But it works on my machine!

Reading time ~2 minutes

Don’t let “it works on my machine” be a thing!

It’s convenient to just git pull a project, install some dependencies and get on with development. But that doesn’t work well enough, even with runtime version managers like ruby’s RVM and python’s virtualenv , to be reliable. You may be able to control the runtime environment but what about all the binary dependencies?

And so technologies like vagrant with virtualbox and now docker , have transformed one-off snowflakey development environments into virtualised sandboxes that can be brought up and down as we hop from project to project without dependency versioning tripping anyone up.

But then you have to consider the differences between development and production environments.

Docker allows container images to be (almost) identical between development and production, which is the ideal. But a vagrant+virtualbox workflow, which we use at my workplace due to limitations with Amazon’s ECS is dangerous without a means of keeping development in sync with production. The solution is to base vagrant and EC2 images on the same version of linux and then to provision both types of environment using the same definition, for example using chef cookbooks.

Of course a development environment will probably contain ‘extra’ stuff, for example database servers that are externalised on the production platform (e.g. by using RDS), in which case keeping the versions consistent becomes an easily-solved issue within the cookbooks. Again, docker provides a more elegant solution with its support (especially via docker-compose) for multi-container deployments.

How can you share your chef configuration between vagrant and AWS EC2? It used to be difficult/a hack, but the vagrant-aws plugin makes life easier. It’s not perfect since the EC2 instances created by one developer end up being private to him and not able to be managed by other developers, but bringing up new instances instead of updating existing ones is a best practice anyway so that’s not a real blocker.

But the Hashicorp folks, who own Vagrant, are rolling out a reallt interesting and rather complete suite of tools that appear to wrap up all these concerns and much more. The part of the jigsaw that solves the problem of sharing development and production platform builds is the concern of their Packer product. While the end-to-end solution includes Terraform to build AWS infrastructures, as well as more tools to deal with secrets management, service orchestration and scheduling that I’m very interested to look at for the future.

Finally, to reiterate… don’t let ‘required’ tools or dependencies creep onto developers’ laptops outside of your virtualised and controlled development environments. Because then you’re back to “it works on my machine”. If there are tools required that are shared between projects or that are difficult to install inside project environments then make a sandbox (container or VM) specifically for the tool.

Don’t be satisfied with “OK let’s make sure everyone does brew install foo” because you’ll end up in a world of “it doesn’t work anywhere except my machine”.

AWS does Container Deployment Automation

I talked about some adventures in the land of[Docker](https://www.docker.com/)a few weeks ago, in[Docker is an Immature Technology on AWS...… Continue reading

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