[hostmetrics] Add warning on startup if running in docker with no oth…

…er root defined. (open-telemetry#17290)

In the event that the container is started in a docker container but
doesn't have a root path, it is likely that it will report the
container's stats which is misleading and hard to diagnose

Co-authored-by: Dmitrii Anoshin <[email protected]>

receiver/hostmetricsreceiver/internal/scraper/filesystemscraper/factory.go

@@ -16,6 +16,7 @@ package filesystemscraper // import "github.com/open-telemetry/opentelemetry-col
 
 import (
  "context"
+ "os"
 
  "go.opentelemetry.io/collector/receiver"
  "go.opentelemetry.io/collector/receiver/scraperhelper"
@@ -54,6 +55,25 @@ func (f *Factory) CreateMetricsScraper(
  config internal.Config,
 ) (scraperhelper.Scraper, error) {
  cfg := config.(*Config)
+
+ if cfg.RootPath == "" {
+ inContainer := os.Getpid() == 1
+ for _, p := range []string{
+ "/.dockerenv", // Mounted by dockerd when starting a container by default
+ "/run/.containerenv", // Mounted by podman as described here: https://github.com/containers/podman/blob/ecbb52cb478309cfd59cc061f082702b69f0f4b7/docs/source/markdown/podman-run.1.md.in#L31
+ } {
+ if _, err := os.Stat(p); err == nil {
+
+ break
+ }
+ }
+ if inContainer {
+ settings.Logger.Warn(
+ "No `root_path` config set when running in docker environment, will report container filesystem stats." +
+ " See https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/receiver/hostmetricsreceiver#collecting-host-metrics-from-inside-a-container-linux-only")
+ }
+ }
+
  s, err := newFileSystemScraper(ctx, settings, cfg)
  if err != nil {
  return nil, err