--dry-run Promtail.

cmd/promtail/main.go

@@ -27,6 +27,7 @@ func init() {
 
 func main() {
 	printVersion := flag.Bool("version", false, "Print this builds version information")
+	dryRun := flag.Bool("dry-run", false, "Start Promtail but print entries instead of sending them to Loki.")
 
 	// Load config, merging config file and CLI flags
 	var config config.Config
@@ -57,7 +58,7 @@ func main() {
 		stages.Debug = true
 	}
 
-	p, err := promtail.New(config)
+	p, err := promtail.New(config, *dryRun)
 	if err != nil {
 		level.Error(util.Logger).Log("msg", "error creating promtail", "error", err)
 		os.Exit(1)

pkg/promtail/client/logger.go

@@ -0,0 +1,56 @@
+package client
+
+import (
+	"fmt"
+	"os"
+	"sync"
+	"text/tabwriter"
+	"time"
+
+	"github.com/cortexproject/cortex/pkg/util"
+	"github.com/fatih/color"
+	"github.com/prometheus/common/model"
+	"gopkg.in/yaml.v2"
+)
+
+type logger struct {
+	*tabwriter.Writer
+	sync.Mutex
+}
+
+// NewLogger creates a new client logger that logs entries instead of sending them.
+func NewLogger(cfgs ...Config) (Client, error) {
+	// make sure the clients config is valid
+	c, err := NewMulti(util.Logger, cfgs...)
+	if err != nil {
+		return nil, err
+	}
+	c.Stop()
+	fmt.Println(color.YellowString("Clients configured:"))
+	for _, cfg := range cfgs {
+		yaml, err := yaml.Marshal(cfg)
+		if err != nil {
+			return nil, err
+		}
+		fmt.Println("----------------------")
+		fmt.Println(string(yaml))
+	}
+	return &logger{
+		Writer: tabwriter.NewWriter(os.Stdout, 0, 4, 0, '\t', 0),
+	}, nil
+}
+
+func (*logger) Stop() {}
+
+func (l *logger) Handle(labels model.LabelSet, time time.Time, entry string) error {
+	l.Lock()
+	defer l.Unlock()
+	fmt.Fprint(l.Writer, color.BlueString(time.Format("2006-01-02T15:04:05")))
+	fmt.Fprint(l.Writer, "\t")
+	fmt.Fprint(l.Writer, color.YellowString(labels.String()))
+	fmt.Fprint(l.Writer, "\t")
+	fmt.Fprint(l.Writer, entry)
+	fmt.Fprint(l.Writer, "\n")
+	l.Flush()
+	return nil
+}

pkg/promtail/client/logger_test.go

@@ -0,0 +1,21 @@
+package client
+
+import (
+	"net/url"
+	"testing"
+	"time"
+
+	"github.com/cortexproject/cortex/pkg/util/flagext"
+	"github.com/prometheus/common/model"
+	"github.com/stretchr/testify/require"
+)
+
+func TestNewLogger(t *testing.T) {
+	_, err := NewLogger([]Config{}...)
+	require.Error(t, err)
+
+	l, err := NewLogger([]Config{{URL: flagext.URLValue{URL: &url.URL{Host: "string"}}}}...)
+	require.NoError(t, err)
+	err = l.Handle(model.LabelSet{"foo": "bar"}, time.Now(), "entry")
+	require.NoError(t, err)
+}

pkg/promtail/promtail.go

@@ -19,7 +19,7 @@ type Promtail struct {
 }
 
 // New makes a new Promtail.
-func New(cfg config.Config) (*Promtail, error) {
+func New(cfg config.Config, dryRun bool) (*Promtail, error) {
 	positions, err := positions.New(util.Logger, cfg.PositionsConfig)
 	if err != nil {
 		return nil, err
@@ -30,12 +30,20 @@ func New(cfg config.Config) (*Promtail, error) {
 		cfg.ClientConfigs = append(cfg.ClientConfigs, cfg.ClientConfig)
 	}
 
-	client, err := client.NewMulti(util.Logger, cfg.ClientConfigs...)
-	if err != nil {
-		return nil, err
+	var cl client.Client
+	if dryRun {
+		cl, err = client.NewLogger(cfg.ClientConfigs...)
+		if err != nil {
+			return nil, err
+		}
+	} else {
+		cl, err = client.NewMulti(util.Logger, cfg.ClientConfigs...)
+		if err != nil {
+			return nil, err
+		}
 	}
 
-	tms, err := targets.NewTargetManagers(util.Logger, positions, client, cfg.ScrapeConfig, &cfg.TargetConfig)
+	tms, err := targets.NewTargetManagers(util.Logger, positions, cl, cfg.ScrapeConfig, &cfg.TargetConfig)
 	if err != nil {
 		return nil, err
 	}
@@ -46,7 +54,7 @@ func New(cfg config.Config) (*Promtail, error) {
 	}
 
 	return &Promtail{
-		client:         client,
+		client:         cl,
 		positions:      positions,
 		targetManagers: tms,
 		server:         server,

pkg/promtail/promtail_test.go

@@ -7,6 +7,7 @@ import (
 	"math"
 	"math/rand"
 	"net/http"
+	"net/url"
 	"os"
 	"path/filepath"
 	"reflect"
@@ -19,18 +20,22 @@ import (
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
 	"github.com/pkg/errors"
+	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/common/model"
 	sd_config "github.com/prometheus/prometheus/discovery/config"
 	"github.com/prometheus/prometheus/discovery/targetgroup"
 	"github.com/prometheus/prometheus/pkg/labels"
 	"github.com/prometheus/prometheus/pkg/textparse"
 	"github.com/prometheus/prometheus/promql"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 
 	"github.com/grafana/loki/pkg/logentry/stages"
 	"github.com/grafana/loki/pkg/logproto"
 	"github.com/grafana/loki/pkg/promtail/api"
+	"github.com/grafana/loki/pkg/promtail/client"
 	"github.com/grafana/loki/pkg/promtail/config"
+	"github.com/grafana/loki/pkg/promtail/positions"
 	"github.com/grafana/loki/pkg/promtail/scrape"
 	"github.com/grafana/loki/pkg/promtail/targets"
 )
@@ -84,7 +89,7 @@ func TestPromtail(t *testing.T) {
 
 	// Run.
 
-	p, err := New(buildTestConfig(t, positionsFileName, testDir))
+	p, err := New(buildTestConfig(t, positionsFileName, testDir), false)
 	if err != nil {
 		t.Error("error creating promtail", err)
 		return
@@ -628,3 +633,25 @@ func randName() string {
 	}
 	return string(b)
 }
+
+func Test_DryRun(t *testing.T) {
+
+	f, err := ioutil.TempFile("/tmp", "Test_DryRun")
+	require.NoError(t, err)
+	defer os.Remove(f.Name())
+
+	_, err = New(config.Config{}, true)
+	require.Error(t, err)
+
+	prometheus.DefaultRegisterer = prometheus.NewRegistry() // reset registry, otherwise you can't create 2 weavework server.
+
+	p, err := New(config.Config{
+		ClientConfig: client.Config{URL: flagext.URLValue{URL: &url.URL{Host: "string"}}},
+		PositionsConfig: positions.Config{
+			PositionsFile: f.Name(),
+			SyncPeriod:    time.Second,
+		},
+	}, false)
+	require.NoError(t, err)
+	require.IsType(t, client.MultiClient{}, p.client)
+}