Add a very basic prometheus exporter #2143
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| configure?.Invoke(options); | ||
| var exporter = new PrometheusExporter(options); | ||
| var pullMetricProcessor = new PullMetricProcessor(exporter, false); | ||
| exporter.MakePullRequest = pullMetricProcessor.PullRequest; |
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some tricks to make the "pull request" from scrape request.
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| using var output = ctx.Response.OutputStream; | ||
| using var writer = new StreamWriter(output); | ||
| this.exporter.MakePullRequest(); |
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calling MakePullRequest() will request the metrics from the in-memory aggregation store, and cause it to call Export() method, which stores the metric inside Exporter..
the next line this.exporter.WriteMetricsCollection simply writes the stored metric inside exporter.
| System.Console.ReadLine(); | ||
| using var meterProvider = Sdk.CreateMeterProviderBuilder() | ||
| .AddSource("TestMeter") | ||
| .AddPrometheusExporter(opt => opt.Url = $"http://localhost:{port}/metrics/") |
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I like the simplicity here. User is not expected to anything about temporality (delta vs cumulative)!. Hope it can stay that way..
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Seems reasonable, because Prometheus is always cumulative right? I guess the only thing that would change this is if Prometheus introduced support for delta aggregations.
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yea.. Views will likely make this more complex :)
src/OpenTelemetry.Exporter.Prometheus/Implementation/PrometheusExporterEventSource.cs
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| { | ||
| public const string ContentType = "text/plain; version = 0.0.4"; | ||
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| private static readonly char[] FirstCharacterNameCharset = |
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Consider something like FirstCharacterNameCharset = "abcde".ToCharArray().
| // Label names may contain ASCII letters, numbers, as well as underscores. They must match the regex [a-zA-Z_][a-zA-Z0-9_]*. Label names beginning with __ are reserved for internal use. | ||
| // Label values may contain any Unicode characters. | ||
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| var sb = new StringBuilder(); |
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- creating a string builder for each call could be very expensive, at minimum we need to cache it.
- instead of doing the conversion each time, it might make sense to cache some frequently used value (e.g. consider some data structure such as splay tree).
| // (\), double-quote ("), and line feed (\n) characters have to be escaped | ||
| // as \\, \", and \n, respectively. | ||
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| var result = value.Replace("\\", "\\\\"); |
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This would scan the string 3 times, with extra allocations. There might be an optimal way.
src/OpenTelemetry.Exporter.Prometheus/PrometheusExporterMetricsHttpServer.cs
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src/OpenTelemetry.Exporter.Prometheus/PrometheusExporterMetricsHttpServer.cs
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Thanks. Prometheus part was just copied from old exporter to do some initial test. Prometheus will be reworked later to address perf (and other issues). |
Codecov Report
@@ Coverage Diff @@
## metrics #2143 +/- ##
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Coverage 78.24% 78.24%
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Files 212 212
Lines 6634 6634
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Hits 5191 5191
Misses 1443 1443 |
| </ItemGroup> | ||
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| <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'"> | ||
| <PackageReference Include="Microsoft.AspNetCore.Http.Abstractions" Version="$(MicrosoftAspNetCoreHttpAbstractionsPkgVer)" /> |
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At some point it might make sense to pull the middleware into a separate extension package specifically for ASP.NET Core apps.
Just basic one, showing Sum metrics from a sync. counter :)
Adding it now itself, as it kinda shows a true "Pull exporter", requiring Cumulative temporality.
The "in-memory aggregation state" is collected only upon a scrape request. (once we add support for async instruments, they'll be collected only upon a scrape request)
Note: Most of Prometheus code was resurrected from ~2year old one. Consider this as a initial version (and be gentle with PR comments on prometheus part :D ), just to keep things moving :)
Sample output from scraping:
