x-b3-sampled header is always set to 0 when accessing service through ingress controller
After few days of digging I've figured it out. Problem is in the format of the x-request-id header that nginx ingress controller uses.
Envoy proxy expects it to be an UUID (e.g. x-request-id: 3e21578f-cd04-9246-aa50-67188d790051) but ingrex controller passes it as a non-formatted random string (x-request-id: 60e82827a270070cfbda38c6f30f478a). When I pass properly formatted x-request-id header in the request to ingress controller its getting passed down to envoy proxy and request is getting sampled as expected. I also tried to removex-request-id header from the request from ingress controller to ServiceA with a simple EnvoyFilter. And it also works as expected. Envoy proxy generates a new x-request-id and request is getting traced.