Nice, cool to hear flags in conjunction with canary releases.
Are your flags simply configuration stored in files that your applications read at runtime? Then you push those updates out with Salt?
Pretty much. Salt pushes out a supplemental config file that we use to build a php file (after merging with the defaults) with `define('FLAG_NAME_HERE', value);` that out core application reads at startup. We have different classes/roles for our boxes so we can roll out a flag to a specific type or some of a specific type if we are going to canary. I wouldn't say that our specific method is anything special but it works very well in practice.