Add fake memory metrics

Signed-off-by: Julius Volz <[email protected]>

main.go

@@ -29,6 +29,7 @@ func main() {
 	go runCPUSim(4, 0.3, 0.2)
 	go runDiskSim(160*1e9, 0.5*1e6)
 	go runHolidaySim(5*time.Minute, 0.2)
+	go runMemorySim(8*1024*1024*1024, 1200*1024*1024, 2500*1024*1024, 165*1024*1024, 0.5)
 	prometheus.MustRegister(intermittentMetric{})
 
 	select {}

memory.go

@@ -0,0 +1,49 @@
+package main
+
+import (
+	"math/rand"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+var memoryUsage = prometheus.NewGaugeVec(
+	prometheus.GaugeOpts{
+		Namespace: namespace,
+		Name:      "memory_usage_bytes",
+		Help:      "The memory usage by type.",
+	},
+	[]string{"type"},
+)
+
+func init() {
+	prometheus.MustRegister(memoryUsage)
+}
+
+func runMemorySim(total, usedBase, cachedBase, buffersBase, maxDeviation float64) {
+	var used, cached, buffers = usedBase, cachedBase, buffersBase
+
+	randomStep := func(current, base float64) float64 {
+		current += (rand.Float64() - 0.5) * 60 * 1024 * 1024
+		if current < base-base*maxDeviation {
+			current = base
+		}
+		if current > base+base*maxDeviation {
+			current = base
+		}
+		return current
+	}
+
+	for {
+		used = randomStep(used, usedBase)
+		cached = randomStep(cached, cachedBase)
+		buffers = randomStep(buffers, buffersBase)
+
+		memoryUsage.WithLabelValues("used").Set(used)
+		memoryUsage.WithLabelValues("cached").Set(cached)
+		memoryUsage.WithLabelValues("buffers").Set(buffers)
+		memoryUsage.WithLabelValues("free").Set(total - used - cached - buffers)
+
+		time.Sleep(100 * time.Millisecond)
+	}
+}