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Hence, if you are looking for boosting up your profile and securing your future, Docker will help you in reaching the zenith of your career. Apart from this, you would also have a lot of opportunities as a fresher.
These questions alone are omnipotent. Read and re-read the questions and their solutions to get accustomed to what you will be asked in the interview. These Docker interview questions and answers will also help you on your way to mastering the skills and will take you to the giant world where worldwide and local businesses, huge or medium, are picking up the best and quality Docker professionals.
This ultimate list of best Docker interview questions will ride you through the quick knowledge of the subject and topics like Installing Ant, Ant concepts and terminologies, Integrating ANT into your IDE. This Docker interview questions and answers can be your next gateway to your next job as a Docker expert.
These are very Basic Docker Interview Questions and Answers for freshers and experienced both.
Q1: What is Docker?
A1: I will suggest you to start with a small definition of Docker.
Docker is a containerization platform which packages your application and all its dependencies together in the form of containers so as to ensure that your application works seamlessly in any environment be it development or test or production.
Docker containers, wrap a piece of software in a complete filesystem that contains everything needed to run: code, runtime, system tools, system libraries etc. anything that can be installed on a server. This guarantees that the software will always run the same, regardless of its environment.
Q2: What is Docker image?
A2: I will suggest you to go with the below mentioned flow:
Docker image is the source of Docker container. In other words, Docker images are used to create containers. Images are created with the build command, and they’ll produce a container when started with run. Images are stored in a Docker registry such as registry.hub.docker.com because they can become quite large, images are designed to be composed of layers of other images, allowing a minimal amount of data to be sent when transferring images over the network.
Q3: What is Docker hub?
A3: Docker hub is a cloud-based registry service which allows you to link to code repositories, build your images and test them, stores manually pushed images, and links to Docker cloud so you can deploy images to your hosts. It provides a centralized resource for container image discovery, distribution and change management, user and team collaboration, and workflow automation throughout the development pipeline.
Q4: What is Docker Swarm?
A4: Docker Swarm is native clustering for Docker. It turns a pool of Docker hosts into a single, virtual Docker host. Docker Swarm serves the standard Docker API, any tool that already communicates with a Docker daemon can use Swarm to transparently scale to multiple hosts.
I will also suggest you to include some supported tools:
- Docker Compose
- Docker Machine
Q5: Tell us how you have used Docker in your past position?
A5: If you have no past practical experience in Docker and have past experience with other tools in a similar space, be honest and explain the same. In this case, it makes sense if you can compare other tools to Docker in terms of functionality.
Q6: How to stop and restart the Docker container?
A6: In order to stop the Docker container you can use the below command:
1 docker stop container ID
Now to restart the Docker container you can use:
1 docker restart container ID
Q7: Do I lose my data when the Docker container exits?
A7: You can answer this by saying, no I won’t lose my data when Docker container exits, any data that your application writes to disk gets preserved in its container until you explicitly delete the container. The file system for the container persists even after the container halts.
Q8: What platforms does Docker run on?
A8: Docker is currently available on the following platforms and also on the following Vendors or Linux:
- Ubuntu 12.04, 13.04
- Fedora 19/20+
- RHEL 6.5+
- CentOS 6+
- openSUSE 12.3+
- CRUX 3.0+
Docker is currently available and also is able to run on the following Cloud environment setups given as below:
- Amazon EC2
- Google Compute Engine
- Microsoft Azure
Docker is extending its support to Windows and Mac OSX environments and support on Windows has been on the growth in a very drastic manner.
Q9: What, in your opinion, is the most exciting potential use for Docker?
A9: The most exciting potential use of Docker that I can think of is its build pipeline. Most of the Docker professionals are seen using hyper-scaling with containers, and indeed get a lot of containers on the host that it actually runs on. These are also known to be blatantly fast. Most of the development – test build pipeline is completely automated using the Docker framework.
Q10: Is there a possibility to include specific code with COPY/ADD or a volume?
A10: This can be easily achieved by adding either the COPY or the ADD directives in your dockerfile. This will count to be useful if you want to move your code along with any of your Docker images, example, sending your code an environment up the ladder – Development environment to the Staging environment or from the Staging environment to the Production environment.
Having said that, you might come across situations where you’ll need to use both the approaches. You can have the image include the code using a COPY, and use a volume in your Compose file to include the code from the host during development. The volume overrides the directory contents of the image.
Q11: Can you remove a paused container from Docker?
A11: No, it is not possible to remove a container from Docker that is just paused. It is a must that a container should be in the stopped state, before it can be removed from the Docker container.
Q12: Difference between Docker Image and container?
A12: Docker container is the runtime instance of docker image.
Docker Image doesnot have a state and its state never changes as it is just set of files whereas docker container has its execution state.
Q13: How do you think Docker will change virtualization and cloud environments? Do you think cloud technology has a set trajectory, or is there still room for significant change?
