Support stdin target via flag instead of automatic detection.

This seems to causes issue on some environment so let's use a flag instead.

Fixes grafana#1921

Signed-off-by: Cyril Tovena <cyril.tovena@gmail.com>

docs/clients/promtail/troubleshooting.md

@@ -13,22 +13,22 @@ In dry run mode, Promtail still support reading from a [positions](configuration
 To start Promtail in dry run mode use the flag `--dry-run` as shown in the example below:
 
 ```bash
-cat my.log | promtail --dry-run --client.url http://127.0.0.1:3100/loki/api/v1/push
+cat my.log | promtail --stdin --dry-run --client.url http://127.0.0.1:3100/loki/api/v1/push
 ```
 
 ## Pipe data to Promtail
 
-Promtail supports piping data for sending logs to Loki. This is a very useful way to troubleshooting your configuration.
+Promtail supports piping data for sending logs to Loki (via the flag `--stdin`). This is a very useful way to troubleshooting your configuration.
 Once you have promtail installed you can for instance use the following command to send logs to a local Loki instance:
 
 ```bash
-cat my.log | promtail --client.url http://127.0.0.1:3100/loki/api/v1/push
+cat my.log | promtail --stdin  --client.url http://127.0.0.1:3100/loki/api/v1/push
 ```
 
 You can also add additional labels from command line using:
 
 ```bash
-cat my.log | promtail --client.url http://127.0.0.1:3100/loki/api/v1/push --client.external-labels=k1=v1,k2=v2
+cat my.log | promtail --stdin  --client.url http://127.0.0.1:3100/loki/api/v1/push --client.external-labels=k1=v1,k2=v2
 ```
 
 This will add labels `k1` and `k2` with respective values `v1` and `v2`.
@@ -122,7 +122,7 @@ The following table shows an example of the total delay applied by the backoff a
 with `minbackoff: 100ms` and `maxbackoff: 10s`:
 
 | Retry | Min delay | Max delay | Total min delay | Total max delay |
-| ----- | --------- | --------- | --------------- | --------------- |
+|-------|-----------|-----------|-----------------|-----------------|
 | 1     | 100ms     | 200ms     | 100ms           | 200ms           |
 | 2     | 200ms     | 400ms     | 300ms           | 600ms           |
 | 3     | 400ms     | 800ms     | 700ms           | 1.4s            |

pkg/promtail/targets/filetarget.go

@@ -56,11 +56,13 @@ const (
 // Config describes behavior for Target
 type Config struct {
 	SyncPeriod time.Duration `yaml:"sync_period"`
+	Stdin      bool          `yaml:"stdin"`
 }
 
 // RegisterFlags register flags.
 func (cfg *Config) RegisterFlags(flags *flag.FlagSet) {
 	flags.DurationVar(&cfg.SyncPeriod, "target.sync-period", 10*time.Second, "Period to resync directories being watched and files being tailed.")
+	flags.BoolVar(&cfg.Stdin, "stdin", false, "Set to true to pipe logs to promtail.")
 }
 
 // FileTarget describes a particular set of logs.

pkg/promtail/targets/manager.go

@@ -38,8 +38,8 @@ func NewTargetManagers(
 	var journalScrapeConfigs []scrape.Config
 	var syslogScrapeConfigs []scrape.Config
 
-	if isStdinPipe() {
-		level.Debug(util.Logger).Log("msg", "detected pipe from stdin")
+	if targetConfig.Stdin {
+		level.Debug(util.Logger).Log("msg", "configured to read from stdin")
 		stdin, err := newStdinTargetManager(app, client, scrapeConfigs)
 		if err != nil {
 			return nil, err

pkg/promtail/targets/stdin_target_manager.go

@@ -47,15 +47,6 @@ var (
 	}
 )
 
-func isStdinPipe() bool {
-	info, err := stdIn.Stat()
-	if err != nil {
-		level.Warn(util.Logger).Log("err", err)
-		return false
-	}
-	return info.Mode()&os.ModeCharDevice == 0
-}
-
 type Shutdownable interface {
 	Shutdown()
 }

pkg/promtail/targets/stdin_target_manager_test.go

@@ -148,24 +148,6 @@ func Test_StdinConfigs(t *testing.T) {
 	require.Equal(t, defaultStdInCfg, getStdinConfig([]scrape.Config{}))
 }
 
-type mockFileInfo struct{}
-
-func (mockFileInfo) Name() string       { return "" }
-func (mockFileInfo) Size() int64        { return 1 }
-func (mockFileInfo) Mode() os.FileMode  { return 1 }
-func (mockFileInfo) ModTime() time.Time { return time.Now() }
-func (mockFileInfo) Sys() interface{}   { return nil }
-func (mockFileInfo) IsDir() bool        { return false }
-
-func Test_isPipe(t *testing.T) {
-	fake := newFakeStin("line")
-	fake.FileInfo = &mockFileInfo{}
-	stdIn = fake
-	require.Equal(t, true, isStdinPipe())
-	stdIn = os.Stdin
-	require.Equal(t, false, isStdinPipe())
-}
-
 var stagesConfig = `
 pipeline_stages:
 - template: