I’m trying to use OpenTelemetry auto-instrumentation in Deno with the following environment variables:

OTEL_DENO=true
OTEL_EXPORTER_OTLP_ENDPOINT=
OTEL_SERVICE_NAME=service-1-development
OTEL_METRIC_EXPORT_INTERVAL=10000

I'm running my Deno server with the --unstable-otel flag.

The OpenTelemetry Collector is running as a Docker container on a remote system and is exposed via a Cloudflare Tunnel, which forwards traffic to http://otel-connector:4318.

If I manually test the endpoint using curl or a browser, I get a 404 page not found, which indicates that the connection itself is working. The tunnel is currently not protected by authentication.

However, when I start my Deno server and send a request, I receive the following error in the logs after a few seconds:

name="BatchSpanProcessor.Flush.ExportError" reason="Other(hyper_util::client::legacy::Error(Connect, ConnectError(\"tcp connect error\", Os { code: 61, kind: ConnectionRefused, message: \"Connection refused\" })))" message=Failed during the export process

Here is my OpenTelemetry Collector configuration (otel-connector-config.yaml):

receivers:
  otlp:
    protocols:
      http:
        endpoint: ":4318"
        cors:
          allowed_origins:

processors:
  batch:
    timeout: 1s
    send_batch_size: 1024

exporters:
  otlphttp:
    endpoint: "http://loki:3100/otlp"

service:
  telemetry:
    logs:
      level: "debug" 
  pipelines:
    logs:
      receivers: [otlp]
      processors: [batch]
      exporters: [otlphttp]

Things I've tried:

• Setting endpoint: 0.0.0.0:4318 in the OTEL Collector config
• Using localhost:4318 instead of otel-connector:4318
• Adding allowed_origins explicitly and leaving it empty

None of these changes have resolved the issue.

Question: What could be causing this Connection refused error? Am I missing any configuration steps to make OpenTelemetry auto-instrumentation work with Deno?

Thanks in advance for any help!