securing Docker containers?
52. How do you manage Docker container secrets and environment variables securely?
53. What is Docker Content Trust, and how is it used?
54. Explain the role of Docker security scanning tools.
55. How do you use Docker Bench for Security?
56. What are some common vulnerabilities in Docker containers?
57. How do you harden Docker daemon configurations?
58. What is the principle of least privilege in Docker container security?
59. How do you secure Docker images?
60. What is the purpose of Docker’s user namespace support?

Docker Performance and Optimization

61. How do you optimize Docker image build times?
62. What are Docker image layers, and how do they impact performance?
63. How do you reduce the size of Docker images?
64. What is Docker’s storage driver, and how does it affect performance?
65. How do you monitor Docker container performance?
66. What tools can you use to analyze Docker container performance?
67. How do you troubleshoot Docker container performance issues?
68. What are the best practices for optimizing Docker container startup times?
69. How do you manage and clean up unused Docker images and containers?
70. What are the implications of using different Docker storage drivers?

Advanced Docker Usage

71. How do you handle logging in Docker containers?
72. What is Docker Healthcheck, and how do you use it?
73. How do you integrate Docker with CI/CD pipelines?
74. Explain the concept of Docker container orchestration.
75. How do you use Docker for building and testing applications?
76. What is Docker Machine, and how is it used?
77. How do you manage Docker container lifecycle events?
78. What are Docker plugins, and how can they be used?
79. How do you use Docker for local development environments?
80. What is the role of Docker Daemon, and how do you configure it?

Troubleshooting and Maintenance

81. How do you diagnose and fix issues with Docker containers?
82. What steps do you take to recover from a Docker container crash?
83. How do you perform a system-wide Docker cleanup?
84. How do you handle Docker container logs?
85. What is Docker’s approach to backup and restore operations?
86. How do you troubleshoot Docker networking issues?
87. What are common Docker errors, and how do you resolve them?
88. How do you update Docker to a new version?
89. What are Docker’s health check mechanisms, and how do they work?
90. How do you handle Docker container data persistence?

Real-World Scenarios

91. Can you describe a situation where Docker significantly improved a project?
92. How do you handle multi-environment deployments using Docker?
93. What challenges have you faced with Docker in production, and how did you overcome them?
94. How do you approach Dockerizing legacy applications?
95. Explain a scenario where you had to optimize Docker container performance.
96. What strategies do you use for managing Docker in a large-scale environment?
97. How do you manage Docker container dependencies?
98. Describe a situation where Docker Compose was particularly useful.
99. How do you handle Docker container security updates in production?
100. What are your best practices for Docker image versioning and tagging?

1. What is Docker, and what problems does it solve?

Docker is an open-source platform for automating the deployment, scaling, and management of applications in lightweight containers. It solves problems like environment inconsistency across different systems, dependency management, and isolation between different services running on the same machine. Docker enables applications to run reliably across various environments.

2. Explain the difference between a Docker container and a virtual machine.

A Docker container is a lightweight, standalone package that contains everything an application needs to run (code, runtime, libraries, etc.) but shares the OS kernel with other containers. It runs in isolation but is more efficient because of this shared kernel. A Virtual Machine (VM), on the other hand, includes an entire OS, which leads to higher resource consumption and slower performance compared to containers.

3. What is Docker Hub, and how is it used?

Docker Hub is a cloud-based repository for storing and sharing Docker images. It allows users to upload images, share them with others, or pull pre-built images from the community or official repositories. Docker Hub simplifies the process of distributing and managing Docker images.

4. How does Docker handle containerization?

Docker uses the Linux kernel's cgroups and namespaces to isolate resources between containers. This makes each container feel like it is running on a separate machine, even though all containers share the same OS kernel.

5. What are the key components of Docker architecture?

• Docker Daemon: The server that manages Docker containers.

• Docker CLI: The command-line interface for interacting with the Docker daemon.

• Docker Images: The blueprints for creating containers.

• Docker Containers: The running instances of Docker images.

• Docker Hub/Registry: The storage locations for Docker images.

6. Describe the role of a Dockerfile.

A Dockerfile is a script that contains instructions for building a Docker image. It specifies the base image, dependencies, environment variables, and commands needed to configure the container.

7. How do you create a Docker image from a Dockerfile?

To create a Docker image from a Dockerfile, use the following command:

docker build -t <image-name> .

This command reads the instructions in the Dockerfile and builds an image accordingly.

8. What is the purpose of the docker run command?

The docker run command is used to create and start a new container from a specified Docker image. It can also pass environment variables, map ports, and set other options to configure the container.

