Top 100+ DOCKER Interview Questions And Answers

Docker in Java is a containerization platform that packages applications & their dependencies into containers to ensure the applications work seamlessly in any environment. Docker containers enclose a piece of software in a filesystem that covers everything required to run, such as code, system tools, libraries, runtime, etc. It includes anything that can be installed on the server. It guarantees that the software will run the same, regardless of any environment.

Answer:

Docker container offers several benefits to both developers & system administrators, including:

• Rapid app deployment– Docker containers have a minimal runtime requirement of applications which reduces the size & allows quicker deployment.
• Portability across different machines– An application & its dependency can be wrapped in a single container, independent from the host version of a Linux kernel, deployment model, or platform distribution. The container can be transferred to another machine that runs Docker & executed without any compatibility issues.
• Version control & component reusability– One can track successive versions of the Docker container, inspect differences & roll-back to previous versions. The container reuses the components from preceding layers that makes it noticeably lightweight.
• Sharing– You can deploy the remote repository to share your Docker container with others. For this purpose, Red Hat offers a registry. It is also possible to configure your private repository.
• Minimal overhead & Lightweight footprint– Docker images are relatively very small, which facilitates rapid delivery & reduces time to deploy new app containers.
• Simplified maintenance– Docker container reduces efforts & risks of problems with app dependencies.

Answer:

Docker provides several features; some of them are listed below:

• Faster and Easier configuration: Docker helps to configure the systems in an easier & faster way. This feature enables code deployment in less time with minimal effort.
• Application isolation: Docker containers run applications in an isolated environment. As each container is independent, the Docker can execute any application.
• Boost productivity: Docker helps in increasing productivity by streamlining the technical configuration & deploying applications quickly. Besides, it also provides an isolated environment to execute each application & reduces the resources.
• Swarm: Docker provides Swarm, a scheduling & clustering tool. It enables you to create & manage a cluster of multiple Docker containers deployed in multiple host machines. Swarm offers high-level availability for applications.
• Security Management: Dover saves secrets into swarm mode & gives service access to certain secrets, including a few essential commands to the engine like secret create, secret inspect, etc.
• Rapid scaling: Docker containers need less computing hardware. They enable data center operators to cram more workload in less hardware, resulting in lower costs.
• Better Software Delivery: Docker containers offers more efficient software delivery as they are self-contained, portable, & have isolated disk volume. This isolated volume goes well with the container as it develops and deployed to many environments.
• Software-defined networking: Docker supports software-defined networking. It means that without touching a router, the Docker CLI allows the operators to define isolated networks. Developers & operators design systems with complex network topologies & define the networks in the configuration files.
• Reduce the Size: Docker provides a smaller Operating System footprint through containers that can reduce the development size.

Answer:

Here are a few notable drawbacks of Docker:

• It doesn’t provide a storage option;
• Docker offers a poor monitoring option;
• There is no automatic rescheduling of inactive nodes in Docker;
• It complicates the automatic horizontal scaling setup.

Answer:

A Docker image is a file used to execute code in a Docker container. Docker images act as a set of instructions to build a Docker container, like a template. Docker images also act as the starting point when using Docker. An image is comparable to a snapshot in virtual machine (VM) environments.

Answer:

Docker Engine is defined as an open-source containerization technology that streamlines development, shipping, assembling, & running applications by using the following components:

• Docker Daemon
• Docker CLI
• Docker Engine REST API

Answer:

Docker Registry is a highly scalable, server-side, stateless application that stores & distributes Docker images. There are two types of Docker Registry:

• Public Registry
• Private Registry

Answer:

The memory-swap is a modifier flag that has a meaning only when the memory is also set. Swap allows the container to write excess memory requirements to a disk when it has exhausted its RAM. There is also a performance penalty for the applications that swap memory often to disk.

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Docker Swarm means the native clustering for Docker. It transforms a pool of Docker hosts into one virtual Docker host. Swarm serves the standard Docker Application Programming Interface. Any tool that communicates with a Docker Daemon can deploy Swarm to scale to multiple hosts transparently.

