Problem: FeatureFlag service calls to downstream PostgreSQL database aren't linked.
Reason: The reason for the missing downstream database link is that the current v1.0 release of Erlang/Elix OpentelemetryEcto instrumentation library doesn't yet add the OTel peer attributes net.peer.host and net.peer.port. These standardized attributes are used by Instana to correlate downstream services.
Solution: Although the instrumentation library provides other attributes with the downstream link details, it isn't possible to use plain OTel attributes for creating custom service mapping via manual service configuration. Therefore, in order to inject the required attributes into the generated spans it was necessary to modify the OpentelemetryEcto library source and use the custom-built library in place of the default distribution package.
The patched OpenTelemetryEcto library is available at https://github.com/styblope/opentelemetry_ecto. The rest of the solution involved changing the FeatureFlag service Elixir code dependencies and building a new custom image.
To demonstrate the context propagation across Instana and OTel tracing implementations, we chose to instrument the frontendproxy service with the Instana native tracer. The Instana sensor supports W3C propagation headers, which is the default propagation header format used by OpenTelemetry. We use a custom build of the Instana envoy sensor which supports W3C context propagation (public release of the W3C enabled sensor is due soon).