9. How do you list all running Docker containers?

To list all running Docker containers, use:

docker ps

10. Explain the difference between docker ps and docker ps -a.

• docker ps: Lists only running containers.

• docker ps -a: Lists all containers, including stopped ones.

11. What is the Docker image lifecycle?

A Docker image goes through several stages:

• Build: The image is created from a Dockerfile.

• Tagging: The image is tagged with a name and version.

• Pushing: The image is pushed to a registry (like Docker Hub).

• Pulling: The image is pulled from the registry to a machine.

• Running: The image is used to create containers.

12. How do you remove a Docker image?

Use the command:

docker rmi <image-name>

13. What are Docker container volumes, and how do they differ from Docker container bind mounts?

• Volumes: Managed by Docker, these are storage units stored in a special location on the host filesystem.

• Bind Mounts: Link to a specific location on the host filesystem, and the host and container both access the same files.

14. How do you create and use Docker volumes?

To create a volume:

docker volume create <volume-name>

To use it in a container:

docker run -v <volume-name>:<container-path> <image-name>

15. What is the purpose of Docker tags?

Docker tags are used to label versions of images, making it easy to manage different versions. For example, my-image:v1 can be used to tag version 1 of the image.

16. How do you manage Docker container networking?

Docker allows you to define container networking via different drivers (e.g., bridge, host, overlay). Containers can communicate with each other through networks, and users can expose specific ports on containers to the host.

17. Explain how to build a Docker image using a multi-stage build.

A multi-stage build allows you to use multiple FROM statements in a Dockerfile to create smaller, more efficient images. This helps in separating the build environment from the runtime environment.

18. How do you inspect the contents of a Docker image?

To inspect a Docker image:

docker inspect <image-name>

19. What is the difference between COPY and ADD in a Dockerfile?

• COPY: Copies files from the local filesystem into the container.

• ADD: Similar to COPY, but also supports remote URLs and extracting tar files.

20. How do you update an existing Docker image?

To update a Docker image:

1. Modify the Dockerfile.

2. Rebuild the image using docker build -t <image-name> .

3. Optionally, push the new image to the registr

21. What are the different Docker network types (bridge, host, overlay)?

• Bridge: The default network driver for standalone containers, where containers are isolated.

• Host: Shares the host’s network namespace, meaning the container uses the host’s IP address.

• Overlay: Used for multi-host networking in Docker Swarm or Kubernetes, allowing containers to communicate across different hosts.

22. How do you create a custom Docker network?

docker network create <network-name>

23. Explain the concept of Docker network aliases.

Aliases allow you to reference containers by a name or alias within the same network. This makes it easier to communicate between containers.

24. How do you troubleshoot network issues within Docker containers?

You can use the docker network inspect <network-name> command to inspect the network configuration, and check logs and connectivity issues between containers using docker logs and ping.

25. What is the role of Docker Compose in managing multi-container applications?

Docker Compose simplifies the management of multi-container applications by defining them in a docker-compose.yml file. It automates the creation, scaling, and linking of multiple containers.

26. How do you connect Docker containers to an external network?

You can connect a Docker container to an external network using:

docker network connect <network-name> <container-name>

27. What are Docker network drivers, and how do they work?

Network drivers are the different types of networks that Docker can use to connect containers, such as bridge, host, and overlay.

28. How do you use Docker networking to link containers?

Containers can be linked by specifying the --link option during docker run, but it’s recommended to use user-defined networks instead, which allow containers to reference each other by name.

29. Explain the concept of network isolation in Docker.

Docker isolates containers from each other and from the host by default. Containers on the same network can communicate with each other, while containers on different networks cannot unless explicitly connected.

30. How do you expose Docker container ports to the host system?

You expose container ports using the -p flag:

docker run -p <host-port>:<container-port> <image-name>

31. What is Docker Compose, and why is it used?

Docker Compose is a tool to define and manage multi-container applications. It uses a docker-compose.yml file to configure services, networks, and volumes for a set of containers.

32. How do you define services in a docker-compose.yml file?

A service is defined in the docker-compose.yml file with a name and a Docker image:

services:
  web:
    image: nginx

33. What are the key components of a docker-compose.yml file?

Key components include:

• services: Defines the containers and their configurations.

• networks: Defines networks for communication between services.

• volumes: Defines shared storage for services.

34. How do you scale services using Docker Compose?

To scale a service, use the --scale option:

docker-compose up --scale <service-name>=<num-instances>

35. How do you manage environment variables with Docker Compose?

You can define environment variables in the docker-compose.yml file under the environment section or in a .env file.

