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ring: treat CAS no-change as success during instance registration #1000

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ring: treat CAS no-change as success during instance registration #1000

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13 changes: 12 additions & 1 deletion ring/basic_lifecycler.go
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@ import (
"fmt"
"net/http"
"sort"
"strings"
"sync"
"time"

Expand Down Expand Up @@ -353,7 +354,17 @@ func (l *BasicLifecycler) registerInstance(ctx context.Context) error {
})

if err != nil {
return err
// If the KV store detected no change (the instance's ring entry already matches
// what we tried to write), the registration is effectively successful. This can
// happen when the stored timestamp is ahead of the current time (e.g., clock
// corruption) — the merge function sees no forward progress and returns
// "no change detected." Treating this as fatal causes a permanent CrashLoopBackOff
// because the same no-change result recurs on every restart (issue grafana/loki#21733).
if strings.Contains(err.Error(), "no change detected") {
level.Warn(l.logger).Log("msg", "CAS detected no change during registration; instance already registered with identical state", "ring", l.ringName, "instance", l.cfg.ID, "err", err)
} else {
return err
}
}

l.currState.Lock()
Expand Down