Repository: grafana/agent (go)

Issue:
failed to unregister all metrics from previous promtail. THIS IS A BUG
I want to use metrics pipeline_stages count the number of error rows in the log. Below is my configuration
```yaml
apiVersion: monitoring.grafana.com/v1alpha1
kind: PodLogs
metadata:
  labels:
    app.kubernetes.io/instance: loki
    app.kubernetes.io/name: loki
  name: mysql
  namespace: loki
spec:
  namespaceSelector:
    matchNames:
    - default
  selector:
    matchLabels:
      app: mysql
  relabelings:
  - action: replace
    sourceLabels:
    - __meta_kubernetes_pod_node_name
    targetLabel: __host__
  - action: labelmap
    regex: __meta_kubernetes_pod_label_(.+)
  - action: replace
    replacement: mysql
    targetLabel: job
  - action: replace
    sourceLabels:
    - __meta_kubernetes_pod_container_name
    targetLabel: container
  - action: replace
    replacement: mysql
    targetLabel: cluster
  pipelineStages:
  - docker: {}
  - match:
      selector: '{container="mysql"} |~ ".*[ERROR].*"'
      stages: |
        - regex:
            expression: ".*(?P<error>[ERROR]).*"
        - metrics:
            error_log_lines_total:
              type: Counter
              description: The total number of error log lines
              source: error
              action: inc
```
After the loki-logs pod restarts, I get an error
```
$ kubectl -n loki logs -f loki-logs-2snl9 grafana-agent 
ts=2023-01-12T02:03:50.543250808Z caller=server.go:195 level=info msg="server listening on addresses" http=[::]:8080 grpc=127.0.0.1:12346 http_tls_enabled=false grpc_tls_enabled=false
ts=2023-01-12T02:03:50.579742291Z caller=node.go:85 level=info agent=prometheus component=cluster msg="applying config"
ts=2023-01-12T02:03:50.579889027Z caller=remote.go:180 level=info agent=prometheus component=cluster msg="not watching the KV, none set"
ts=2023-01-12T02:03:50.616783411Z caller=kubernetes.go:313 level=info component=logs logs_config=loki/loki component=discovery discovery=kubernetes msg="Using pod service account via in-cluster config"
ts=2023-01-12T02:03:50.973238948Z caller=kubernetes.go:313 level=info component=logs logs_config=loki/loki component=discovery discovery=kubernetes msg="Using pod service account via in-cluster config"
ts=2023-01-12T02:03:50Z level=info caller=traces/traces.go:143 msg="Traces Logger Initialized" component=traces
ts=2023-01-12T02:03:51.151720301Z caller=integrations.go:138 level=warn msg="integrations-next is enabled. integrations-next is subject to change"
ts=2023-01-12T02:03:51.220365818Z caller=reporter.go:107 level=info msg="running usage stats reporter"
ts=2023-01-12T02:03:55.336275999Z caller=entrypoint.go:246 level=info msg="reload of config file requested"
ts=2023-01-12T02:03:55.520499461Z caller=entrypoint.go:161 level=error msg="failed to update loki" err="failed to unregister all metrics from previous promtail. THIS IS A BUG"
ts=2023-01-12T02:03:55.520617191Z caller=entrypoint.go:257 level=error msg="failed to reload config file" err="changes did not apply successfully"
ts=2023-01-12T02:04:00.336698444Z caller=entrypoint.go:246 level=info msg="reload of config file requested"
```
When I delete metrics pipeline_stages, everything is normal. My deployment method is helm
```
helm install --namespace=loki --values values.yaml loki loki-3.8.0.tgz
```
Please help me with this, thanks

Pull request description:
Fix issue with config reload when using a log pipeline with a metric stage
#### PR Description

There is a longstanding bug which prevents the agent config from being reloaded when there is a `metrics` stage in a logging pipeline. 

#### Which issue(s) this PR fixes

Fixes #2754

#### PR Checklist

<!-- Remove items that do not apply. For completed items, change [ ] to [x]. -->

- [x] CHANGELOG.md updated
- [x] Documentation added
- [x] Tests updated
- [ ] Config converters updated

Patch:
diff --git a/CHANGELOG.md b/CHANGELOG.md
index c6dad47fe..eb11eaf5a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,14 @@ Main (unreleased)
 - A new `otelcol.exporter.debug` component for printing OTel telemetry from 
   other `otelcol` components to the console. (@BarunKGP)
 
+### Bugfixes
+
+- Fix an issue which caused the config to be reloaded if a config reload was triggered but the config hasn't changed.
+  The bug only affected the "metrics" and "logs" subsystems in Static mode. (@ptodev)
+
+- Fix a bug in Static mode and Flow which prevented config reloads to work if a Loki `metrics` stage is in the pipeline.
+  This resulted in a "failed to unregister all metrics from previous promtail" message. (@ptodev)
+
 v0.41.1 (2024-06-07)
 --------------------
 
@@ -28,11 +36,6 @@ v0.41.1 (2024-06-07)
 
 - Updated pyroscope to v0.4.6 introducing `symbols_map_size` and `pid_map_size` configuration. (@simonswine)
 
