Method filterOutReadOnlyInstances

ring/ring.go:1141–1166

filterOutReadOnlyInstances removes all read-only instances from the ring, and returns the resulting ring.

(lookbackPeriod time.Duration, now time.Time)

// filterOutReadOnlyInstances removes all read-only instances from the ring, and returns the resulting ring.
func (r *Ring) filterOutReadOnlyInstances(lookbackPeriod time.Duration, now time.Time) *Ring {
	lookbackUntil := now.Add(-lookbackPeriod).Unix()

	r.mtx.RLock()
	defer r.mtx.RUnlock()

	// If there are no read-only instances, there's no need to do any filtering.
	if r.readOnlyInstances != nil && *r.readOnlyInstances == 0 {
		return r
	}

	// If all readOnlyUpdatedTimestamp values are within lookback window, we can return the ring without any filtering.
	if lookbackPeriod > 0 && r.oldestReadOnlyUpdatedTimestamp != nil && *r.oldestReadOnlyUpdatedTimestamp >= lookbackUntil {
		return r
	}

	shard := make(map[string]InstanceDesc, len(r.ringDesc.Ingesters))

	for id, inst := range r.ringDesc.Ingesters {
		if shouldIncludeReadonlyInstanceInTheShard(inst, lookbackPeriod, lookbackUntil) {
			shard[id] = inst
		}
	}

	return r.buildRingForTheShard(shard)
}

// buildRingForTheShard builds read-only ring for the shard (this ring won't be updated in the future).
func (r *Ring) buildRingForTheShard(shard map[string]InstanceDesc) *Ring {