Consider dropping support for protobuf 3 in opentelemetry-proto

[aabmass]

In #3070, we widened the supported version of protobuf to protobuf>=3.19, < 5.0 based on votes and discussion in #2880 (comment) and #3050

Long term, newer versions of protoc will not generate code that is compatible with older versions of protobuf library (see protocolbuffers/protobuf#11123 (comment)), meaning it will be hard to support both protobuf 3.x and 4.x. There are possible workarounds for this like

• generating code for both versions and choosing the correct one at runtime
• maintaining two major versions of opentelemetry-proto and making releases against both major versions with separate protoc compilers.

The alternative is to drop support for protobuf 3 altogether at some reasonable point in the future, say 6 months.

[iwedaz]

Another issue with Zipkin exporter:
https://github.com/open-telemetry/opentelemetry-python/blob/5a996fd9a4334c8f086b3cbea096f8feec6c15a2/exporter/opentelemetry-exporter-zipkin-proto-http/pyproject.toml

Please make the latest versions available.

[ocelotl]

@aabmass six months have passed, I think it is a good time to consider dropping support for protobuf 3

[daxartio]

Why should we drop support for protobuf 3? Maybe just add support for protobuf 4 in this package opentelemetry-exporter-zipkin-proto-http?

[aabmass]

@daxartio this issue was specifically regarding the opentelemetry-proto. The reason to drop protobuf 3 is so we can upgrade the version of protoc we use to generate the protobufs (newer versions of protoc don't work with protobuf 3 runtime library). If there is a separate issue with zipkin exporter, would you mind creating an issue for it?

[daxartio]

I don't mind that protobuf 3 will be dropped. But now i cannot use protobuf 4 because in the dependencies are written "protobuf ~= 3.12"

[aabmass]

@daxartio if you are specifically talking about the zipkin exporter, can you please create a separate issue for that. I agree that it is a problem.

[emdneto]

Closing as support for protobuf5 was merged (which drop support for protobuf 3 and 4) 🚀 #4206