305-300 Questions and Answers

 Nested page table extensions, such as Intel Extended Page Table (EPT) or AMD Rapid Virtualization Indexing (RVI), are hardware features that facilitate the virtualization of memory. They allow the CPU to perform the translation of guest virtual addresses to host physical addresses in a single step, without the need for software-managed shadow page tables. This reduces the overhead and complexity of memory management for virtual machines, and improves their performance and isolation. Nested page table extensions do not directly affect the virtualization of other hardware components, such as network interfaces, host bus adapters, hard disks, or IO cache.

References:

• Second Level Address Translation - Wikipedia
• c - What is use of extended page table? - Stack Overflow
• Hypervisor From Scratch – Part 4: Address Translation Using Extended …

 The correct way to start a new container that shares the /data volume with the datastore container is to use the --volumes-from flag. This flag mounts all the defined volumes from the referenced containers. In this case, the datastore container has a volume named /data, which is mounted in the service container at the same path. The other options are incorrect because they either use invalid flags, such as --share-with or --volume-backend, or they create new volumes instead of sharing the existing one, such as -v datastore:/data or -v /data. References:

• Docker Docs - Volumes
• Stack Overflow - How to map volume paths using Docker’s --volumes-from?
• Docker Docs - docker run

 Container-based virtualization is a method of operating system-level virtualization that allows multiple isolated user spaces (containers) to run on the same host system1. Each container shares the same operating system kernel as the host, but has its own file system, libraries, and processes2. Therefore, the statements A and C are false, as containers do not run their own kernels or rely on hardware support from the CPU. The statement E is also false, as Linux does support container-based virtualization through various technologies, such as cgroups, namespaces, LXC, Docker, etc12. The statement B is true, as different containers may use different distributions of the same operating system, such as Debian, Ubuntu, Fedora, etc., as long as they are compatible with the host kernel3. The statement D is also true, as all containers run within the operating system kernel of the host system, which provides isolation and resource management for them12. References:

• 1: Containerization (computing) - Wikipedia.
• 2: What are containers? | Google Cloud.
• 3: What is Container-Based Virtualization? - StackHowTo.

• Both Vagrant and Docker can share directories from the host file system to a guest. This allows the guest to access files and folders from the host without copying them. Vagrant uses the config.vm.synced_folder option in the Vagrantfile to specify the shared folders1. Docker uses the -v or --volume flag in the docker run command to mount a host directory as a data volume in the container2.
• Both Vagrant and Docker can download required base images. Base images are the starting point for creating a guest environment. Vagrant uses the config.vm.box option in the Vagrantfile to specify the base image to use1. Docker uses the FROM instruction in the Dockerfile to specify the base image to use2. Both Vagrant and Docker can download base images from public repositories or local sources.
• Both Vagrant and Docker can apply changes to a base image. Changes are modifications or additions to the base image that customize the guest environment. Vagrant uses provisioners to run scripts or commands on the guest after it is booted1. Docker uses instructions in the Dockerfile to execute commands on the baseimage and create a new image2. Both Vagrant and Docker can save the changes to a new image or discard them after the guest is destroyed.
• Vagrant and Docker differ in how they start system images. Vagrant starts system images as virtual machines by default, using a provider such as VirtualBox, VMware, or Hyper-V1. Docker starts system images as containers by default, using the native containerization functionality on macOS, Linux, and Windows2. Containers are generally more lightweight and faster than virtual machines, but less secure and flexible. References: 1: Vagrant vs. Docker | Vagrant | HashiCorp Developer 2: Vagrant vs Docker: Which Is Right for You? (Could Be Both) - Kinsta® Web Development Tools

Cloud-init is a tool that allows users to customize the configuration and behavior of cloud instances during the boot process. Cloud-init can process different kinds of data that are passed to the instance via user-data, which is a mechanism provided by various cloud providers to inject data into the instance. Among the kinds of data that cloud-init can process directly from user-data are:

• Shell scripts to execute: Cloud-init can execute user-data that is formatted as a shell script, starting with the #!/bin/sh or #!/bin/bash shebang. The script can contain any commands that are valid in the shell environment of the instance. The script is executed as the root user during the boot process12.
• Lists of URLs to import: Cloud-init can import user-data that is formatted as a list of URLs, separated by newlines. The URLs can point to any valid data source that cloud-init supports, such as shell scripts, cloud-config files, or include files. The URLs are fetched and processed by cloud-init in the order they appear in the list13.
• cloud-config declarations in YAML: Cloud-init can process user-data that is formatted as a cloud-config file, which is a YAML document that contains declarations for various cloud-init modules. The cloud-config file can specify various aspects of the instance configuration, such as hostname, users, packages, commands, services, and more. The cloud-config file must start with the #cloud-config header14.

