PRs welcome. Most maintainers don't use tracing or metrics ourselves, so we need to lean on the community to contribute improvements.

I think this may be the reason Caddy doesn't work with grafana since they only expose the HTTPS port

I think this may be the reason Caddy doesn't work with grafana

Can you elaborate? In what way does Caddy "not work with grafana"?

When you create a free stack at grafana.com and try to set up their OTEL collector it recommends the following environment variables

export OTEL_EXPORTER_OTLP_PROTOCOL="http/protobuf"
export OTEL_EXPORTER_OTLP_ENDPOINT="https://otlp-gateway-prod-us-east-0.grafana.net/otlp"
export OTEL_EXPORTER_OTLP_HEADERS="Authorization=Basic SECRET"

I also added

export OTEL_EXPORTER_OTLP_TRACES_ENDPOINT="https://otlp-gateway-prod-us-east-0.grafana.net/otlp"

So problems with Caddy are

1. http/protobuf is the protocol required but as per the OP of this issue, it does not work because it's hard coded to GRPC tracer only. I tried to work around it with a change in my PR
2. The change unfortunately didn't work as somewhere else in the caddy codebase or one of it's imports it looks at the OTEL_EXPORTER_OTLP_ENDPOINT or OTEL_EXPORTER_OTLP_TRACES_ENDPOINT it parses the value and determines there's no port value (since grafana uses https which has a default port of 443 it doesn't place it)
3. Adding the port i.e. https://otlp-gateway-prod-us-east-0.grafana.net:443/otlp will make Caddy parse out the port as 443/otlp then there'd be an error saying port 443/otlp is not valid. I am unable to ascertain where that is in the code base

Maybe it's the way I am testing

RUN git clone https://github.com/trajano/caddy /mnt/
RUN xcaddy build \
    --replace github.com/caddyserver/caddy/v2/modules/caddyhttp/tracing=/mnt/modules/caddyhttp/tracing

FROM caddy
COPY --from=builder /usr/bin/caddy /usr/bin/caddy

Figured out what was wrong with the Dockerfile

Got a bit further but got

traces export: failed to send to https://otlp-gateway-prod-us-east-0.grafana.net/oltp/v1/traces: 404 Not Found

But posting directly using curl seems to work

Finally got it working, the last bit was a typo might've accidentally transposed two characters in the otlp in https://otlp-gateway-prod-us-east-0.grafana.net/otlp I see data in Grafana now with my PR.