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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?

#11

Post by omarforgotpwd »

odiroot wrote: post #10
grhmc wrote: post #7

For me, it is the ultimate in the idea in Continuous Delivery of "build once." I can be very confident that the docker image I build in the first stage of my pipeline will operate correctly in production. This is because that identical image was used for unit tests, to integration and functional testing, to the staging environment and finally production. There is no difference than configuration. This is the core tha…

How do you handle different configurations then? Especially if you need to provide N values (or structured data). Also, how do you manage your containers in production?

I use environment variables, which can be passed in as arguments when you start the container. In cases where the configuration is complicated I'll use an environment variable to tell the container which redis key / db key to load config from.

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

#12

Post by magicmu »

grhmc wrote: post #7

For me, it is the ultimate in the idea in Continuous Delivery of "build once." I can be very confident that the docker image I build in the first stage of my pipeline will operate correctly in production. This is because that identical image was used for unit tests, to integration and functional testing, to the staging environment and finally production. There is no difference than configuration. This is the core tha…

Like OP, I've been wondering exactly what problem Docker is meant to solve -- thank you for this explanation, it makes total sense.

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

#13

Post by KaiserPro »

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 mileage will vary.

what docker is currently good for:

o micro-services that talk on a messaging queue

o supporting a dev environment

o build system hosts

However if you wish to assign ip addresses to each service, docker is not really mature enough for that. Yes its possible, but not very nice. You're better off looking at KVM or vmware.

There is also no easy hot migration. So there is no real solution for HA clustering of non-HA images. (once again possible, but not without lots of lifting, Vmware provides it with a couple of clicks.)

Basically docker is an attempt at creating a traditional unix mainframe system (not that this was the intention) A large lump of processors and storage that is controlled by a singular CPU scheduler.

However, true HA clustering isn't easy. Fleet et al force the application to deal with hardware failures, whereas Vmware and KVm handle it in the hypervisor.

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

#14

Post by alextgordon »

1. Stateless servers. Put your code and configuration in git repos, then mount them as volumes in your docker container. The absolute star feature of docker is being able to mount a file from the host to the container.

You can tear down the host server, then recreate it with not much more than a `git clone` and `docker run`.

2. Precise test environment. I can mirror my entire production environment onto my laptop. No internet connection required! You can be on a train, on a plane, on the beach, in a log cabin in the woods, and have a complete testing environment available.

Docker is not a security technology. You still need to run each service on a separate host kernel, if you want them to be properly isolated.

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

#15

Post by mbrock »

I don't know much about virtualization technology, but Docker is nice for me because it's an accessible, well-known, and rather easy way to make applications easy and straightforward to run.

Where I've worked in the past, setting up a new development or production environment has been difficult and relied on half-documented steps, semi-maintained shell scripts, and so on. With a simple setup of a Dockerfile and a Makefile, projects can be booted by installing one program (Docker) and running "make".

You could do that with other tools as well, but Docker, and even moreso the emerging "standards" for container specification, seems like an excellent starting point.

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

#18

Post by crdoconnor »

grhmc wrote: post #7

For me, it is the ultimate in the idea in Continuous Delivery of "build once." I can be very confident that the docker image I build in the first stage of my pipeline will operate correctly in production. This is because that identical image was used for unit tests, to integration and functional testing, to the staging environment and finally production. There is no difference than configuration. This is the core tha…

I get this by using vagrant + ansible rather than docker. Easy to spin up or destroy the environment in the same way in a VM, staging server or live environment.

I don't really see the point of lightweight virtualization. It provides an illusion of isolation which will likely come crashing down at some probably very inconvenient point (e.g. when you discover a bug caused by a different version of glibc or a different kernel).

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

#19

Post by mariocesar »

The most common pro is "Build once deploy everywhere" even is possible, I always feel pushing a 500 MB tar image to the production servers is more an annoyance than being helpful; Yes, You can setup your own registry but maintaining the service, securing, adding user permissions and maybe use a proper backend like S3 is an extra annoying layer and another component that could fail.

If the docker tool will have something like `docker serve` and start his own local registry will be more than great.

For this case when I switch to Go was a great solution, building the binary is everything you need.

About docker being helpful for development, definitively yes, I switch to postgres, elasticsearch and redis containers instead of installing them on my computer, is easy to flush and restart and having different versions of services is also more manageable

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

#20

Post by ageofwant »

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 of prebuilt docker images (think of it as a tar of a chroot)

yes

> and a library of automated build instructions

more accurate to say there is a well defined SDL for defining containers.

> You will hear a lot about build once, deploy anywhere. whilst true in theory, your mileage will vary.

have to agree, this is oversold as most of the config lives in attached volumes and needs to be managed outside of the container.

> However if you wish to assign ip addresses to each service, docker is not really mature enough for that. Yes its possible, but not very nice. You're better off looking at KVM or vmware.

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.

> There is also no easy hot migration. So there is no real solution for HA clustering of non-HA images. (once again possible, but not without lots of lifting, Vmware provides it with a couple of clicks.)

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.

As a final note, all my docker hosts are kvm vm's.

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