The other kinds of data listed in the question are not directly processed by cloud-init from user-data. They are either not supported, not recommended, or require additional steps to be processed. These kinds of data are:

• ISO images to boot from: Cloud-init does not support booting from ISO images that are passed as user-data. ISO images are typically used to install an operating system on a physical or virtual machine, not to customize an existing cloud instance. To boot from an ISO image, the user would need to attach it as a secondary disk to the instance and configure the boot order accordingly5.
• Base64-encoded binary files to execute: Cloud-init does not recommend passing binary files as user-data, as they may not be compatible with the instance’s architecture or operating system. Base64-encoding does not change this fact, as it only converts the binary data into ASCII characters. To execute a binary file, the user would need to decode it and make it executable on the instance6.

References:

• User-Data Formats — cloud-init 22.1 documentation
• User-Data Scripts
• Include File
• Cloud Config
• How to Boot From ISO Image File Directly in Windows
• How to run a binary file as a command in the terminal?.

VirtualBox is a hosted hypervisor, which means it runs as an application on top of an existing operating system, not as a special kernel that is booted before the first regular operating system starts1. VirtualBox supports a large number of guest operating systems, including Windows, Linux, Solaris, OS/2, and OpenBSD1. VirtualBox does not require dedicated shared storage, as it can store virtual machine disk images locally on block devices of the virtualization host, or on network shares, or on iSCSI targets1. VirtualBox provides both a graphical user interface (GUI) and command line tools (VBoxManage) to administer virtual machines1. VirtualBox is available for Windows, Linux, macOS, and Solaris hosts1, and does not require the source code of the currently running Linux kernel to be available. References:

• Oracle VM VirtualBox: Features Overview

Capabilities are a way of implementing fine-grained access control in Linux. They are a set of flags that define the privileges that a process can have. By default, a process inherits the capabilities of its parent, but some capabilities can be dropped or added by the process itself or by the kernel. In the context of container virtualization, capabilities are used to prevent processes from performing actions that might infringe the container, such as accessing the host’s devices, mounting filesystems, changing the system time, or killing other processes. Capabilities allow containers to run with a reduced set of privileges, enhancing the security and isolation of the container environment. For example, Docker uses a default set of capabilities that are granted to the processes running inside a container, and allows users to add or drop capabilities as needed12. References:

• Capabilities | Docker Documentation1
• Linux Capabilities: Making Them Work in Containers2

 The command vagrant init is used to initialize the current directory to be a Vagrant environment by creating an initial Vagrantfile if one does not already exist1. The Vagrantfile contains the configuration settings for the Vagrant box, such as the box name, box URL, network settings, synced folders, provisioners, etc. The command vagrant init does not execute any provisioning tool, start any box, install Vagrant on a Linux host, or download any box. Those actions are performed by other Vagrant commands, such as vagrant provision, vagrant up, vagrant install, and vagrant box add, respectively. References:

• 1: vagrant init - Command-Line Interface | Vagrant | HashiCorp Developer

The FROM statement in a Dockerfile specifies the base image from which the subsequent instructions are executed1. The value of the FROM statement can be either an image name, an image name with a tag, or an image ID1. The image name can be either a repository name or a repository name with a registry prefix2. For example, ubuntu is a repository name, and docker.io/ubuntu is a repository name with a registry prefix2. The tag is an optional identifier that can be used to specify a particular version or variant of an image1. For example, ubuntu:focal refers to the image with the focal tag in the ubuntu repository2. The image ID is a unique identifier that is automatically generated when an image is built or pulled1. For example, sha256:9b0dafaadb1cd1d14e4db51bd0f4c0d56b6b551b2982b2b7c637ca143ad605d2 is an image ID3.

