Adds support for zipkin v2

[jcchavezs]

Do you want to request a feature or report a bug?

Feature

What did you expect to see?

Currently Traefik only supports zipkin v1 by using zipkin-go-opentracing v0.3.x. This is because it uses the old version of zipkin-go-opentracing which only supported v1 reporting. Version 0.4.2 of zipkin-go-opentracing uses zipkin v2 format which is smaller and the default reporting format (read this to understand how v2 is better than v1).

We have two options here:

1. We move to new version of zipkin-go-opentracing and reports in v2 format, meaning that users will need to change their reporter URL from :host/api/v1/spans into :host/api/v2/spans. Feels like a breaking change but there is nothing else users will need to do.
2. We maintain both versions of zipkin-go-opentracing, this is weird because basically we might need to maintain both versions of zipkin-go-opentracing: 0.3 for v1 and 0.4 for v2 but go modules support that. This will require for us to find a way in configuration to determine if v1 or v2, it can be another parameter but then it feels odd as the httpEndpoint is different depending on v1 or v2.

Personally I would go for 1 but I would like to hear other's opinion. I am happy to come up with a PR for this.

Ping @adriancole @basvanbeek

[jbdoumenjou]

Hi @jcchavezs,

It doesn't seem possible to use go modules to keep both versions of zipkin-go-opentracing, unless you have specific idea.
Anyway, we think it is reasonable to migrate to the v2 version and stop the support of the v1.

[basvanbeek]

That is correct. You need to either pick a V1 old style release < 0.4.0 or pick a v2 bridge release 0.4.x.
The 0.4.3 release is the best minimum release to start from.

[jcchavezs]

Interesting. I thought we could do it as explained in here for example: https://www.melvinvivas.com/go-version-1-11-modules/ but I haven't done it yet. My specific idea was to create another package for zipkin-v2 and decide accordingly to config, however I am really happy we can just migrate to the new version. I will see if I can work on that today.

[ldez]

To use 2 versions, the 2 versions must be 2 different major versions (semver).

[traefiker]

Closed by #5283.