What is a Container? | What is an Image? | Docker Containers and Images | Geekific

Summary

In this video, the speaker explains the concept of Docker containers and their relationship with images. Containers are isolated processes that are assigned specific resources through techniques like namespacing and control groups. Namespacing ensures that each container can access its own set of resources, while control groups limit the amount of resources a container can use. The speaker also clarifies how Docker containers work on non-Linux operating systems, as Docker uses a Linux virtual machine to manage containers on Windows and Mac. The video provides a detailed, yet approachable, explanation of how containers are created and managed.

Takeaways

• 😀 Docker uses containers to isolate and run applications with their required dependencies.
• 😀 A container is not a physical construct, but rather a process with specific resources assigned to it.
• 😀 The kernel of an operating system governs access between running programs and hardware resources.
• 😀 System calls are the way programs communicate with the kernel to access hardware or memory.
• 😀 Namespacing allows you to isolate hardware resources for individual processes or programs.
• 😀 Control groups (cgroups) limit the amount of resources a process can consume, such as memory and CPU.
• 😀 Containers are created by isolating a portion of the hard drive and placing the image snapshot in it.
• 😀 Containers are limited to the resources assigned to them, ensuring that other processes are unaffected.
• 😀 Images are used to create containers by placing necessary dependencies in an isolated segment of the disk.
• 😀 Namespacing and control groups are specific to Linux, which is why Docker uses a Linux virtual machine on Windows or Mac.
• 😀 When running Docker on non-Linux systems, a Linux virtual machine is used to host containers and manage resources.

Q & A

What is Docker and why do we use it?

Docker is a platform that allows developers to package applications and their dependencies into isolated containers. It simplifies the development, deployment, and scalability of applications by ensuring consistency across different environments.

What are the key terms mentioned in the video when discussing Docker?

The key terms discussed in the video are 'Images' and 'Containers'. Images are snapshots of a program's environment, and containers are the running instances of these images that have specific resources assigned to them.

What role does the kernel play in the operating system?

The kernel is a critical part of an operating system that manages the interaction between software applications and the hardware. It acts as an intermediary layer between the processes running on a computer and the physical hardware resources.

How do system calls work in relation to the kernel?

System calls are like method invocations where programs request the kernel to perform tasks, such as reading from or writing to memory, files, or other hardware components. These calls allow programs to interact with the operating system.

What is the problem described in the video regarding running two versions of Python on a computer?

The problem is that when you only have Python version 2 installed, but need Python version 3 for another program, you face a conflict. You can’t install both versions of Python due to system restrictions, which makes it difficult for both programs to run simultaneously.

How does namespacing solve the issue of running two versions of Python?

Namespacing allows you to segment resources on your system, such as hard drive space, and dedicate portions of them to different processes. In this case, it would let one process use Python 2 and another process use Python 3, even if the system only has one version installed.

What is the relationship between containers and namespacing?

Containers leverage namespacing to isolate resources such as memory, storage, and network bandwidth. Each container operates in its own isolated environment, ensuring that the processes within them only have access to the resources assigned to that container.

What is the function of control groups in Docker containers?

Control groups are used to limit the amount of resources, like memory, CPU, disk input/output, and network bandwidth, that a process or container can consume. This ensures that processes don’t exceed their allocated resources.

What is a container in the context of Docker?

A container is a process or a set of processes that are grouped with specific resources allocated to them, such as memory and disk space. It runs in isolation, with the kernel managing its access to these resources.

How does an image turn into a container?

An image is a snapshot of the dependencies and configuration required for a program. When the image is converted into a container, the kernel isolates resources like disk space and memory for the container, places the image's snapshot into that space, and runs the program inside the container.

Why is Docker running on a Linux virtual machine on Windows and Mac?

Docker uses Linux-specific features like namespacing and control groups to manage containers. Since these features are not available by default on Windows or Mac, Docker for these platforms installs a Linux virtual machine to enable the creation and management of containers.

What happens when you run the 'docker version' command on Windows or Mac?

When you run the 'docker version' command on Windows or Mac, it shows that the operating system being used is Linux. This is because Docker relies on a Linux virtual machine to run containers on these platforms.