Answer:

Following are the main states of Docker container are:

• Created: When you create a new Docker container, you will see the “Created” state for your Docker container. In Created state, the container is not yet started.
• Restarting: When you restart a Docker container due to any problem, you will see the Restarting state.
• Running: It is the central state you will see for your Docker container. It indicates that the container has started with no problem detected in it.
• Paused: When you pause the process of a Docker container or temporarily stop it from running via docker pause, you’ll see Paused state until you unpause it.
• Exited: If your container has been stopped due to a problem or your Docker container is stopped manually, you’ll see your container in the Exited state, based on your restart policy.
• Dead: A Docker container that the daemon tried & failed to stop (due to a busy resource or devise used by the container).

Answer:

Docker Hub is a service provided by Docker for sharing & finding the container images. The default version of Docker Hub is the cloud-based registry that hosts public Docker images such as Linux, Ubuntu, etc. One needs to create repositories to push & pull the Docker images, thus enabling us to share container images within an organization, team, & customers. A single Docker Hub repository can hold several Docker images. It also allows developers to link repositories with GitHub to automate building, deploying, & testing application images. It provides a centralized resource for distribution, container image discovery, collaboration, change management, & workflow automation throughout the development pipeline.

Answer:

Virtualization is defined as the process of building a software-based virtual version of storage, servers, compute, application, etc. These virtual environments or versions are created through a single physical hardware system. Virtualization helps you split a system into multiple different sections, which acts like a separate or distinctive individual system. A hypervisor is software that makes such type of splitting possible. The virtual version or environment created by the Hypervisor is known as the Virtual Machine.

Answer:

Hypervisor refers to software that enables Virtualization. It is also known as Virtual Machine Monitor. Hypervisor divides the host system & allocates resources to each segregated virtual environment. Thus, one can have multiple Operating Systems on a single host system. There are mainly two types of Hypervisors, as follows:

• Type 1: Native Hypervisor, also known, as Bare-metal Hypervisor; this type of Hypervisor runs directly on the underlying host system. It has direct access to a host’s system hardware; hence it doesn’t require a base server OS.
• Type 2: Hosted Hypervisor is the second type that utilizes the underlying host OS.

Answer:

Docker object labels are a key-value pair stored as a string. You can apply metadata using labels for Docker objects such as volumes, containers, images, services, networks, local daemons, & swarm nodes. A key-value pair needs to be unique for each object. Labels are static for the entire object’s lifetime.

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Container Networking Model, abbreviated as CNM, is a specification from Docker, Inc. that forms the basis of container networking in the Docker environment. This Docker’s approach offers container networking with support for multiple network drivers.

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Yes, Docker do provide support for IPv6. IPv6 is only supported when Docker daemons runs on Linux hosts. However, if want to enable IPv6 networking in the Docker daemon, you need to modify /etc/docker/daemon.json & set the ipv6 key as true.

Answer:

DTR or Docker Trusted Registry is an image storage solution to manage & storage the Docker images securely. Docker Trusted Registry is available on private cloud or premises. DTR can be used during CD/CI processes for delivering, running, & building applications. DTR has a built-in access control & is efficient.

Answer:

Docker namespace is a crucial concept of containers & an important Linux feature. It adds a layer of isolation to the containers. Docker offers multiple namespaces to stay portable & not affect an underlying host system. Some types of Docker Namespace are Mount, User, PID, IPC, & Network.

Answer:

Containerization is a type of Virtualization that helps you run applications in containers or isolated user-spaces, all using a shared Operating System. It encapsulates or packs software code and its dependencies of applications to let them run in a consistent & uniform manner on any environment or infrastructure.

Answer:

1. Virtualization helps developers to host & run multiple Operating Systems on the hardware of a single physical server. In contrast, Containerization helps developers to deploy multiple apps using the same operating system on a single server or Virtual Machine.
2. Hypervisors provide complete Virtual Machines to the guest OS. Containers ensure user spaces or isolated environments for running applications. On the other hand, in virtualization, any changes within a container don’t reflect on the host & other containers of the same host.
3. The Virtual Machines (VMs) form an abstraction of the system hardware layer. It means that each Virtual Machine on the host acts as a physical machine whereas Containers form an abstraction of the application layer. It means that each container constitutes a different application.