Juju relations - where's my data?

[Matthew Wedgwood]

On 06/05/2013 03:52 PM, Gustavo Niemeyer wrote:
> That's a great post Matthew, thanks for sharing it!
> 
> A minor note on the first model:
> 
>     "The model holds as long as you have only one unit in each related service.
>     You write from one unit and read from the other, and everything seems
>     consistent. The consistency breaks when you add a second unit in one of
>     the related services."
> 
> The single bucket actually fails even if you have just a single pair
> of units. How would the two units exchange an ip address under the
> same setting name, for example?

I didn't really try to call out all the holes in the first two models. The second model has the same problem.

The main thing I wanted to get across was that charmers (including myself) will conceive a mental model of relations that, although inconsistent, roughly fits the behavior they see. Going into charming, I thought relation-get and relation-set were two sides of the same coin and tried to conjure up a story that fit that expectation. Figuring out that they're actually two sides of two *different* coins was a key realization to understanding relations.

-Matthew