cmd/prometheus: Issue a warning on 32 bit archs (prometheus#8012)

* cmd/prometheus: Issue a warning on 32 bit archs

Signed-off-by: Julien Pivotto <[email protected]>

cmd/prometheus/main.go

@@ -19,6 +19,7 @@ import (
 	"fmt"
 	"io"
 	"math"
+	"math/bits"
 	"net"
 	"net/http"
 	_ "net/http/pprof" // Comment this line to disable pprof endpoint.
@@ -344,6 +345,10 @@ func main() {
 	klog.SetLogger(log.With(logger, "component", "k8s_client_runtime"))
 
 	level.Info(logger).Log("msg", "Starting Prometheus", "version", version.Info())
+	if bits.UintSize < 64 {
+		level.Warn(logger).Log("msg", "This Prometheus binary has not been compiled for a 64-bit architecture. Due to virtual memory constraints of 32-bit systems, it is highly recommended to switch to a 64-bit binary of Prometheus.", "GOARCH", runtime.GOARCH)
+	}
+
 	level.Info(logger).Log("build_context", version.BuildContext())
 	level.Info(logger).Log("host_details", prom_runtime.Uname())
 	level.Info(logger).Log("fd_limits", prom_runtime.FdLimits())