36. Explain how to use Docker Compose for a development environment.

You can use Docker Compose to create isolated development environments, specifying all dependencies (databases, caches) in the docker-compose.yml file.

37. What is the purpose of the docker-compose up command?

docker-compose up creates and starts the containers defined in a docker-compose.yml file.

38. How do you define build contexts in Docker Compose?

Build contexts are defined by specifying a build section in the docker-compose.yml file:

services:
  app:
    build: .

39. What are Docker Compose overrides, and how do you use them?

Overrides allow you to specify different configurations for different environments (e.g., docker-compose.override.yml for development).

40. How do you use Docker Compose to manage persistent data?

You can define volumes in the docker-compose.yml file to store data persistently across container restarts.

41. What is Docker Swarm, and how does it compare to Kubernetes?

Docker Swarm is Docker’s native clustering and orchestration tool, designed to manage a group of Docker hosts as a single virtual system. It provides simple scaling and load balancing. Kubernetes, on the other hand, is a more complex orchestration platform with advanced features for automated deployment, scaling, and management of containerized applications across multiple hosts.

42. How do you initialize a Docker Swarm cluster?

To initialize a Docker Swarm cluster, run:

docker swarm init

43. Explain the role of a Docker Swarm manager and worker node.

• Manager Node: Manages the swarm, schedules tasks, and distributes workloads to worker nodes.

• Worker Node: Executes tasks assigned by the manager node (i.e., runs containers).

44. What are Docker Swarm services, and how do you create them?

A Swarm service is a task or container deployed on a Swarm cluster. You create a service with:

docker service create --name <service-name> <image-name>

45. How do you update a Docker Swarm service?

To update a Docker Swarm service:

docker service update <service-name>

46. What is the purpose of Docker Swarm stack files?

A stack file is used to define and deploy a collection of services in a Swarm cluster, using docker-compose.yml format. You can deploy it using:

docker stack deploy -c <stack-file> <stack-name>

47. Describe how Docker Swarm handles service scaling and load balancing.

Docker Swarm automatically handles load balancing by distributing incoming requests across the available containers in a service. Scaling is as simple as increasing or decreasing the number of replicas with:

docker service scale <service-name>=<num-replicas>

48. How do you perform a rolling update in Docker Swarm?

To perform a rolling update, use:

docker service update --update-parallelism <N> <service-name>

This updates containers in batches to avoid downtime.

49. What is Kubernetes, and how does it relate to Docker?

Kubernetes is an open-source platform for automating the deployment, scaling, and management of containerized applications. It works with Docker (and other container runtimes) to manage containers at scale. Kubernetes provides advanced features like service discovery, automated scaling, and orchestration.

50. How do you deploy a Docker container to a Kubernetes cluster?

To deploy a Docker container to Kubernetes:

1. Create a Kubernetes Deployment configuration (usually in YAML format).

2. Use kubectl apply -f <deployment-file>.yaml to deploy it.

51. What are best practices for securing Docker containers?

Best practices include:

• Use official images or well-maintained ones.

• Keep the Docker daemon updated.

• Implement least privilege principles.

• Run containers with non-root users.

• Scan images for vulnerabilities.

52. How do you manage Docker container secrets and environment variables securely?

Use Docker’s secret management feature for storing sensitive data like passwords. For environment variables, avoid hardcoding them into images and use external configurations or encrypted secrets.

53. What is Docker Content Trust, and how is it used?

Docker Content Trust (DCT) ensures that only signed images are pulled from Docker Hub. This helps prevent malicious code from running. It can be enabled using:

export DOCKER_CONTENT_TRUST=1

54. Explain the role of Docker security scanning tools.

Docker security scanning tools scan images for known vulnerabilities. Docker Hub includes an integrated security scanning feature that identifies issues in base images.

55. How do you use Docker Bench for Security?

Docker Bench for Security is a script that checks for security best practices in Docker installations. You can run it with:

docker run -it --net host --privileged --pid host --userns host --cap-add audit_control \
  --volume /var/lib/docker:/var/lib/docker:ro \
  --volume /var/run/docker.sock:/var/run/docker.sock:ro \
  --volume /etc:/etc:ro \
  docker/docker-bench-security

56. What are some common vulnerabilities in Docker containers?

Common vulnerabilities include:

• Running containers as root.

• Outdated base images.

• Exposed sensitive information in environment variables.

• Unnecessary services running inside containers.

57. How do you harden Docker daemon configurations?

Hardening Docker configurations involves:

• Using user namespaces for container isolation.

• Limiting Docker daemon exposure to trusted users.

