telemetry: Add memory and goroutine metrics, rename container

And fix a typo in a comment, sigh

caddy/caddymain/run.go

@@ -172,7 +172,7 @@ func Run() {
 		AESNI:      cpuid.CPU.AesNi(),
 	})
 	if containerized := detectContainer(); containerized {
-		telemetry.Set("in_container", containerized)
+		telemetry.Set("container", containerized)
 	}
 	telemetry.StartEmitting()
 
@@ -299,7 +299,7 @@ func setCPU(cpu string) error {
 	return nil
 }
 
-// detectContainer attemps to determine whether the process is
+// detectContainer attempts to determine whether the process is
 // being run inside a container. References:
 // https://tuhrig.de/how-to-know-you-are-inside-a-docker-container/
 // https://stackoverflow.com/a/20012536/1048862
@@ -397,7 +397,7 @@ func initTelemetry() error {
 	// initialize telemetry
 	telemetry.Init(id, disabledMetricsSlice)
 
-	// if any metrics were disabled, report it
+	// if any metrics were disabled, report which ones (so we know how representative the data is)
 	if len(disabledMetricsSlice) > 0 {
 		telemetry.Set("disabled_metrics", disabledMetricsSlice)
 		log.Printf("[NOTICE] The following telemetry metrics are disabled: %s", disabledMetrics)

telemetry/telemetry.go

@@ -40,6 +40,7 @@ import (
 	"log"
 	"math/rand"
 	"net/http"
+	"runtime"
 	"strconv"
 	"strings"
 	"sync"
@@ -66,6 +67,9 @@ func emit(final bool) error {
 		return fmt.Errorf("telemetry not enabled")
 	}
 
+	// some metrics are updated/set at time of emission
+	setEmitTimeMetrics()
+
 	// ensure only one update happens at a time;
 	// skip update if previous one still in progress
 	updateMu.Lock()
@@ -228,6 +232,17 @@ func stopUpdateTimer() {
 	updateTimerMu.Unlock()
 }
 
+// setEmitTimeMetrics sets some metrics that should
+// be recorded just before emitting.
+func setEmitTimeMetrics() {
+	Set("goroutines", runtime.NumGoroutine())
+
+	var mem runtime.MemStats
+	runtime.ReadMemStats(&mem)
+	SetNested("memory", "heap_alloc", mem.HeapAlloc)
+	SetNested("memory", "sys", mem.Sys)
+}
+
 // makePayloadAndResetBuffer prepares a payload
 // by emptying the collection buffer. It returns
 // the bytes of the payload to send to the server.