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Jan 6, 2026
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logging: warn about logger.V().Error #8732

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10 changes: 7 additions & 3 deletions contributors/devel/sig-instrumentation/migration-to-structured-logging.md
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Original file line number Diff line number Diff line change
Expand Up @@ -190,12 +190,16 @@ functions need to be used:
- `klog.ErrorS` -> `logger.Error`
- `klog.InfoS` -> `logger.Info`
- `klog.V().InfoS` -> `logger.V().Info`
- `klog.V().ErrorS(err, ...)` -> `logger.V().Info(..., "err", err)`

In all of these cases, `logger` is a `logr.Logger` instance. `klog.Logger` is
an alias for that type. Determining where that instance comes from is the main
challenge when migrating code to contextual logging.
an alias for that type. In contrast to klog, logr ignores verbosity for `Error`
calls and always emits the log. The semantic equivalent of `klog.V().ErrorS` is
therefore an `Info` call where the error is represented as a key/value pair.

Several new klog functions help with that:
Determining where the `Logger` instance comes from is the main challenge when
migrating code to contextual logging. Several new klog functions help with
that:

- [`klog.FromContext`](https://pkg.go.dev/k8s.io/klog/v2#FromContext)
- [`klog.Background`](https://pkg.go.dev/k8s.io/klog/v2#Background)
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