No application is that simple. You need services that persist between deployments. Like a database.

So you make the database run in it's own container and have the containers talk.

Now you want to upgrade the database. How do you do that?

So you have some persistent storage that can be attached to the containers.

Now you create a new container that has all the exact knowledge (in the form of ad-hoc scripts?) that it's job is to get the attached volume and upgrade the data there and then run the new version of the database?

How is that more convenient or in any way better than chef or puppet?

Also, there is no real animosity or conflicting choice between Chef/Puppet and Docker. While there's overlap, there's nothing preventing you from taking the best of both technologies and integrating them. In fact, there are projects (like deis.io) which attempt to do just that.

I have written about how to do basic data migrations with Docker. You can find the link in my profile.

Also I completely agree that data migrations are tricky, that's why I need a tool to help me there as best as possible.

I should have asked: Given that I'm familiar with or can learn Chef/Puppet what advantage do I get from (also) using Docker. Or what advantage will I get down the road from (also) using Docker?

For example limiting resources come to mind, giving the processes in the container different IO priorities, memory allowances etc. But that's all just cgroup settings, I can do that without creating a container (via Docker) for individual processes.

I just don't see any situation where a Docker container is more useful than a Chef/Puppet recipe. And for any "complicated" setup I feel the advanced features of Chef/Puppet that allow me to fine-tune the setup for each deployment make up for the ease of use of Docker.

Yet there's a huge amount of buzz around Docker and containerization in general. What am I missing?

Chef/Puppet don't solve the problem of running multiple apps with conflicting dependencies on the same machine. A docker image is kinda of like a more efficient virtual machine in that it isolates containers from each other. Maybe you're running 15 containers on one machine each running various different versions of rails, or whatever.

Chef/Puppet let you automate the setup of a machine so you can duplicate it; a docker image basically is a machine you just copy around, and like a VM, they're their own little worlds (for the most part).

That's my understanding anyway.

My view on this, basically, is that the role of automation tools in the Docker realm is going to be exactly like it is with most of the people who like to 'treat cloud like cloud' -- i.e. immutable services.

The config management tools -- whether Ansible, Puppet, Chef, Ansible, whatever -- are a great way to define the nature of your container and have a more efficient description of it.

You'll also continue to use management software to set up the underlying environment.

And you might use some to orchestrate controls on top, but the set of management services to manage docker at a wider scale are still growing in nature and very new.

I'm keeping an eye on things like shipyard but expecting we'll see some more companies emerge in this space that provide management software on top.

Is Docker right for everyone? Probably not. However I like how it is sort of (in a way) taking the lightweight vagrant style model and showing an avenue to which software developed in that way can be brought into production, and the filesystem stuff is pretty clever.

Hi, I'm the creator of Docker. You are not the only one asking this question :) Here's a discussion on the topic between me and the author of a fairly critical blog post titled "docker vs reality: 0-1", which should give you an idea of his state of mind :) I left a comment at the end.

http://www.krisbuytaert.be/blog/docker-vs-reality-0-1

I wrote a blog post about Docker and Configuration Management that elaborates on this:

http://kartar.net/2013/11/docker-and-configuration-managemen...

And I wrote a blog post talking about using Puppet and Docker that talks about how they might interact:

http://kartar.net/2013/12/building-puppet-apps-inside-docker...

Dependency management without having the high(er) cost of full VMs.

How do you upgrade the database usually? You can also do it the same way.

Not saying it really solves all the problems, just that it solves some of them.

Lots of people go years without upgrading the database that "shipped" with their application! As well, I know of many enterprise applications that literally ship with an entire _server_ as their method of production. You literally buy a server! Containers seem better than that.

They definitely aren't to be used for everything. I wouldn't use them in your situation at all - but they work well for many other things.

What about in a dev environment? It seems that configuration on a single local host would look vastly different, in spite of the same code running.

http://docs.docker.io/en/latest/examples/running_redis_servi...

It shows how a container can be "linked" to another container with an alias, and that alias then causes environment variables within the container to point to the correct IP address and port:

    DB_NAME=/violet_wolf/db
    DB_PORT_6379_TCP_PORT=6379
    DB_PORT=tcp://172.17.0.33:6379
    DB_PORT_6379_TCP=tcp://172.17.0.33:6379
    DB_PORT_6379_TCP_ADDR=172.17.0.33
    DB_PORT_6379_TCP_PROTO=tcp