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Ask HN: What is the actual purpose of Docker?

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Ask HN: What is the actual purpose of Docker?

#1

Post by someguy1233 »

I'm hearing about Docker every other day, but when I look into it, I don't understand the purpose of it.

I run many websites/applications that need isolation from each other on a single server, but I just use the pretty-standard OpenVZ containers to deal with that (yes I know I could use KVM servers instead, but I haven't ran into any issues with VZ so far).

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?

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

#2

Post by jacques_chester »

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 was irrelevant until it reached x86, containerization was irrelevant until it reached Linux.

Disclaimer: I work for a company, Pivotal, which has a more-than-passing interest in containers. I did a presentation on the history which you might find interesting: http://livestre.am/54NLn

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

#6

Post by bosse »

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 container is also an important concept to mention, with fast startup-times and less services that could potentially be vulnerable.

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

#7

Post by grhmc »

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 that Docker solves, and in such a way that developers can do most of the dependency wrangling for me. I don't even mind Java anymore because the CLASSPATHs can be figured out once, documented in the Dockerfile in a repeatable programatic fashion, and then ignored.

In my opinion the rest of it is gravy. Nice tasty gravy, but I don't care so much about the rest at the moment.

Edit: As danesparz points out, nobody has mentioned immutable architecture. This is what we do at Clarify.io. See also: https://news.ycombinator.com/item?id=9845255

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

#10

Post by odiroot »

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?

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