Docker Interview Questions

If you are looking for Docker Interview Questions, here is the comprehensive list from basic to most advanced docker container interview questions for 2+, 3+, 4+, 5+ years of experienced professionals. These docker devops interview questions will help you to crack your devops job interview.

Docker Interview Questions

1. What is Docker?
2. What is the difference between Docker image and Docker container?
3. How will you remove an image from Docker?
4. How is a Docker container different from a hypervisor?
5. Can we write compose file in JSON file instead of YAML?
6. Can we run multiple apps on one server with Docker?
7. What are the common use cases of Docker?
8. What are the main features of Docker-compose?
9. What is the most popular use of Docker?
10. What is the role of open source development in the popularity of Docker?
11. What is the difference between Docker commands: up, run and start?
12. What is Docker Swarm?
13. What are the features of Docker Swarm?
14. What is a Docker Image?
15. What is a Docker Container?
16. What is Docker Machine?
17. Why do we use Docker Machine?
18. How will you create a Container in Docker?
19. Do you think Docker is Application-centric or Machine-centric?
20. Can we lose our data when a Docker Container exits?
21. Can we run more than one process in a Docker container?
22. What are the objects created by Docker Cloud  in Amazon Web Services (AWS) EC2?

Top Docker Interview Questions

1. How will you take a backup of Docker container volumes in AWS S3?
2. What are the three main steps of Docker Compose?
3. What is Pluggable Storage Driver architecture in Docker-based containers?
4. What is Docker Hub?
5. What are the main features of Docker Hub?
6. What are the main security concerns with Docker-based containers?
7. What are the security benefits of using Container-based system?
8. How can we check the status of a Container in Docker?
9. What are the main benefits of using Docker?
10. How does Docker simplify Software Development process?
11. What is the basic architecture behind Docker?
12. What are the popular tasks that you can do with Docker Command line tool?
13. What type of applications- Stateless or Stateful is more suitable for Docker Container?
14. How can Docker run on different Linux distributions?
15. Why do we use Docker on top of a virtual machine?
16. How can Docker container share resources?
17. What is the difference between Add and Copy command in a Dockerfile?
18. What is Docker Entrypoint?
19. What is ONBUILD command in Docker?
20. What is Build cache in Docker?
21. What are the most common instructions in Dockerfile?
22. What is the purpose of EXPOSE command in Dockerfile?
23. What are the different kinds of namespaces available in a Container?
24. How will you monitor Docker in production?
25. What are the Cloud platforms that support Docker?
26. How can we control the startup order of services in Docker compose?
27. Why Docker compose does not wait for a container to be ready before moving on to start the next service in dependency order?
28. How will you customize Docker compose file for different environments?

Docker Interview Questions and Answers

1. So what exactly is Docker? Something about “container applications” right?

Docker is an open platform that both IT operations teams and Developer team use to build, ship and run their applications, giving them the agility, portability and control that each team requires across the software supply chain.
We have created a standard Docker container that packages up an application, with everything that the applications require to run. This standardization allows teams to containerize applications and run them in any environment, on any infrastructure and to be written in any language

2. What is a Docker container and how is it different than a VM?  Does containerization replace my virtualization infrastructure?

Containerization is very different from virtualization. It starts with the Docker engine, the tool that creates and runs containers (1 or more), and is the Docker installed software on any physical, virtual or cloud host with a compatible OS. Containerization leverages the kernel within the host operating system to run multiple root file systems.

We call these root file systems “containers.” Each container shares the kernel within the host OS, allowing you to run multiple Docker containers on the same host. Unlike VMs, containers do not have an OS within it. They simply share the underlying kernel with the other containers.

Each container running on a host is completely isolated so applications running on the same host are unaware of each other (you can use Docker Networking to create a multi-host overlay network that enables containers running on hosts to speak to one another).

The image below shows containerization on the left and virtualization on the right. Notice how containerization (left), unlike virtualization (right) does not require a hypervisor or multiple OSs.

Docker containers and traditional VMs are not mutually exclusive, so no, containers do not have to replace VMs. Docker containers can actually run within VMs. This allows teams to containerize each service and run multiple Docker containers per vm.