Therefore, the only valid value in the FROM statement among the given options is ubuntu:focal, which is an image name with a tag. The other options are invalid because:

• docker://ubuntu:focal is not a valid image name format. The docker:// prefix is used to specify a transport protocol, not a registry prefix4.
• registry:ubuntu:focal is not a valid image name format. The registry prefix should be a valid hostname or IP address, not a generic term2.
• file:/tmp/ubuntu/Dockerfile is not a valid image name format. The file: prefix is used to specify a local file path, not an image name5.
• http://docker.example.com/images/ubuntu-focal.iso is not a valid image name format. The http:// prefix is used to specify a web URL, not an image name5.

References:

• 1: Dockerfile reference | Docker Docs
• 2: docker - Using FROM statement in dockerfile - Stack Overflow
• 3: How to get the image id from a docker image - Stack Overflow
• 4: skopeo - Docker Registry v2 API tool - Linux Man Pages (1)
• 5: How to build a Docker image from a local Dockerfile? - Stack Overflow

• The purpose of the packer inspect subcommand is to display an overview of the configuration contained in a Packer template1. A Packer template is a file that defines the various components a Packer build requires, such as variables, sources, provisioners, and post-processors2. The packer inspect subcommand can help you quickly learn about a template without having to dive into the HCL (HashiCorp Configuration Language) itself1. The subcommand will tell you things like what variables a template accepts, the sources it defines, the provisioners it defines and the order they’ll run, and more1.
• The other options are not correct because:

The command lxc-checkpoint is used to checkpoint and restore containers. Checkpointing a container means saving the state of the container, including its memory, processes, file descriptors, and network connections, to a file or a directory. Restoring a container means resuming the container from the saved state, as if it was never stopped. Checkpointing and restoring containers can be useful for various purposes, such as live migration, backup, debugging, or snapshotting. The command lxc-checkpoint has the following syntax:

lxc-checkpoint {-n name} {-D path} [-r] [-s] [-v] [-d] [-F]

The options are:

• -n name: Specify the name of the container to checkpoint or restore.
• -D path: Specify the path to the file or directory where the checkpoint data is dumped or restored.
• -r, --restore: Restore the checkpoint for the container, instead of dumping it. This option is incompatible with -s.
• -s, --stop: Optionally stop the container after dumping. This option is incompatible with -r.
• -v, --verbose: Enable verbose criu logging. Only available when providing -r.
• -d, --daemon: Restore the container in the background (this is the default). Only available when providing -r.
• -F, --foreground: Restore the container in the foreground. Only available when providing -r.

The command lxc-checkpoint uses the CRIU (Checkpoint/Restore In Userspace) tool to perform the checkpoint and restore operations. CRIU is a software that can freeze a running application (or part of it) and checkpoint it to a hard drive as a collection of files. It can then use the files to restore and run the application from the point it was frozen at1.

The other statements about the command lxc-checkpoint are not correct. It does not create a clone or an image of a container, nor does it double the memory consumptionof the container. It can work on both running and stopped containers, depending on the options provided. References:

• Linux Containers - LXC - Manpages - lxc-checkpoint.12
• lxc-checkpoint(1) - Linux manual page - man7.org3
• CRIU4

IaaS is a type of cloud computing service that offers essential compute, storage, and networking resources on demand, on a pay-as-you-go basis. IaaS is one of the four types of cloud services, along with software as a service (SaaS), platform as a service (PaaS), and serverless12. IaaS eliminates the need for enterprises to procure, configure, or manage infrastructure themselves, and they only pay for what they use23. Some examples of IaaS providers are Microsoft Azure, Google Cloud, and Amazon Web Services.

LXC implements system containers, which are a type of operating-system-level virtualization. System containers allow running multiple isolated Linux systems on a single Linux control host, using a single Linux kernel. System containers share the same kernel with the host and each other, but have their own file system, libraries, andprocesses. System containers are different from application containers, which are designed to run a single application or service in an isolated environment. Application containers are usually smaller and more portable than system containers, but also more dependent on the host kernel and libraries. Hardware containers, CPU emulation, and paravirtualization are not related to LXC, as they are different kinds of virtualization methods that involve hardware abstraction, instruction translation, or modification of the guest operating system. References:

• 1: LXC - Wikipedia
• 2: Linux Virtualization : Linux Containers (lxc) - GeeksforGeeks
• 3: Features - Proxmox Virtual Environment