Deno Open Telemetry data to a simple file log

[acrodrig]

I have a project where having a grafana server is overkill, but I still would like to have all the OTEL data collected go to a file (per day for example).

Is this possible without writing (much) code? How would I go about? I googled, I asked the LLM powers that be, and I have not been able to formulate an answer for myself.

Thanks.

[anntnzrb]

Deno's OTEL only exports to OTLP endpoints, not files directly. Create a minimal HTTP server (~15 lines) that receives OTLP JSON and writes to files:

const data = { spans: [], logs: [] };
Deno.serve({ port: 4318 }, async (req) => {
  const body = await req.json();
  body.resourceLogs?.forEach(r => r.scopeLogs.forEach(s => data.logs.push(...s.logRecords)));
  body.resourceSpans?.forEach(r => r.scopeSpans.forEach(s => data.spans.push(...s.spans)));
  Deno.writeTextFileSync(`otel-${new Date().toISOString().split('T')[0]}.json`, JSON.stringify(data));
  return Response.json({ partialSuccess: {} });
});

Then set OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4318 and OTEL_EXPORTER_OTLP_PROTOCOL=http/json.

[acrodrig]

This is very nice, thanks for taking the time to write it

[luckyman0026]

You could try using a simple file exporter in OpenTelemetry. Most OTEL SDKs support exporting traces or metrics to a local file instead of sending them to a full server. For example, in Deno, you could write a small script to collect OTEL data and append it to a file per day. Even a basic implementation that writes JSON lines to a .log file can work. This way, you avoid setting up Grafana but still capture all the data for later analysis.