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Containers and Virtualization

Deploying and managing containers and virtual machines.

Covers the deployment, management, and orchestration of containers and virtualization technologies in Linux environments.
5 minutes 5 Questions

In the context of CompTIA Linux+, Virtualization and Containerization are distinct methods for deploying environments and managing system resources. Virtualization relies on a Hypervisor to emulate physical hardware, allowing multiple Virtual Machines (VMs) to run simultaneously. Linux+ covers Typ…

Concepts covered: Container Basics (Docker/Podman), Container Orchestration Concepts (Kubernetes), Virtual Machine Management

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Linux+ - Containers and Virtualization Example Questions

Test your knowledge of Containers and Virtualization

Question 1

An administrator includes the instruction `EXPOSE 3000` in a Dockerfile for a Node.js application. After building the image and starting the container using `docker run -d node-app`, the administrator attempts to curl localhost:3000 on the host but the connection is refused. What is the technical reason for this connectivity failure?

Correct Answer: The instruction functions as image metadata and relies on specific runtime flags to establish host mapping

The EXPOSE instruction in a Dockerfile is purely documentation metadata that indicates which ports the container listens on internally, but it does not actually publish or map ports to the host. To make the port accessible from the host, you must use the -p or -P flag at runtime, such as docker run -d -p 3000:3000 node-app.

The security policy answer incorrectly attributes the issue to container isolation policies rather than missing port mapping. The kernel bind conflict is incorrect since no host binding was attempted. The bridge network answer is wrong because Docker's default bridge network works automatically without manual configuration.

Key concept tested: Docker EXPOSE instruction versus runtime port publishing with the -p flag.

Question 2

A Linux administrator configures a Kubernetes Deployment for a critical banking application using the RollingUpdate strategy. To maintain strict availability standards during application updates, the configuration must limit the number of Pods that are allowed to be offline simultaneously relative to the desired replica count. Which parameter specifically controls this lower bound of operational capacity?

Correct Answer: The maxUnavailable configuration field

The correct answer is the maxUnavailable configuration field.

In a Kubernetes Deployment using the RollingUpdate strategy, the maxUnavailable parameter specifies the maximum number of Pods that can be unavailable during the update process. This ensures that at least a certain percentage or number of Pods remain running to handle requests, thereby maintaining the required availability standards.

The maxSurge deployment attribute controls how many Pods can be created above the desired number of replicas during an update, rather than how many can be unavailable.

The terminationGracePeriodSeconds setting defines the duration the system waits for a Pod to shut down gracefully before forcibly killing it.

The minReadySeconds availability timer determines the minimum number of seconds a Pod must be ready without any of its containers crashing for it to be considered available.

Question 3

A Linux administrator needs to establish a secure remote management session to a KVM hypervisor at IP address 192.168.10.5. The connection must use the SSH protocol, authenticate as the user 'remote_admin', and grant control over the system-wide privileged libvirt daemon to manage all virtual machines on the host. Which connection URI successfully establishes this channel?

Correct Answer: qemu+ssh://remote_admin@192.168.10.5/system

The correct connection URI is qemu+ssh://remote_admin@192.168.10.5/system.

To manage KVM virtual machines via libvirt extensively, the standard syntax for the connection URI is driver+transport://user@host/path.

  1. Driver: Even though the hypervisor is KVM, libvirt uses the 'qemu' driver to manage both QEMU and KVM instances. Therefore, the URI must start with 'qemu'.
  2. Transport: The requirement specifies the SSH protocol, which is denoted by appending '+ssh' to the driver name, resulting in 'qemu+ssh'.
  3. Authentication: The user 'remote_admin' at the IP '192.168.10.5' is formatted as 'remote_admin@192.168.10.5'.
  4. Path/Scope: The requirement defines a need to control the 'system-wide privileged libvirt daemon'. In libvirt, the path '/system' connects to the privileged system daemon (root), whereas '/session' connects to an unprivileged per-user instance.

The other answers are incorrect because:
- Using 'kvm' as the protocol prefix is not the standard driver name for libvirt URIs; 'qemu' is used for KVM management.
- The '+tls' transport uses SSL/TLS certificates rather than SSH, and the '/session' path would not grant system-wide control over all VMs.
- Appending query parameters like '?tunnel=ssh' is not the correct syntax for defining the transport protocol; the transport must be defined in the URI scheme (prefix).

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