Document telemetry in README, backtrace only on crash, ignore errors

README.md

@@ -88,13 +88,30 @@ k0sctl completion > /usr/local/share/zsh/site-functions/_k0sctl
 k0sctl completion > ~/.config/fish/completions/k0sctl.fish
 ```
 
+## Anonymous telemetry
+
+K0sctl will send anonymized telemetry data when used. This can be disabled by using the `--disable-telemetry` flag or setting `DISABLE_TELEMETRY=true` environment variable.
+
+The telemetry data includes:
+
+- K0sctl version
+- Operating system + CPU architecture ("linux x86", "darwin arm64", ...)
+- An anonymous machine ID generated by [denisbrodbeck/machineid](https://github.com/denisbrodbeck/machineid) or if that fails, an md5 sum of the hostname
+- Event information:
+  * Phase name ("Connecting to hosts", "Gathering facts", ...) and the duration how long it took to finish
+  * Possible crash error message without identifying information
+  * Cluster UUID (`kubectl get -n kube-system namespace kube-system -o template={{.metadata.uid}}`)
+  * Was k0s dynamic config enabled (true/false)
+  * Was a custom or the default k0s configuration used (true/false)
+
+The data is used to estimate the number of users and to identify failure hotspots.
+
 ## Development status
 
 K0sctl is ready for use and in continuous development. It is still at a stage where maintaining backwards compatibility is not a high priority goal.
 
 Missing major features include at least:
 
-* Windows targets are not yet supported
 * The released binaries have not been signed
 * Nodes can't be removed
 * The configuration specification and command-line interface options are still evolving

main.go

@@ -1,17 +1,33 @@
 package main
 
 import (
-	"fmt"
 	"os"
+	"regexp"
 
 	"github.com/k0sproject/k0sctl/analytics"
 	"github.com/k0sproject/k0sctl/cmd"
 	log "github.com/sirupsen/logrus"
 )
 
+func cleanError(e any) string {
+	if err, ok := e.(error); ok {
+		ipRE := regexp.MustCompile(`\d+\.\d+\.\d+\.\d+`)
+		hostRE := regexp.MustCompile(`(?:[a-zA-Z0-9]\.){1,}[a-zA-Z0-9]{2,6}`)
+		userRE := regexp.MustCompile(`[a-zA-Z0-9]+@\w+`)
+
+		res := ipRE.ReplaceAllString(err.Error(), "[...]")
+		res = hostRE.ReplaceAllString(res, "[...]")
+		res = userRE.ReplaceAllString(res, "[...]@")
+
+		return res
+	}
+
+	return "unknown"
+}
+
 func handlepanic() {
 	if err := recover(); err != nil {
-		_ = analytics.Client.Publish("panic", map[string]interface{}{"error": fmt.Sprint(err)})
+		_ = analytics.Client.Publish("panic", map[string]interface{}{"error": cleanError(err)})
 		log.Fatalf("PANIC: %s", err)
 	}
 }