[FEATURE] Change `fractional` custom op from percentage-based to relative weighting.

[toddbaert]

Requirements

Currently, the fractional operator is percentage-based; meaning you must specify the relative distribution of the variants in terms of a percentage. I believe we should change this instead to be a relative weight, meaning that the integers do not need to sum to 100. For example, this fractional:

"fractional": [
          [
            "red",
            25
          ],
          [
            "blue",
            25
          ],
          [
            "green",
            25
          ],
          [
            "grey",
            25
          ]
        ]

Would remain valid, but could also be expressed as:

"fractional": [
          [
            "red",
            1
          ],
          [
            "blue",
            1
          ],
          [
            "green",
            1
          ],
          [
            "grey",
            1
          ]
        ]

We could even make the number in the bucket optional, so that an even split would be assumed if none was provided (we could simply default to 1).

Benefits:

• adding new buckets becomes easy, there's no need to alter previous buckets
• supports much finer targeting
  • clear and consistent support across implementations for targeting finer than a single percentage (I don't believe all impls currently support non-integer distributions)
  • easy a clear support for fractions that aren't factors of 100 (1/1/1 vs 33/33/34)
• non breaking (current percentage based rules will still work)

Challenges:

• we should specify max values for the integers, and perhaps a max array length for the bucket array

If there's a general consensus to this, I will create some child issues in the relevant repositories and use this issue as the parent "tracking" issue.

[Kavindu-Dodan]

+1 I think this is a good new (non-breaking) feature

[colebaileygit]

Regarding default weights, I think it'd be cleanest to allow specifying strings directly in place of arrays. Though this does become incompatible with the shorthand syntax which relies on string/arr type checking.

Overall I like having the relative weighting syntax available even without the optionality of traffic weights

[agardnerIT]

We did this with Keptn and it was never understood by users. So I'm not in favour as it seems to add complexity where there doesn't need to be any.

What would be nice (and perhaps this achieves this) is the ability to quickly say: 25% to red and the rest (implicitly) 75% to the default:

"defaultValue": "blue",
"fractional": [
          [
            "red",
            25
          ],
]

[colebaileygit]

@agardnerIT How would you support 3-way experiments with 33.3% traffic share, or any non-integer traffic share then?

Should we allow floats or strings in addition to integer?

[beeme1mr]

I think we should likely stick to integers only. What would be the use case for floats or strings?

I also don't think this complicates the configuration. In my opinion, it would make the configuration simpler and more flexible. It is also non-breaking, so the old way would continue to work.

[bacherfl]

@toddbaert If still available, I would like to work on this one :)