Databricks Apps telemetry tables stay empty after following observability docs

[uniquejava]

A minimal reproduction repo is available here: https://github.com/uniquejava/mcp-server-hello-world

Problem

Databricks Apps telemetry target tables are created successfully, but they remain empty even after:

• enabling App telemetry
• deploying the app successfully
• configuring the app per the observability docs
• generating real traffic to the app

I reproduced this both with a custom app and with the official mcp-server-hello-world sample from this repo.

What I changed

For the official sample app, I only made the minimal observability changes from the docs:

• start command uses opentelemetry-instrument
• set OTEL_TRACES_SAMPLER=always_on
• add required OTel dependencies:
• opentelemetry-distro
• opentelemetry-exporter-otlp-proto-grpc
• opentelemetry-instrumentation-fastapi

What works

• app deploys successfully
• app is running
• app is reachable
• MCP endpoint works
• requests succeed (for example health)
• OTel packages are present in the app runtime

What does not work

These tables remain empty:

• workspace.demo.otel_logs
• workspace.demo.otel_metrics
• workspace.demo.otel_spans
• workspace.demo.otel_annotations

SELECT COUNT(*) FROM workspace.demo.otel_logs;
SELECT COUNT(*) FROM workspace.demo.otel_metrics;
SELECT COUNT(*) FROM workspace.demo.otel_spans;
SELECT COUNT(*) FROM workspace.demo.otel_annotations;

All return 0.

Additional checks

• target tables were created successfully
• target tables are Delta tables
• DESCRIBE DETAIL workspace.demo.otel_logs shows otel.schemaVersion = v2
• app Service Principal has USE CATALOG, USE SCHEMA, and table-level SELECT / MODIFY
• still no data appears

Why I think this is not app-specific

I first saw this in a custom MCP server app. To rule out app-specific causes, I repeated the experiment with the official sample app from this repo and
got the same result.

Questions

• Is this a known issue?
• Are there additional requirements not covered in the observability docs?
• Are there workspace / metastore / edition limitations for Databricks Apps telemetry?
• How can I verify whether the Databricks-managed telemetry ingestion pipeline is actually active for my app?

[uniquejava]

App overview

App logs

The app is receiving traffic successfully, but OpenTelemetry trace export is failing with:

Transient error StatusCode.UNAVAILABLE encountered while exporting traces to localhost:4314

This suggests the app is attempting to export telemetry, but the Databricks Apps local OTLP ingestion endpoint is not available or not accepting data in this environment. This may explain why the otel_* tables are created but remain empty.