• Enabling AppArmor or SELinux for security policies.

58. What is the principle of least privilege in Docker container security?

The principle of least privilege suggests that containers should run with only the necessary permissions required to perform their task, reducing potential damage in case of a compromise.

59. How do you secure Docker images?

Secure Docker images by:

• Using official images.

• Minimizing image layers.

• Regularly scanning for vulnerabilities.

• Avoiding unnecessary software or packages in the image.

60. What is the purpose of Docker’s user namespace support?

Docker's user namespaces feature allows you to map the root user in a container to a non-root user on the host, which reduces the risk of privilege escalation.

61. How do you optimize Docker image build times?

To optimize build times:

• Use multi-stage builds.

• Cache layers that don’t change frequently.

• Minimize the number of layers in the image.

62. What are Docker image layers, and how do they impact performance?

Docker images are made up of layers, where each layer represents a modification or addition. Layers improve performance by allowing Docker to cache unchanged parts of an image, but excessive layers can increase the image size.

63. How do you reduce the size of Docker images?

You can reduce image size by:

• Using slim base images (e.g., alpine).

• Removing unnecessary dependencies.

• Combining RUN commands in the Dockerfile.

64. What is Docker’s storage driver, and how does it affect performance?

A storage driver is responsible for managing container filesystem storage. Different storage drivers (e.g., aufs, overlay2) have different performance characteristics depending on the workload.

65. How do you monitor Docker container performance?

You can monitor Docker container performance using:

• docker stats: Shows resource usage (CPU, memory, etc.).

• Third-party tools like Prometheus and Grafana.

66. What tools can you use to analyze Docker container performance?

Tools like cAdvisor, Prometheus, and Datadog help in analyzing Docker container performance.

67. How do you troubleshoot Docker container performance issues?

Use docker stats to check the resource usage and docker logs to examine container logs. Additionally, use external monitoring tools to pinpoint performance bottlenecks.

68. What are the best practices for optimizing Docker container startup times?

Optimize Docker container startup times by:

• Minimizing the number of processes inside containers.

• Avoiding heavy initialization tasks on container start.

69. How do you manage and clean up unused Docker images and containers?

To clean up unused containers and images, use:

docker system prune

70. What are the implications of using different Docker storage drivers?

Different storage drivers impact performance, compatibility, and stability. For example, overlay2 is generally faster and more efficient than aufs.

 

71. How do you handle logging in Docker containers?

Docker containers log their output to stdout and stderr, which can be accessed with docker logs <container-id>. You can also configure logging drivers (e.g., fluentd, syslog, json-file) to send logs to external systems.

72. What is Docker Healthcheck, and how do you use it?

A Healthcheck is used to determine whether a container is functioning properly. You can define a health check in the Dockerfile using the HEALTHCHECK instruction. For example:

HEALTHCHECK CMD curl --fail http://localhost:8080 || exit 1

73. How do you integrate Docker with CI/CD pipelines?

Docker integrates with CI/CD tools (like Jenkins, GitLab CI, CircleCI) to automate the process of building, testing, and deploying containerized applications. The general workflow involves building a Docker image, running tests, and pushing the image to a registry.

74. Explain the concept of Docker container orchestration.

Orchestration refers to the automated management of containerized applications, including deployment, scaling, and networking. Docker Swarm and Kubernetes are the two main orchestration tools for managing containerized environments.

75. How do you use Docker for building and testing applications?

Docker allows you to create isolated environments to build and test applications. You can define dependencies in a Dockerfile, build an image, and then run tests inside containers to ensure consistency across environments.

76. What is Docker Machine, and how is it used?

Docker Machine is a tool for provisioning Docker hosts on various platforms (e.g., local VMs, cloud providers). It helps in creating, managing, and interacting with remote Docker hosts.

77. How do you manage Docker container lifecycle events?

You manage Docker container lifecycle events using Docker commands such as:

• docker run: Start a container.

• docker stop: Stop a running container.

• docker restart: Restart a container.

• docker rm: Remove a stopped container.

78. What are Docker plugins, and how can they be used?

Docker plugins extend Docker’s functionality, such as adding storage drivers, networking drivers, or logging drivers. They can be installed via the Docker CLI and can be used for specialized container management.

79. How do you use Docker for local development environments?

Docker can be used for local development by creating containerized environments that match the production environment, allowing developers to work in isolated environments with consistent configurations.

80. What is the role of Docker Daemon, and how do you configure it?

The Docker Daemon (dockerd) is responsible for managing Docker containers, images, networks, and volumes. You can configure it by modifying the Docker daemon configuration file (/etc/docker/daemon.json) or by passing flags when starting the daemon.

