What's wrong with that is that now your application--and, by extension, your developers--has (have) to care about a lot more stuff and needs to have its testing surface expanded appropriately. The potential interactions and therefore potential failures between, say, ops's cron jobs, the wire-up of stuff like logstash, changes to your chef configs, etc.means there's a ton more testing to be done. In a Docker world, the amount of stuff running in a context that the application can see is minimal and it's all related directly to the application in question. Your inputs and outputs can be clearly defined and this lets you present a stable API to the outside world (via volumes and links) while, as or even more importantly, providing a known-good, stripped-down environment for the application to run on. (chroot jails are a fine solution too, but I do prefer the relative handholding and easier application independence of Docker and AuFS.)
The other problem with your suggestion -- dd'ing and then running Chef or whatever -- is boot time. I can spin up an AMI ready to deploy Docker apps in under sixty seconds. We work in AWS, so I can't speak to the actual time of deploying a physical server, but I can download and deploy a Docker image from an AWS-hosted private registry in ten seconds. Chef won't even get its act together in thirty seconds, let alone do your stuff; between downloading a full VM disk image, the startup time for that virtual machine, and the time to run chef, you've wasted so much time.
Here at Localytics, we're trying to transition to an environment that is very comfortable with automatic scaling and can do so fast--seconds, rather than minutes--and Docker is a big part of that effort. Right now we deploy to AWS autoscaling groups (with AMIs defined via Packer). I'm pushing hard for us to use a clusterization system like Mesos/Deimos because it'll let us save money by introducing safe, sane multi-tenancy--and it'll let us react to changes in system load in mere seconds.
(obligatory: we're hiring. we work on fun stuff. eropple@localytics.com)
The other problem with your suggestion -- dd'ing and then running Chef or whatever -- is boot time. I can spin up an AMI ready to deploy Docker apps in under sixty seconds. We work in AWS, so I can't speak to the actual time of deploying a physical server, but I can download and deploy a Docker image from an AWS-hosted private registry in ten seconds. Chef won't even get its act together in thirty seconds, let alone do your stuff; between downloading a full VM disk image, the startup time for that virtual machine, and the time to run chef, you've wasted so much time.
Here at Localytics, we're trying to transition to an environment that is very comfortable with automatic scaling and can do so fast--seconds, rather than minutes--and Docker is a big part of that effort. Right now we deploy to AWS autoscaling groups (with AMIs defined via Packer). I'm pushing hard for us to use a clusterization system like Mesos/Deimos because it'll let us save money by introducing safe, sane multi-tenancy--and it'll let us react to changes in system load in mere seconds.
(obligatory: we're hiring. we work on fun stuff. eropple@localytics.com)