I'm not totally sure whether this is a bug in cowboy_telemetry or in the way the telemetry events are use by opentelemetry_cowboy.
telemetry:execute seems to have the assumption the all events send from a process belong to the same request or span.
The way cowboy handles HTTP/2 and invokes it stream handlers results in a violation of that assumption.
cowboy uses a single process for each TCP connection. All stream handlers will be invoked from that process. However, a single HTTP/2 connection can have multiple HTTP/2 streams. That means that events from different HTTP/2 requests can all be invoked from the same process. Requests on different HTTP/2 streams are not synchronized. That can result in interleaving calls to telemetry:execute.
The interleaving might not be a problem for metrics. But when the requests are used to start and stop tracing spans with only the information from the process itself, this will go wrong.
I'm not totally sure whether this is a bug in cowboy_telemetry or in the way the telemetry events are use by opentelemetry_cowboy.
telemetry:executeseems to have the assumption the all events send from a process belong to the same request or span.The way cowboy handles HTTP/2 and invokes it stream handlers results in a violation of that assumption.
cowboy uses a single process for each TCP connection. All stream handlers will be invoked from that process. However, a single HTTP/2 connection can have multiple HTTP/2 streams. That means that events from different HTTP/2 requests can all be invoked from the same process. Requests on different HTTP/2 streams are not synchronized. That can result in interleaving calls to
telemetry:execute.The interleaving might not be a problem for metrics. But when the requests are used to start and stop tracing spans with only the information from the process itself, this will go wrong.