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Ask HN: What is the actual purpose of Docker?

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Re: Ask HN: What is the actual purpose of Docker?

#51

Post by KaiserPro »

ageofwant wrote: post #20
KaiserPro wrote: post #13

docker and openVZ aim to do the same thing. docker is a glorified chroot and cgroup wrapper. There is also a library of prebuilt docker images (think of it as a tar of a chroot) and a library of automated build instructions. The library is the most compelling part of docker. everything else is basically a question of preference. You will hear a lot about build once, deploy anywhere. whilst true in theory, your mileag…

> docker and openVZ aim to do the same thing. docker is a process container not a system container. > docker is a glorified chroot and cgroup wrapper. that is fairly immaterial, suffice to say that the underlying linux core tech that enables docker has matured enough lately to enable a tool like docker. I built many containers and I never thought about them in terms of the underlying tech. > There is also a library o…

edit this sounds like I'm being petty, I apologise, I'm just typing fast.

> docker is a process container not a system container.

Valid. However the difference between docker image and openVZ images is the inclusion of an init system.

> Have to disagree here, primarily because each service should live in each own container, docker is a process container, not a system container. Assemble a system out of several containers, don't mash it all up into one - most people don't seem to get this about docker.

I understand your point,

I much prefer each service having an IP that is registered to DNS. This means that I can hit up service.datacenter.company.com and get a valid service. (using well tested dns load balancing and health checks to remove or re-order individual nodes)

Its wonderfully transparent and doesn't require a special custom service discovery in both the client and service. because like etcd it has the concept of scope you can find local instances trivially. using DCHP you can say connect servicename and let dhcpd set your scope for you.

> None is required. Containers are ephemeral and generally don't need to be migrated, they are simply destroyed and started where needed. Requiring 'hot migration' in the docker universe generally means you are doing it wrong. Not to say that there is no place for that.

This I have to disagree with you. For front end type applications, ones that hold no state, you are correct.

However for anything that requires shared state, or data its a bad thing. Take your standard database cluster ([no]SQL or whatever) of 5 machines. You are running at 80% capacity, and one of your hosts is starting to get overloaded. You can kill a node, start up a warm node on a fresh machine.

However now you are running at 100% capacity, and you now need to take some bandwidth to bring up a node to get back to 80%. Running extra machines for the purpose of allowing CPU load balancing aggrieves me.

I'm not advocating writing apps that cannot be restarted gracefully. I'm also not arguing against ephemeral containers, its more a case of easy load balancing, and disaster migration. Hot migration means that software is genuinely decoupled from the hardware.

Re: Ask HN: What is the actual purpose of Docker?

#53

Post by crdoconnor »

grhmc wrote: post #38
caw wrote: post #30

Earlier quoted context omitted.

How is building a Vagrant box via Ansible configuration any different than building a Docker container with a docker file? You can use both tools to build an image once and then rebuild for the updates. I don't see how the tool in any way violates that constraint. What is this rule to only build once? I can see not wanting to create multiple artifacts of your codebase, but with machines it is possible to continually…

> How is building a Vagrant box via Ansible configuration any different than building a Docker container with a docker file? Unless you're snapshotting that vagrant box and then deploying that to all your servers somehow, you are building multiple times. > What is this rule to only build once? I'd recommend reading the book Continuous Delivery. It is a fantastically helpful read. I prefer not to update my machines, b…

>Unless you're snapshotting that vagrant box and then deploying that to all your servers somehow, you are building multiple times.

You're also configuring many things in many different potentially complex ways.

The docker method of using environment variables as a configuration hack to get around this is pretty horrible, IMHO. Especially compared to ansible's YAML/jinja2 configuration.

Re: Ask HN: What is the actual purpose of Docker?

#54

Post by rahimnathwani »

ageofwant wrote: post #20
KaiserPro wrote: post #13

docker and openVZ aim to do the same thing. docker is a glorified chroot and cgroup wrapper. There is also a library of prebuilt docker images (think of it as a tar of a chroot) and a library of automated build instructions. The library is the most compelling part of docker. everything else is basically a question of preference. You will hear a lot about build once, deploy anywhere. whilst true in theory, your mileag…

> docker and openVZ aim to do the same thing. docker is a process container not a system container. > docker is a glorified chroot and cgroup wrapper. that is fairly immaterial, suffice to say that the underlying linux core tech that enables docker has matured enough lately to enable a tool like docker. I built many containers and I never thought about them in terms of the underlying tech. > There is also a library o…

"Assemble a system out of several containers, don't mash it all up into one - most people don't seem to get this about docker."

Care to elaborate on this? Do you use the linking system described here? https://docs.docker.com/userguide/dockerlinks/

I mean, your various containers still communicate over IP, right? Just a private IP network within the host, rather than outside?

(Obviously I've never used Docker.)

Re: Ask HN: What is the actual purpose of Docker?

#55

Post by tinco »

> What's the difference between Docker and normal virtualization technology (OpenVZ/KVM)? Are there any good examples of when and where to use Docker over something like OpenVZ?

Docker is exactly like OpenVZ. It became popular because they really emphasize their OpenVZ Application Templates feature, and made it much more user friendly.