Advanced Docker Interview Questions

3. What’s the benefit of “Dockerizing?

By Dockerizing their environment enterprise teams can leverage the Docker Containers as a Service Platform (CaaS). CaaS gives development teams and IT operations teams agility, portability and control within their environment.

Developers love Docker because it gives them the ability to quickly build and ship applications. Since Docker containers are portable and can run in any environment (with Docker Engine installed on physical, virtual or cloud hosts), developers can go from dev, test, staging and production seamlessly, without having to recode.

This accelerates the application lifecycle and allows them to release applications 13x more often. Docker containers also make it super easy for developers to debug applications, create an updated image and quickly ship an updated version of the application.

IT Ops teams can manage and secure their environment while allowing developers to build and ship apps in a self-service manner. The Docker CaaS platform is supported by Docker, deploys on-premises and is chock full of enterprise security features like role-based access control, integration with LDAP/AD, image signing and many more.

In addition, IT ops teams have the ability to manage to deploy and scale their Dockerized applications across any environment. For example, the portability of Docker containers allows teams to migrate workloads running in AWS over to Azure, without having to recode and with no downtime.

Team cans also migrate workloads from their cloud environment, down to their physical datacenter, and back. This enables teams to utilize the best infrastructure for their business needs, rather than being locked into a particular infrastructure type.

The lightweight nature of Docker containers compared to traditional tools like virtualization, combined with the ability for Docker containers to run within VMs, allowing teams to optimize their infrastructure by 20X, and save money in the process.

4. From an infrastructure standpoint, what do I need from Docker? Is Docker a piece of hardware running in my datacenter, and how taxing is it on my environment?

The Docker engine is the software that is installed on the host (bare metal server, VM or public cloud instance) and is the only “Docker infrastructure” you’ll need. The tool creates, runs and manages Docker containers. So actually, there is no hardware installation necessary at all.

The Docker Engine itself is very lightweight, weighing in around 80 MB total.

Docker Container Interview Questions

5. What exactly do you mean by “Dockerized node”? Can this node be on-premises or in the cloud?

A Dockerized node is anything i.e a bare metal server, VM or public cloud instance that has the Docker Engine installed and running on it.

Docker can manage nodes that exist on-premises as well as in the cloud. Docker Datacenter is an on-premises solution that enterprises use to create, manage, deploy and scale their applications and comes with support from the Docker team.

It can manage hosts that exist in your data centre as well as in your virtual private cloud or public cloud provider (AWS, Azure, Digital Ocean, SoftLayer etc.).

6. Do Docker containers package up the entire OS and make it easier to deploy?

Docker containers do not package up the OS. They package up the applications with everything that the application needs to run. The engine is installed on top of the OS running on a host. Containers share the OS kernel allowing a single host to run multiple containers.

7. What OS can the Docker Engine run on?

The Docker Engine runs on all modern Linux distributions. We also provide a commercially supported Docker Engine for Ubuntu, CentOS, OpenSUSE, RHEL. There is also a technical preview of Docker running on Windows Server 2016.

IT Admin Docker Interview Questions

8. How does Docker help manage my infrastructure? Do I containerize all my infrastructure or something?

Docker isn’t focused on managing your infrastructure. The platform, which is infrastructure agnostic, manages your applications and helps ensure that they can run smoothly, regardless of infrastructure type via solutions like Docker Datacenter. This gives your company the agility, portability and controls you require. Your team is responsible for managing the actual infrastructure.

9. How many containers can run per host?

As far as the number of containers that can be run, this really depends on your environment. The size of your applications as well as the number of available resources (i.e like CPU) will all affect the number of containers that can be run in your environment. Containers, unfortunately, are not magical. They can’t create a new CPU from scratch. They do, however, provide a more efficient way of utilizing your resources. The containers themselves are super lightweight (remember, shared OS vs individual OS per container) and only last as long as the process they are running. Immutable infrastructure if you will.

10. What do I have to do to begin the “Dockerization process”

The best way for your team to get started is for your developers to download Docker for Mac or Docker Windows. These are native installations of Docker on a Mac or Windows device.

From there, developers will take their applications and create a Dockerfile. The Dockerfile is where all of the application configurations are specified. It is essentially the blueprint for the Docker Image.

The image is a snapshot of your application and is what the Docker Engine looks at so it knows what the container it is spinning up should look like.