Activator: the route rule for each inactive revision should have its own appendHeaders field

[akyyy]

/area autoscale

/kind dev
/kind doc

Expected Behavior

The ideal solution is to append different revision name as headers for each inactive revision.

Actual Behavior

I opened a feature request for Istio. istio/old_issues_repo#332.
Since appendHeaders is a field for RouteRule Spec, we don't have that granularity. We will direct traffic for all inactive revisions to activator service; and the activator will send the request to the inactive revision with the largest traffic weight. The consequence of using appendHeaders at Spec is: if there are more than one inactive revisions, the traffic split percentage would be distorted in a short period of time.

[akyyy]

Corresponding code is here:
https://github.com/elafros/elafros/blob/e2f88af1bb854c2fa4562d978fcb3d63d3757352/pkg/controller/route/ela_istio_route.go#L52

[mattmoor]

/assign @tcnghia

Will v1alpha3 fix this?

[tcnghia]

It looks like v1alpha3 won't fix it as is. The appendHeaders is still a route parameter, not a destination parameter.

We could change this by making the revision-service a virtual host, but it may require extra an extra hop. The main route will need to route through ingress gateway.

[mattmoor]

I think this is enabled by Istio 1.1, whether that lands for 0.3 is a good question.

[k4leung4]

/area networking