A13: I think there are a lot of workloads that Docker is ideal for, as I mentioned earlier both in the hyper-scale world of many containers and in the dev-test-build use case. I fully expect a lot of companies and vendors to embrace Docker as an alternative form of virtualization on both bare metal and in the cloud.
As for cloud technology’s trajectory. I think we’ve seen a significant change in the last couple of years. I think they’ll be a bunch more before we’re done. The question of OpenStack and whether it will succeed as an IAAS alternative or DIY cloud solution. I think we’ve only touched on the potential for PAAS and there’s a lot of room for growth and development in that space. It’ll also be interesting to see how the capabilities of PAAS products develop and whether they grow to embrace or connect with consumer cloud-based products.
Q14: Why is Docker the new craze in virtualization and cloud computing?
A14: It’s OSCON time again, and this year the tech sector is abuzz with talk of cloud infrastructure. One of the more interesting startups is Docker, an ultra-lightweight containerization app that’s brimming with potential
I caught up with the VP of Services for Docker, James Turnbull, who’ll be running a Docker crash course at the con. Besides finding out what Docker is anyway, we discussed the cloud, open source contributing and getting a real job.
Q15: What’s the difference between up, run, and start?
A15: Typically, you want docker-compose up. Use up to start or restart all the services defined in a docker-compose.yml. In the default “attached” mode, you’ll see all the logs from all the containers. In “detached” mode (-d), Compose exits after starting the containers, but the containers continue to run in the background.
The docker-compose run command is for running “one-off” or “ad-hoc” tasks. It requires the service name you want to run and only starts containers for services that the running service depends on. Use run to run tests or perform an administrative task such as removing or adding data to a data volume container. The run command acts like docker run -ti in that it opens an interactive terminal to the container and returns an exit status matching the exit status of the process in the container.
The docker-compose start command is useful only to restart containers that were previously created but were stopped. It never creates new containers.
Q16: Can I use json instead of yaml for my Compose file?
A16: Yes. Yaml is a superset of json so any JSON file should be valid Yaml. To use a JSON file with Compose, specify the filename to use, for example:
docker-compose -f docker-compose.json up
Q17: Can you give us a quick rundown of what we should expect from your Docker presentation at OSCON this year?
A17: It’s very much a crash course introduction to Docker. It’s aimed at Developers and SysAdmins who want to get started with Docker in a very hands on way. We’ll teach the basics of how to use Docker and how to integrate it into your daily workflow.
Q18: Why do my services take 10 seconds to recreate or stop?
A18: Compose stop attempts to stop a container by sending a SIGTERM. It then waits for a default timeout of 10 seconds. After the timeout, a SIGKILL is sent to the container to forcefully kill it. If you are waiting for this timeout, it means that your containers aren’t shutting down when they receive the SIGTERM signal.
There has already been a lot written about this problem of processes handling signals in containers.
To fix this problem, try the following:
Make sure you’re using the JSON form of CMD and ENTRYPOINT in your Dockerfile.
For example use [“program”, “arg1”, “arg2?] not”program arg1 arg2”. Using the string form causes Docker to run your process using bash which doesn’t handle signals properly. Compose always uses the JSON form, so don’t worry if you override the command or entrypoint in your Compose file.
-If you are able, modify the application that you’re running to add an explicit signal handler for SIGTERM.
-Set the stop_signal to a signal which the application knows how to handle:
-web: build: . stop_signal: SIGINT
-If you can’t modify the application, wrap the application in a lightweight init system (like s6) or a signal proxy (like dumb-init or tini). Either of these wrappers take care of handling SIGTERM properly.
Q19: How do I run multiple copies of a Compose file on the same host?
A19: Compose uses the project name to create unique identifiers for all of a project’s containers and other resources. To run multiple copies of a project, set a custom project name using the -p command line option or theCOMPOSE_PROJECT_NAME environment variable.
Q20: Are you operationally prepared to manage multiple languages/libraries/repositories?
A20: Last year, we encountered an organization that developed a modular application while allowing developers to “use what they want” to build individual components. It was a nice concept but a total organizational nightmare — chasing the ideal of modular design without considering the impact of this complexity on their operations.
The organization was then interested in Docker to help facilitate deployments, but we strongly recommended that this organization not use Docker before addressing the root issues. Making it easier to deploy these disparate applications wouldn’t be an antidote to the difficulties of maintaining several different development stacks for long-term maintenance of these apps.
Q21: Do you already have a logging, monitoring, or mature deployment solution?
A21: Chances are that your application already has a framework for shipping logs and backing up data to the right places at the right times. To implement Docker, you not only need to replicate the logging behavior you expect in your virtual machine environment, but you also need to prepare your compliance or governance team for these changes. New tools are entering the Docker space all the time, but many do not match the stability and maturity of existing solutions. Partial updates, rollbacks and other common deployment tasks may need to be reengineered to accommodate a containerized deployment.
