I have a openvz vps which is centos 7 but with a 2.6 kernel. I know this is not compatible with docker. I have another KVM vps which has docker on it. Is there anyway to access docker in KVM remotely using my openvz vps? Basically I want my openvz box to be my dev machine and Ill deploy to KVM docker. What would be an ideal setup above?
You say the host has a 2.6.x kernel, but that covers a couple different releases. I have made docker work in an openvz VPS on a host with 2.6.32 kernel (derived from RedHat el6) but it would probably not work for kernels 2.6.18 or 2.6.9 (you really should upgrade if you have 2.6.9 as that is based on RedHat el4 kernel, 2.6.18 should be fine until 3/2017). You can find instructions to make it work with a compatible kernel at the openvz wiki. WARNING: docker does not perform very well in this configuration (2.6.32 kernel, CentOS 7 VPS) as you do not get any of the fancy filesystem layering functionality since you are forced to use the "vfs" storage engine. Each layer of the docker container will be a full copy of its underlying filesystem, grossly ballooning disk usage for images with lots of layers.
If you are not running a docker compatible kernel, you would not be able to run any of the docker tools at all, so your options are limited. If you still want to develop docker containers on your VPS to move to your KVM, you could use chroot and yum/rpm to construct your container and make a ${docker_image}.tgz file on your VPS and then copy that to your KVM and import into docker.
Hope that helps.
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Every Docker image, as I understand, is based on base image - for example, Ubuntu.
And if I want to isolate any process I should deploy ubuntu docker base image (where is difference with Vagrant here?), and create a necessary subimage after it installing on ubuntu image?
So, if Ubuntu is launched on Vagrant and on Docker, where is practice difference?
And if to use docker provider in Vagrant - where here is difference between Vagrant and Docker?
And, in Docker is it possible to isolate processes on some PC without base image without it's sharing to another PC?
Vagrant is a utility to help you automate setting up VMs. Docker is a utility that helps you use containerization in linux.
A virtual machine runs a whole system, and emulates hardware. Containers section off processes in a single running kernel without emulating hardware.
Both a VM and a Docker image may be Ubuntu 14.04, but with the Docker image you don't need to run the whole OS.
For example, if I want to run an nginx container based on ubuntu, I'd end up with only the nginx process running. No upstart/systemd/init is needed. A VM would run an init system, manage its own networking, and run other services as well. The container image approach that uses a linux distro base is mostly for convenience.
It is entirely possible to run Docker containers with very minimal images. A statically compiled binary alone in an image is all you'd need to run a container.
Vagrant : Vagrant is a project that helps the spawning of virtual machines. It started as an command line of VirtualBox, something similar to Gemfile for VM's. You can choose the base image to start with, network, IP, share folders and put it all in a file that anyone can reuse to spawn the same configured machine. Vagrant has different extensions, provisioning options and VM providers. You can run a VirtualBox, VMware and it is extensible enough to be able to create instances on EC2.
Docker : Docker, allows to package an application with all of its dependencies into a standardized unit of software development. So, it reduces a friction between developer, QA and testing. It dynamically change your application, adding new capabilities every single day, scaling out services to quickly changing the problem areas. Docker is putting itself in an excited place as the interface to PaaS be it networking, discovery and service discovery with applications not having to care about underlying infrastructure. Yes, their are still issues with docker in production, but, hopefully, we'll see the solutions to those problems, as docker team and contributors working hard on those issues. As Docker Volume driver allows third-party container data management solutions to provide data volumes for containers which operate on data, such as database, key-value stores, and other stateful applications. The latest version is coming with much more flexibility, complete orchestration build-in, advanced networking, secrets management, etc. As you can see one, rexray, as volume plugin and provides advanced storage functionality. emccode/rexray We're finally starting to agree on more than just images and run time.
In every docker tutorial, one of the main advantages of the docker is that docker container use host OS. But if that is true, I don't understand why I need to include OS in the image. For example here is image of centOS. I understand that if I want to run centOS in container I must pull this image but where then host OS come? It would be best if someone can point me to some link to read about that because I cannot find appropriate one.
What Docker uses of the host is actually only the OS's kernel.
What you include in the Docker container is not the actual OS (i.e., the kernel), but rather all the files that make up a specific distribution, such as Ubuntu or Fedora, or whatever…
This is also the reason why you can't run Linux containers on Windows and vice-versa (without a VM), because Linux software of course doesn't work with the Windows kernel, and Windows software doesn't work with the Linux kernel.
So, all Docker containers running on a given host share the host OS's kernel.
It actually shares the kernel & required libraries to boot the image from host OS. That's why those images are really small & not like traditional ISO files. It primarily utilizes union file system, cgroups and namespaces to manage the images and containers.
You can give a quick read to below -
https://kjanshair.github.io/2017/07/04/Docker-Containers-vs-System-Processes/
How is Docker different from a normal virtual machine?
