cmd/utils: guard SampleRatio flag with IsSet check#34062
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jwasinger
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Mar 23, 2026
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jrhea
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May 13, 2026
## Summary The `--rpc.telemetry.sample-ratio` flag declares `Value: 1.0` and `geth --help` advertises `(default: 1)`. In practice, however, omitting the flag produces a sample ratio of `0`, causing `sdktrace.TraceIDRatioBased(0)` to drop 100% of spans. Users who enable `--rpc.telemetry` see the `OpenTelemetry trace export enabled` log line and a clean startup, but no traces ever leave the process. The root cause is the interaction between two pieces of code: 1. `cmd/utils/flags.go:setOpenTelemetry` (added in #34062) only copies the flag value when `ctx.IsSet(...)` returns true: ```go if ctx.IsSet(RPCTelemetrySampleRatioFlag.Name) { tcfg.SampleRatio = ctx.Float64(RPCTelemetrySampleRatioFlag.Name) } ``` That is the right pattern for "don't clobber a config-file value with the CLI default," but it implies that something else must initialise the field when neither source sets it. 2. `node/defaults.go:DefaultConfig` never initialises `OpenTelemetry.SampleRatio`, leaving it at the float64 zero value. The result for the common CLI-only user (no TOML config) is `SampleRatio = 0` → every span is silently dropped, despite the documented default of 1. ## Change Seed `OpenTelemetry: OpenTelemetryConfig{SampleRatio: 1.0}` in `node.DefaultConfig` so the documented default matches runtime behavior and the `ctx.IsSet` guard in `setOpenTelemetry` continues to do what it was designed to do.
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In
setOpenTelemetry, all other fields (Enabled, Endpoint, AuthUser, AuthPassword, InstanceID, Tags) are guarded byctx.IsSet()checks, so they only override the config file when explicitly set via CLI flags.SampleRatiowas the only field missing this guard, causing the flag default (1.0) to always overwrite whatever was loaded from the config file.SampleRatiobeing unconditionally overwritten by the CLI flag default value (1.0), even when the user did not pass--rpc.telemetry.sample-ratioSampleRatioto be silently ignored