Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Ask HN: Why use Docker and what are the business cases for using it?

news.ycombinator.com

Post reply on HN
Print view View original

41–50 of 137 posts

Re: Ask HN: Why use Docker and what are the business cases for using it?

#41

Post by bacheson1293 »

rcconf wrote: post #38

My apologies if I'm hijacking the original poster. Does Docker handle multi-environment configuration management? For example: qa, stage and live have the same config files, but different values. Currently we're using Ansible and we set variables for a specific environment, then we feed those variables into config files based on where we're deploying to (config files are not duplicated, only variables that feed into…

Absolutely. This situation is handled by using Environment variables. Depending on the environment, I use environment variables to point services at different places (ie dedicated production database server vs my micro dev mysql container).

Re: Ask HN: Why use Docker and what are the business cases for using it?

#42

Post by rlpb »

e40 wrote: post #39

Say you're running on CentOS 6.6 (or the equivalent RHEL) and you want to run some software that won't work because you need a newer library than is installed (this recently happened to me recently trying to install Transmission). You have two choices: 1. Upgrade to CentOS 7.x. 2. Use Docker and install the software into a container using a newer OS (CentOS 7.x or a newer Debian). #1 is very expensive and sometimes i…

Isn't that a business case for containers, rather than Docker specifically? If you want to install an entire OS into a container, LXD is more suitable, surely?

Re: Ask HN: Why use Docker and what are the business cases for using it?

#43

Post by geerlingguy »

rcconf wrote: post #38

My apologies if I'm hijacking the original poster. Does Docker handle multi-environment configuration management? For example: qa, stage and live have the same config files, but different values. Currently we're using Ansible and we set variables for a specific environment, then we feed those variables into config files based on where we're deploying to (config files are not duplicated, only variables that feed into…

One way I've seen many people tackle this problem is to have the Dockerfile/image built in a more generic way, then the end of the Dockerfile kicks off an Ansible playbook (or some other lite CM tool) that will configure everything for the proper environment (e.g. change configuration and kick off a service, something along those lines).

Some will even go as far as using a CM tool to do the entire internal Dockerfile build, and the Dockerfile is just a wrapper around the CM tool. This does require more bloat inside the Docker image, as you need to have your CM tool or whatever other supporting files/scripts installed in the image, but it does make more complex scenarios much simpler.

Re: Ask HN: Why use Docker and what are the business cases for using it?

#44

Post by osipov »

rcconf wrote: post #38

My apologies if I'm hijacking the original poster. Does Docker handle multi-environment configuration management? For example: qa, stage and live have the same config files, but different values. Currently we're using Ansible and we set variables for a specific environment, then we feed those variables into config files based on where we're deploying to (config files are not duplicated, only variables that feed into…

This is not necessarily a part of the Docker specification, but here's a best practice followed by many apps running in Docker containers: http://12factor.net/config

Re: Ask HN: Why use Docker and what are the business cases for using it?

#45

Post by ninkendo »

jgrowl wrote: post #34

Besides just actually running software, I also find it really neat when projects use docker to build their entire application. It provides an effective means of documenting all of your dependencies and making reproducible builds. Take the docker-compose for example. You can just check the code out, run a single script that builds the project for your environment and everything is pretty much self contained in the doc…

A docker file is a pretty poor way of providing reproducible builds though.

First off there's the FROM line, which can contain whatever opaque image you feel like that already has dependencies inside it, and who knows how they got there or what will happen when it needs to be updated.

Then there's the fact that it's like a script but worse: every line creates a new image, and docker will try to cache the results after each line, but that cache can work against you if you're not really careful (imagine if build systems like make worked that way? No dependency tree, just refusing to execute the first half of your makefile because well, it worked last time so why do it again?

And in practice, you get to find out how many people just put an "apt-get update" in their docker file too. Now our backwards compatiblility is really just equal to Debian's. Hope there's no back ports repos in there or anything that would give a non-backwards-compatible package!

It's certainly possible to use Dockerfiles to create reproducible builds, but it's literally no better than a shell script at doing that. You have all the rope you need to hang yourself and then some.

Re: Ask HN: Why use Docker and what are the business cases for using it?

#46

Post by falcolas »

bacheson1293 wrote: post #41
rcconf wrote: post #38

My apologies if I'm hijacking the original poster. Does Docker handle multi-environment configuration management? For example: qa, stage and live have the same config files, but different values. Currently we're using Ansible and we set variables for a specific environment, then we feed those variables into config files based on where we're deploying to (config files are not duplicated, only variables that feed into…

Absolutely. This situation is handled by using Environment variables. Depending on the environment, I use environment variables to point services at different places (ie dedicated production database server vs my micro dev mysql container).

Remember that environment variables are visible to processes outside the container (i.e. users), if they have the same or higher privileged user. They are not a great place to store passwords or any other confidential information.

Re: Ask HN: Why use Docker and what are the business cases for using it?

#47

Post by davexunit »

jgrowl wrote: post #34

Besides just actually running software, I also find it really neat when projects use docker to build their entire application. It provides an effective means of documenting all of your dependencies and making reproducible builds. Take the docker-compose for example. You can just check the code out, run a single script that builds the project for your environment and everything is pretty much self contained in the doc…

>making reproducible builds.

Docker builds actually aren't reproducible. There are many sources of non-determinism that Docker cannot address. Do you use the base images from DockerHub as-is or do you run 'apt-get upgrade' or whatever for security patches? If you do, the result you get from building that image (as opposed to using what's in a cache) is different depending on the time it was built. The same goes for any Dockerfiles that compile from source. Hell, just extracting a source tarball results in a different hash of the source tree because of the timestamps on the files. You and I have little hope of building the same image and getting the same exact result.

Build reproducibility is a very interesting topic with some unsolved issues, but Docker isn't helping with it. See https://reproducible.debian.net for a good resource about build reproducibility.

Re: Ask HN: Why use Docker and what are the business cases for using it?

#48

Post by yebyen »

rubiquity wrote: post #18
rehevkor5 wrote: post #7

Have you ever used provisioning software like Chef to prepare a server to run your software? Have you ever used that in conjunction with Vagrant in order to test out your provisioning and software deployment locally? Docker replaces (or can replace) all of that.

Docker does NOT replace configuration management tools like Chef, Puppet and Ansible. Those are still necessary for preparing the host machine which Docker containers will run on. Where Docker does alleviate/reallocate some things is in the configuration of the containers that run on those hosts. Instead of configuring the host for Ruby/Python/etc. you would move that configuration to your Dockerfile. But I think CM…

> Chef, Puppet and Ansible. Those are still necessary for preparing the host machine

In many cases now, they are not. Docker containers can run on CoreOS, which machines are designed to be configured entirely from a cloud-config file, organized in clusters.

With Deis for example, you can build and orchestrate your scalable web service in Docker containers without even writing a Dockerfile, or necessarily knowing anything about how the Docker container is built. The builder creates slugs with the necessary binaries to host your service, and you tell the container how to run itself with a (often one-line) Procfile.

I would still want chef scripts for my database server, but for things that can live in a container on a Fleet cluster, I most certainly do not use Chef, but I absolutely do get reproducible hands-off builds for my runtime environment, and without spending time individually preparing the host machines.

Re: Ask HN: Why use Docker and what are the business cases for using it?

#49

Post by rlpb »

Docker, or containers in general? I'd really like to hear about Docker specifically, but most of the answers so far seem to relate to containers in general, rather than Docker specifically.

What are the business cases for using Docker over some other container-based solution?

Re: Ask HN: Why use Docker and what are the business cases for using it?

#50

Post by deftek »

dmarg wrote: post #12
scraymer wrote: post #10

Maybe you have looked already and it wasn't useful to you but on the Docker website it has some pretty good marketing to explain its usefulness: https://www.docker.com/whatisdocker Why Use Docker: "How does this help you build better software? When your app is in Docker containers, you don’t have to worry about setting up and maintaining different environments or different tooling for each language. Focus on creating…

Yeah, I looked at the Docker website. I feel that Docker is super good at marketing and wanted to get some other opinions.

Here is CoreOS opinion on docker:

https://coreos.com/blog/rocket/

Post reply on HN