81. How do you diagnose and fix issues with Docker containers?

Diagnosing issues involves:

• Checking the container logs with docker logs <container-id>.

• Inspecting the container’s status with docker inspect <container-id>.

• Checking resource usage with docker stats.

82. What steps do you take to recover from a Docker container crash?

• Check the container logs with docker logs.

• Inspect the container's exit code with docker inspect <container-id>.

• Restart the container using docker restart.

83. How do you perform a system-wide Docker cleanup?

You can clean up unused containers, images, volumes, and networks using:

docker system prune

You can also specify options like --volumes to include unused volumes.

84. How do you handle Docker container logs?

Docker container logs can be accessed with docker logs <container-id>. For long-term logging, configure a logging driver like fluentd, syslog, or json-file to send logs to a central location.

85. What is Docker’s approach to backup and restore operations?

For container data, Docker recommends using volumes to persist data. You can back up volumes by creating a copy of the data and restore by copying it back. For images, you can use docker save to back up and docker load to restore.

86. How do you troubleshoot Docker networking issues?

Troubleshoot networking issues by:

• Inspecting network settings with docker network inspect <network-name>.

• Checking container logs for network-related errors.

• Using ping and docker exec to test connectivity between containers.

87. What are common Docker errors, and how do you resolve them?

Common errors include:

• Container crashes: Check logs and inspect for application-level issues.

• Port conflicts: Ensure ports aren’t already in use on the host system.

• Image pull errors: Check internet connectivity and ensure the image exists.

88. How do you update Docker to a new version?

To update Docker:

1. For Ubuntu/Debian: sudo apt-get update && sudo apt-get install docker-ce

2. For CentOS/RHEL: sudo yum update docker-ce

3. For Windows/macOS: Update through Docker Desktop.

89. What are Docker’s health check mechanisms, and how do they work?

Docker uses health checks to monitor the status of a container. You can define the health check in the Dockerfile with the HEALTHCHECK instruction. Docker periodically checks the container’s health and marks it as unhealthy if it fails.

90. How do you handle Docker container data persistence?

To ensure data persistence, use Docker volumes. Volumes store data outside the container filesystem, allowing it to persist even after a container is stopped or removed. Use the -v option to mount volumes.

91. Can you describe a situation where Docker significantly improved a project?

Docker can improve a project by providing consistent environments across development, testing, and production. For example, when a project faced issues with “works on my machine” syndrome, Docker was used to standardize the environment, reducing configuration issues.

92. How do you handle multi-environment deployments using Docker?

Multi-environment deployments can be managed by creating different docker-compose.yml files or using Docker Compose overrides to specify environment-specific configurations (e.g., development, staging, production).

93. What challenges have you faced with Docker in production, and how did you overcome them?

Challenges include managing storage and networking between containers. These were overcome by using Docker volumes and orchestrating containers with Docker Swarm to handle scaling and networking automatically.

94. How do you approach Dockerizing legacy applications?

Dockerizing legacy applications involves creating a Dockerfile that defines the necessary environment, dependencies, and configurations. It’s important to test thoroughly and gradually migrate legacy services to containers.

95. Explain a scenario where you had to optimize Docker container performance.

To optimize Docker container performance, we reduced image sizes, used a multi-stage build for more efficient images, and optimized the application to run more efficiently within containers by adjusting resource limits.

96. What strategies do you use for managing Docker in a large-scale environment?

For large-scale environments, Docker is typically managed with Docker Swarm or Kubernetes. You would also use tools like Prometheus for monitoring and Helm for managing Kubernetes charts.

97. How do you manage Docker container dependencies?

Dependencies are managed through Docker images and Docker Compose configurations. With Docker Compose, you define services in a docker-compose.yml file, ensuring all containers are correctly linked and dependencies are met.

98. Describe a situation where Docker Compose was particularly useful.

Docker Compose was used for setting up a development environment with multiple services (e.g., a web app, database, cache) running in different containers. This streamlined the setup process and made the development workflow more efficient.

99. How do you handle Docker container security updates in production?

Security updates are handled by regularly scanning Docker images for vulnerabilities, applying updates to base images, and redeploying the affected containers. Automated CI/CD pipelines help ensure containers are always up to date.

100. What are your best practices for Docker image versioning and tagging?

Best practices include using semantic versioning for tagging images, such as v1.0, v1.1, and using latest only for development purposes. Also, using descriptive tags (e.g., myapp:v1.0 and myapp:v2.0) makes it easier to manage image versions.