The benefits of containerization are not limited to production deployment. Docker makes it trivial to run the exact same container in QA/dev as well - it's a 10 line Dockerfile and three commands (create, build, run) vs having to build custom shell/python scripts. Don't underestimate how useful that is, especially in smaller offices where you don't have the staff dedicated to automating everything. Even small shops also benefit from the ephemeral nature of containers - redeploying a container is a lot quicker and easier than redeploying an entire VM/physical server. PaaS isn't without it's own issues either (you have to learn the AWS/Google/openShift/azure/heroku way of doing things) and can be cost prohibitive.
What does Docker bring to this? This is basically the argument "use your production deployment mechanism to create your development environment". There are lots of ways other than Docker to do this, Vagrant being one of the most prominent.
One of the differences between a containerized deployment and scripted provisioning with tools like Vagrant is the state of a node following a deployment failure.
Deployment of a container to a node is roughly an atomic transaction. If it fails due to a network partition or server crash etc. The container can just be deployed again to the node again. By comparison, a partially executed provisioning script can leave the target node in an arbitrary state and what needs to happen next to bring the node online depends on when and how the deployment script failed as well as the nature of any partial deployment...and whatever state the server was in prior to deployment.
That's a reason why Docker is great for production deployment. If you don't use Docker for production your production deployment scripts have to deal with that.
But if you use your production deployment scripts for development deployments, then that problem has been dealt with one way or another.
Absolutely. One can reinvent any part of the Docker [+ GKE] setup from first principles on either dev or prod axis. That being said, it's nice to spend a day to setup Docker [+ GKE], and have [most of] the "babysit apt-get" and "babysit prod runtimes" taken care for.
Not being a containerization user currently, I cannot vouch for the accuracy of the above assertions, but this reasoning is why I've been pondering moving from VMs to containers at or consultancy. We regularly have to "approximate" customer setups for development, and distributing an environment definition to peer developers seems more appropriate than the umpteenth VM clone.
I can very much recommend that approach. Working in a very small team we're using docker solely for reproducible development environments with very small footprint. Our projects are usually smaller low range backoffice sites.
We're still hesitant to deploy docker in production though, but its on our list. For now we rebuild the production environment from the recipes in the Dockerfile and docker-compose.yml.
Before that we were using VMs with vagrant. I never really liked how ressource intensive and slow they where. And without VM I also don't see the need for Vagrant anymore if I can use docker directly.
So after 2 years of using docker I'm really very happy with our development setup.
It's just adding yet another layer to the stack, so another interface to learn. And if things don't work you have to deal with the “low level“ docker setup anyway.
Seriously, I've never looked back at Vagrant ever since.