If it’s not broken, don’t fix it. If you’ve already invested the engineering time required to build a continuous integration/continuous delivery (CI/CD) pipeline, containerizing legacy apps may not be worth the time investment.
Q22: You say that ansible can take up to 20x longer to provision, but why?
A22: Docker uses cache to speed up builds significantly. Every command in Dockerfile is build in another docker container and it’s results are stored in separate layer. Layers are built on top of each other.
Docker scans Dockerfile and try to execute each steps one after another, before executing it probes if this layer is already in cache. When cache is hit, building step is skipped and from user perspective is almost instant.
When you build your Dockerfile in a way that the most changing things such as application source code are on the bottom, you would experience instant builds.
Another way of amazingly fast building docker images is using good base image – which you specify inFROMcommand, you can then only make necessary changes, not rebuild everything from scratch. This way, build will be quicker. It’s especially beneficial if you have a host without the cache like Continuous Integration server.
Summing up, building docker images with Dockerfile is faster than provisioning with ansible, because of using docker cache and good base images. Moreover you can completely eliminate provisioning, by using ready to use configured images such stgresus.
$ docker run –name some-postgres -d postgres No installing postgres at all – it’s ready to run.
Q23: Is Container Technology New?
A23: No, it is not. Different variations of containers technology were out there in *NIX world for a long time.Examples are:-Solaris container (aka Solaris Zones)-FreeBSD Jails-AIX Workload Partitions (aka WPARs)-Linux OpenVZ.
Q24: What Is The Use Case For Docker?
- Well, I think, docker is extremely useful in development environments. Especially for testing purposes. You can deploy and re-deploy apps in a blink of eye.
- Also, I believe there are use cases where you can use Docker in production. Imagine you have some Node.js application providing some services on web. Do you really need to run full OS for this
- Eventually, if docker is good or not should be decided on an application basis. For some apps it can be sufficient, for others not.
Q25: Finally, What Does The Deploy Process Look Like For Dockerized Apps Stored In A Git Repo?
A25: It depends how your production environment looks like.
Example deploy process may look like this:
- Build an app using docker build . in the code directory.
- Test an image.
- Push the new image out to registry docker push myorg/myimage.
- Notify remote app server to pull image from registry and run it (you can also do it directly using some configuration management tool).
- Swap ports in a http proxy.
- Stop the old container.
You can consider using amazon elastic beanstalk with docker or dokku.
Elastic beanstalk is a powerful beast and will do most of deployment for you and provide features such as autoscaling, rolling updates, zero deployment deployments and more.
Dokku is very simple platform as a service similar to heroku.
Q26: Will cloud automation overtake containerization?
A26: At AWS Re:Invent last month, Amazon chief technology officer Werner Vogels spent a significant portion of his keynote on AWS Lambda, an automation tool that deploys infrastructure based on your code. While Vogels did mention AWS’ container service, his focus on Lambda implies that he believes dealing with zero infrastructure is preferable to configuring and deploying containers for most developers.
Containers are rapidly gaining popularity in the enterprise, and are sure to be an essential part of many professional CI/CD pipelines. But as technology experts and CTOs, it is our responsibility to challenge new methodologies and services and properly weigh the risks of early adoption. I believe Docker can be extremely effective for organizations that understand the consequences of containerization — but only if you ask the right questions.
Docker Conclusion Interview FAQs
We know the list of Docker Interview Questions and Answers, Docker Interview Questions and Answers Freshers, Docker Interview Questions and Answers, Docker Interview Questions is overwhelming but the advantages of reading all the questions will maximize your potential and help you crack the interview. The surprising fact is that this Docker interview questions and answers post covers all the basic of the Docker technology and you have to check out the FAQs of different components of Docker too.
However, you will be asked with the questions in the interview related to the above mentioned questions. Preparing and understanding all the concept of Docker technology will help you strengthen the other little information around the topic.
After preparing these interview questions, we recommend you to go for a mock interview before facing the real one. You can take the help of your friend or a Docker expert to find the loop holes in your skills and knowledge. Moreover, this will also allow you in practicing and improving the communication skill which plays a vital role in getting placed and grabbing high salaries.
Remember, in the interview, the company or the business or you can say the examiner often checks your basic knowledge of the subject. If your basics is covered and strengthened, you can have the job of your dream. The industry experts understand that if the foundation of the student is already made up, it is easy for the company to educate the employ towards advance skills. If there are no basics, there is no meaning of having learnt the subject.
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We hope that you enjoyed reading Docker Interview Questions and Answers, Docker Interview Questions and Answers Freshers, Docker Interview Questions and Answers, Docker Interview Questions and all the FAQs associated with the interview. Do not forget to revise all the Docker interview questions and answers before going for the Docker interview. In addition to this, if you’ve any doubt or query associated with Docker, you can contact us anytime. We will be happy to help you out at our earliest convenience. At last, we wish you all the best for your upcoming interview on Docker Technology.