I am running a RHEL 7 server and I am deploying containers using docker. Since you need to have RHEL servers and containers registered with RHN, I am now thinking of using centos7 docker images rather than RHEL7 ones, to avoid the RHN hassles.
Can anybody see any downside to doing it this way?
Since the kernel is the same you can use any distro available: Why docker has ability to run different linux distribution?.
For example many projects are moving to Alpine Linux because it give you the ability to build very small images: see Docker Official Images are Moving to Alpine Linux.
Have been trying to learn Docker and one thing that puzzles me is how a different flavour of Linux (to the host OS) actually runs in the Docker container.
If we assume my Docker host is running RedHat and I start a container from an Ubuntu image then are the following true?:
logically speaking, if the Ubuntu image footprint is around 550MB then will the Docker Daemon actually download (from an image registry) 550MB worth of Ubuntu image in order to create the Container?
is the instance of Ubuntu running in the container essentially no different than if I had downloaded and installed the same version manually?
I'm aware that the Docker container shares the same kernel used by the host OS and that one of the fundamental points of Docker was its efficiency gains of the container using the underlying OS. So Im a bit confused about what actually happens when you start a Container created from a different Linux version than the host.
I think this previous post may help you understand it a little more - Docker container isolation, does it care about underlying Linux OS?.
The crux of the matter is that if the Host OS is RedHat then it is the RedHat kernel which will be used by whatever build of Linux you run in your Docker container ie. Ubuntu in your example.
This comes down to understanding what the difference is between a Linux OS and a Linux Image. You will not be running a full Ubuntu OS inside the Docker Container but an image of Ubuntu.
For the purpose of your question think:-
OS = kernel + filesystem/libraries
Image = filesystem/libraries
The Ubuntu image running inside your Docker container is just the Ubuntu filesystem/libraries - it will not contain the Ubuntu kernel. This partly explains the efficiencies you get from a Docker container which is leveraging the Kernel (among other things) of the underlying Host.
The Ubuntu image running inside the Docker container runs in what is called the user space for that container. This image can make kernel system calls to the RedHat host OS kernel (as part of transferring control from user space to kernel space for some user operations). Since the core kernel is common technology, the system calls are expected to be compatible even when the call is made from an Ubuntu user space code to a Redhat kernel code. This compatibility make it possible to share the kernel across containers which may all have different base OS images.
Every Docker image, as I understand, is based on base image - for example, Ubuntu.
And if I want to isolate any process I should deploy ubuntu docker base image (where is difference with Vagrant here?), and create a necessary subimage after it installing on ubuntu image?
So, if Ubuntu is launched on Vagrant and on Docker, where is practice difference?
And if to use docker provider in Vagrant - where here is difference between Vagrant and Docker?
And, in Docker is it possible to isolate processes on some PC without base image without it's sharing to another PC?
Vagrant is a utility to help you automate setting up VMs. Docker is a utility that helps you use containerization in linux.
A virtual machine runs a whole system, and emulates hardware. Containers section off processes in a single running kernel without emulating hardware.
Both a VM and a Docker image may be Ubuntu 14.04, but with the Docker image you don't need to run the whole OS.
For example, if I want to run an nginx container based on ubuntu, I'd end up with only the nginx process running. No upstart/systemd/init is needed. A VM would run an init system, manage its own networking, and run other services as well. The container image approach that uses a linux distro base is mostly for convenience.
It is entirely possible to run Docker containers with very minimal images. A statically compiled binary alone in an image is all you'd need to run a container.
Vagrant : Vagrant is a project that helps the spawning of virtual machines. It started as an command line of VirtualBox, something similar to Gemfile for VM's. You can choose the base image to start with, network, IP, share folders and put it all in a file that anyone can reuse to spawn the same configured machine. Vagrant has different extensions, provisioning options and VM providers. You can run a VirtualBox, VMware and it is extensible enough to be able to create instances on EC2.
Docker : Docker, allows to package an application with all of its dependencies into a standardized unit of software development. So, it reduces a friction between developer, QA and testing. It dynamically change your application, adding new capabilities every single day, scaling out services to quickly changing the problem areas. Docker is putting itself in an excited place as the interface to PaaS be it networking, discovery and service discovery with applications not having to care about underlying infrastructure. Yes, their are still issues with docker in production, but, hopefully, we'll see the solutions to those problems, as docker team and contributors working hard on those issues. As Docker Volume driver allows third-party container data management solutions to provide data volumes for containers which operate on data, such as database, key-value stores, and other stateful applications. The latest version is coming with much more flexibility, complete orchestration build-in, advanced networking, secrets management, etc. As you can see one, rexray, as volume plugin and provides advanced storage functionality. emccode/rexray We're finally starting to agree on more than just images and run time.