feat: HealthCheck endpoint for nodes

internal/memorystore/healthcheck.go

@@ -0,0 +1,88 @@
+package memorystore
+
+import (
+	"bufio"
+	"fmt"
+	"time"
+)
+
+// This is a threshold that allows a node to be healthy with certain number of data points missing.
+// Suppose a node does not receive last 5 data points, then healthCheck endpoint will still say a
+// node is healthy. Anything more than 5 missing points in metrics of the node will deem the node unhealthy.
+const MaxMissingDataPoints int64 = 5
+
+// This is a threshold which allows upto certain number of metrics in a node to be unhealthly.
+// Works with MaxMissingDataPoints. Say 5 metrics (including submetrics) do not receive the last
+// MaxMissingDataPoints data points, then the node will be deemed healthy. Any more metrics that does
+// not receive data for MaxMissingDataPoints data points will deem the node unhealthy.
+const MaxUnhealthyMetrics int64 = 5
+
+func (b *buffer) healthCheck() int64 {
+
+	// Check if the buffer is empty
+	if b.data == nil {
+		return 1
+	}
+
+	buffer_end := b.start + b.frequency*int64(len(b.data))
+	t := time.Now().Unix()
+
+	// Check if the buffer is too old
+	if t-buffer_end > MaxMissingDataPoints*b.frequency {
+		return 1
+	}
+
+	return 0
+}
+
+func (l *Level) healthCheck(m *MemoryStore, count int64) (int64, error) {
+	l.lock.RLock()
+	defer l.lock.RUnlock()
+
+	for _, mc := range m.Metrics {
+		if b := l.metrics[mc.Offset]; b != nil {
+			count += b.healthCheck()
+		}
+	}
+
+	for _, lvl := range l.children {
+		c, err := lvl.healthCheck(m, 0)
+		if err != nil {
+			return 0, err
+		}
+		count += c
+	}
+
+	return count, nil
+}
+
+func (m *MemoryStore) HealthCheck(w *bufio.Writer, selector []string) error {
+	lvl := m.root.findLevel(selector)
+	if lvl == nil {
+		return fmt.Errorf("not found: %#v", selector)
+	}
+
+	buf := make([]byte, 0, 25)
+	// buf = append(buf, "{"...)
+
+	var count int64 = 0
+
+	unhealthyMetricsCount, err := lvl.healthCheck(m, count)
+	if err != nil {
+		return err
+	}
+
+	if unhealthyMetricsCount < MaxUnhealthyMetrics {
+		buf = append(buf, "Healthy"...)
+	} else {
+		buf = append(buf, "Unhealthy"...)
+	}
+
+	// buf = append(buf, "}\n"...)
+
+	if _, err = w.Write(buf); err != nil {
+		return err
+	}
+
+	return w.Flush()
+}