Simple hardware metrics collection + alerting (#115)

* Add CPU and RAM usage alerting

* Create basic troubleshooting document to point alerts at

* Limit max number of hardware values collected

* Save metric value with the point in time it was taken

metrics/hardware.go

@@ -0,0 +1,35 @@
+package metrics
+
+import (
+	"time"
+
+	"github.com/shirou/gopsutil/cpu"
+	"github.com/shirou/gopsutil/mem"
+)
+
+// Max number of metrics we want to keep.
+const maxCollectionValues = 500
+
+func collectCPUUtilization() {
+	if len(Metrics.CPUUtilizations) > maxCollectionValues {
+		Metrics.CPUUtilizations = Metrics.CPUUtilizations[1:]
+	}
+
+	v, err := cpu.Percent(0, false)
+	if err != nil {
+		panic(err)
+	}
+
+	metricValue := value{time.Now(), int(v[0])}
+	Metrics.CPUUtilizations = append(Metrics.CPUUtilizations, metricValue)
+}
+
+func collectRAMUtilization() {
+	if len(Metrics.RAMUtilizations) > maxCollectionValues {
+		Metrics.RAMUtilizations = Metrics.RAMUtilizations[1:]
+	}
+
+	memoryUsage, _ := mem.VirtualMemory()
+	metricValue := value{time.Now(), int(memoryUsage.UsedPercent)}
+	Metrics.RAMUtilizations = append(Metrics.RAMUtilizations, metricValue)
+}