Proposal: feature flag implementation for Juju

[John Meinel]

Given the constraints you just listed (globally set in the environment,
etc), why not just make it environment config, rather than yet-another-way
to set env config?

John
=:->


On Wed, Nov 26, 2014 at 5:22 AM, Tim Penhey <tim.penhey at canonical.com>
wrote:

> On 26/11/14 14:18, Andrew Wilkins wrote:
> > On Wed, Nov 26, 2014 at 6:47 AM, Tim Penhey <tim.penhey at canonical.com
> > <mailto:tim.penhey at canonical.com>> wrote:
> >
> >     Hi all,
> >
> >     There are often times when we want to hook up features for testing
> that
> >     we don't want exposed to the general user community.
> >
> >     In the past we have hooked things up in master, then when the release
> >     branch is made, we have had to go and change things there.  This is a
> >     terrible way to do it.
> >
> >     Here is my proposal:
> >
> >     http://reviews.vapour.ws/r/531/diff/#
> >
> >     We have an environment variable called JUJU_FEATURE_FLAGS. It
> contains
> >     comma delimited strings that are used as flags.
> >
> >     The value is read when the program initializes and is not mutable.
> >
> >     Simple checks can be used in the code:
> >
> >     if featureflag.Enabled("foo") {
> >       // do foo like things
> >     }
> >
> >     Thoughts and suggestions appreciated, but I don't want to have the
> >     bike-shedding go on too long.
> >
> >
> > I like the idea of having flags.
> >
> > I'm not sure about setting it at bootstrap and it being global. How
> > would we test upgrade scenarios where some agents have the feature, and
> > others don't?
>
> The idea is that the machines get the flags when they are deployed using
> environment variables in the upstart script (or other service starting
> thingimy-widget).
>
> All agents in a given environment would have the same flags.
>
> I'm in two minds about whether feature flags should be able to be turned
> on and off on the fly.
>
> I'm mostly against it as we may have different workers for feature
> flags, and this would mean that we'd then have to code watchers for the
> flags in order to start and stop workers based on flag changes.
>
> I think simple is better here.
>
> Tim
>
>
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