So users of Docker, instead of following this guide: https://openvz.org/Application_Templates

They write a Dockerfile, which in a simple case might be:

    FROM nginx
    COPY index.html /usr/share/nginx/html
So no fuzzing with finding a VE somewhere, downloading it customizing it, and then installing stuff manually, stopping the container and tarring it, Docker does that all for you when you run `docker build`.

Then you can push your nice website container to the public registry, ssh to your machine and pull it from the registry. Of course you can have your own private registry (we do) so you can have proprietary docker containers that run your apps/sites.

From my perspective, the answer to your question would be: Always prefer Docker over OpenVZ, they are the same technology but Docker is easier to use.

But I've never really invested in OpenVZ so maybe there's some feature that Docker doesn't have.

Re: Ask HN: What is the actual purpose of Docker?

#56

Post by cpr »

rahimnathwani wrote: post #54
ageofwant wrote: post #20

Earlier quoted context omitted.

> docker and openVZ aim to do the same thing. docker is a process container not a system container. > docker is a glorified chroot and cgroup wrapper. that is fairly immaterial, suffice to say that the underlying linux core tech that enables docker has matured enough lately to enable a tool like docker. I built many containers and I never thought about them in terms of the underlying tech. > There is also a library o…

"Assemble a system out of several containers, don't mash it all up into one - most people don't seem to get this about docker." Care to elaborate on this? Do you use the linking system described here? https://docs.docker.com/userguide/dockerlinks/ I mean, your various containers still communicate over IP, right? Just a private IP network within the host, rather than outside? (Obviously I've never used Docker.)

The OP just means don't put everything into one container.

Re: Ask HN: What is the actual purpose of Docker?

#57

Post by patsplat »

bosse wrote: post #6
jacques_chester wrote: post #2

Docker uses the same kernel primitives as other container systems. But it tied together cgroups, namespaces and stackable filesystems into a simple cohesive model. Add in image registries and a decent CLI and the developer ergonomics are outstanding. Technologies only attract buzz when they're accessible to mainstream developers on a mainstream platform. The web didn't matter until it was on Windows. Virtualization w…

As an ops guy, I would also mention the benefits of the Dockerfile and docker-compose.yml, which could be clear sources for information to how the system is built, and which in most circumstances would build the same system in dev as in prod. By changing a docker tag in the configuration management, I can roll out a new version quite conveniently to staging and eventually to production. The potential minimalism of a…

Agreed.

Application runtime dependencies are a common source of communication breakdowns between development and infrastructure teams. Making the application container a maintained build file on the project improves this communication.

docker provides:

* a standard format for building container images (the Dockerfile)

* a series of optimizations for working with images and containers (immutable architecture etc).

* a community of pre-built images

* a marketplace of hosting providers

All at the cost of linux only, which is ok for many shops.

Re: Ask HN: What is the actual purpose of Docker?

#58

Post by SEJeff »

Kiro wrote: post #36

For me I don't understand the purpose at all. I have a few node.js and PHP services. Why do I need isolation and have them in containers? If I want an identical environment when developing I can use Vagrant.

FYI: Vagrant can use docker, rendering your argument invalid :)

http://docs.vagrantup.com/v2/provisioning/docker.html

Docker is about running isolated environments in reproducible ways. I get a container working just so on my desktop, ship it to an internal registry, where it gets pulled to run on dev and qa. It works identically to how it works on my desktop, then I ship it to production. One image that works the same on all environments. That is what docker was for, developer productivity.

Re: Ask HN: What is the actual purpose of Docker?

#59

Post by icebraining »

beat wrote: post #50
caw wrote: post #30

Earlier quoted context omitted.

How is building a Vagrant box via Ansible configuration any different than building a Docker container with a docker file? You can use both tools to build an image once and then rebuild for the updates. I don't see how the tool in any way violates that constraint. What is this rule to only build once? I can see not wanting to create multiple artifacts of your codebase, but with machines it is possible to continually…

First, not everything produces bitwise identical results from build to build (Websphere ear files, for example). Second, it's time consuming to rebuild from scratch every time. This is especially important if you're in a cloud environment and scaling horizontally for load. You want a way to bring resources online quickly.

All clouds I've used have snapshots - it's hard to get faster than creating a VM from one. You can just keep an up-to-date template using any config management tool.

Re: Ask HN: What is the actual purpose of Docker?

#60

Post by SEJeff »

jdoss wrote: post #37
justincormack wrote: post #8

OpenVZ is not upstream in the kernel; the container stuff that got merged is what Docker uses. Docker has much wider adoption than OpenVZ does now.

> Docker has much wider adoption than OpenVZ does now. I don't think your statement is true at this point in time. OpenVZ is used by a ton of companies in the hosting industry and by large companies such as Groupon and smaller ones like TravisCI [1]. I would't make a statement that that Docker has a wider adoption than OpenVZ at this point in time. Maybe in five years, yes it may have a wider adoption than OpenVZ. Op…

And Docker is massively used at Groupon, so your argument isn't valid.

https://engineering.groupon.com/2014/misc/dotci-and-docker/ http://www.meetup.com/Docker-Chicago/events/220936626/

Source: I work at 600 W Chicago, the Groupon World HQ, where they frequently host Docker meetups on the 6th floor.

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