OpenTelemetry

LeanCorpus exposes activities and metrics through the standard BCL APIs. Your app can export them to any OpenTelemetry backend, including Aspire, Jaeger and Prometheus.

Source names

Kind	Name
`ActivitySource`	`Rowles.LeanCorpus`
`Meter`	`Rowles.LeanCorpus`

Activities

Activity	Tags
`leancorpus.search`	`query.type`, `search.total_hits`, `search.cache_hit`
`leancorpus.index.commit`	`index.commit_generation`, `index.segment_count`
`leancorpus.index.flush`	`index.segment_id`, `index.doc_count`
`leancorpus.index.merge`	`index.segments_merged`

Activities are only allocated when a listener is attached.

Metric instruments

leancorpus.search.duration, leancorpus.search.count, leancorpus.cache.hits, leancorpus.cache.misses, leancorpus.index.flush.duration, leancorpus.index.merge.duration, leancorpus.index.merge.segments, leancorpus.index.commit.duration, leancorpus.hnsw.search.duration, leancorpus.hnsw.search.nodes_visited, leancorpus.hnsw.build.duration, leancorpus.hnsw.build.nodes.

Wire MeterMetricsCollector

using Rowles.LeanCorpus.Diagnostics;

var collector = new MeterMetricsCollector();

var writerConfig   = new IndexWriterConfig    { Metrics = collector };
var searcherConfig = new IndexSearcherConfig  { Metrics = collector };

In hosted apps, pass the DI-managed IMeterFactory into MeterMetricsCollector.

OTLP export

Let environment variables configure the endpoint. This keeps the same code working under Aspire AppHost, Aspire Runner and other OTLP collectors.

builder.Services
    .AddOpenTelemetry()
    .ConfigureResource(r => r.AddService("MySearchApp"))
    .WithTracing(t => t
        .AddSource("Rowles.LeanCorpus")
        .AddOtlpExporter())
    .WithMetrics(m => m
        .AddMeter("Rowles.LeanCorpus")
        .AddOtlpExporter());

For a local collector:

$env:OTEL_EXPORTER_OTLP_ENDPOINT = "http://localhost:4317"
$env:OTEL_EXPORTER_OTLP_PROTOCOL = "grpc"

Structured logs

LeanCorpus does not log directly. Application logs can still be exported to the same OTLP endpoint:

builder.Logging.AddOpenTelemetry(logging =>
{
    logging.IncludeFormattedMessage = true;
    logging.IncludeScopes           = true;
    logging.ParseStateValues        = true;
    logging.AddOtlpExporter();
});

Use message templates, not string interpolation, so log values become structured attributes:

logger.LogInformation("Search {QueryType} returned {HitCount} hits", queryType, hits);

Aspire Runner

Aspire Runner defaults to HTTPS for the dashboard and OTLP. If your app uses http://localhost:4317, start the dashboard without HTTPS:

aspire-dashboard -s false

Or set OTEL_EXPORTER_OTLP_ENDPOINT to https://localhost:4317 and trust the certificate used by the dashboard.

A worked example lives in src/examples/Rowles.LeanCorpus.Example.Telemetry.

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