-### Bugfixes
-
-- Fix an issue which caused the config to be reloaded if a config reload was triggered but the config hasn't changed.
-  The bug only affected the "metrics" and "logs" subsystems in Static mode.
-
 v0.41.0 (2024-05-31)
 --------------------
 
diff --git a/docs/sources/flow/reference/components/loki.process.md b/docs/sources/flow/reference/components/loki.process.md
index 05eb467d6..ac8307a0e 100644
--- a/docs/sources/flow/reference/components/loki.process.md
+++ b/docs/sources/flow/reference/components/loki.process.md
@@ -717,6 +717,10 @@ The following blocks are supported inside the definition of `stage.metrics`:
 | metric.gauge     | [metric.gauge][]     | Defines a `gauge` metric.     | no       |
 | metric.histogram | [metric.histogram][] | Defines a `histogram` metric. | no       |
 
+{{< admonition type="note" >}}
+The metrics will be reset if you reload the {{< param "PRODUCT_ROOT_NAME" >}} configuration file.
+{{< /admonition >}}
+
 [metric.counter]: #metriccounter-block
 [metric.gauge]: #metricgauge-block
 [metric.histogram]: #metrichistogram-block
diff --git a/internal/component/loki/process/process.go b/internal/component/loki/process/process.go
index b084582a9..b7d0e8eb1 100644
--- a/internal/component/loki/process/process.go
+++ b/internal/component/loki/process/process.go
@@ -127,7 +127,7 @@ func (c *Component) Update(args component.Arguments) error {
 		if err != nil {
 			return err
 		}
-		c.entryHandler = loki.NewEntryHandler(c.processOut, func() {})
+		c.entryHandler = loki.NewEntryHandler(c.processOut, func() { pipeline.Cleanup() })
 		c.processIn = pipeline.Wrap(c.entryHandler).Chan()
 		c.stages = newArgs.Stages
 	}
diff --git a/internal/util/unregisterer.go b/internal/util/unregisterer.go
index 822132b01..eedcabc24 100644
--- a/internal/util/unregisterer.go
+++ b/internal/util/unregisterer.go
@@ -18,6 +18,38 @@ func WrapWithUnregisterer(reg prometheus.Registerer) *Unregisterer {
 	}
 }
 
+// An "unchecked collector" is a collector which returns an empty description.
+// It is described in the Prometheus documentation, here:
+// https://pkg.go.dev/github.com/prometheus/client_golang/prometheus#hdr-Custom_Collectors_and_constant_Metrics
+//
+// > Alternatively, you could return no Desc at all, which will mark the Collector “unchecked”.
+// > No checks are performed at registration time, but metric consistency will still be ensured at scrape time,
+// > i.e. any inconsistencies will lead to scrape errors. Thus, with unchecked Collectors,
+// > the responsibility to not collect metrics that lead to inconsistencies in the total scrape result
+// > lies with the implementer of the Collector. While this is not a desirable state, it is sometimes necessary.
+// > The typical use case is a situation where the exact metrics to be returned by a Collector cannot be predicted
+// > at registration time, but the implementer has sufficient knowledge of the whole system to guarantee metric consistency.
+//
+// Unchecked collectors are used in the Loki "metrics" stage of the Loki "process" component.
+//
+// The isUncheckedCollector function is similar to how Prometheus' Go client extracts the metric description:
+// https://github.com/prometheus/client_golang/blob/45f1e72421d9d11af6be784ad60b7389f7543e70/prometheus/registry.go#L372-L381
+func isUncheckedCollector(c prometheus.Collector) bool {
+	descChan := make(chan *prometheus.Desc, 10)
+
+	go func() {
+		c.Describe(descChan)
+		close(descChan)
+	}()
+
+	i := 0
+	for range descChan {
+		i += 1
+	}
+
+	return i == 0
+}
+
 // Register implements prometheus.Registerer.
 func (u *Unregisterer) Register(c prometheus.Collector) error {
 	if u.wrap == nil {
@@ -28,6 +60,11 @@ func (u *Unregisterer) Register(c prometheus.Collector) error {
 	if err != nil {
 		return err
 	}
+
+	if isUncheckedCollector(c) {
+		return nil
+	}
+
 	u.cs[c] = struct{}{}
 	return nil
 }
@@ -43,6 +80,10 @@ func (u *Unregisterer) MustRegister(cs ...prometheus.Collector) {
 
 // Unregister implements prometheus.Registerer.
 func (u *Unregisterer) Unregister(c prometheus.Collector) bool {
+	if isUncheckedCollector(c) {
+		return true
+	}
+
 	if u.wrap != nil && u.wrap.Unregister(c) {
 		delete(u.cs, c)
 		return true


Test patch:
diff --git a/internal/component/loki/process/process_test.go b/internal/component/loki/process/process_test.go
index 8a423c02a..5256bbcbc 100644
--- a/internal/component/loki/process/process_test.go
+++ b/internal/component/loki/process/process_test.go
@@ -4,7 +4,9 @@ package process
 
 import (
 	"context"
+	"fmt"
 	"os"
+	"strings"
 	"testing"
 	"time"
 
@@ -18,12 +20,15 @@ import (
 	"github.com/grafana/loki/pkg/logproto"
 	"github.com/grafana/river"
 	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/testutil"
 	"github.com/prometheus/common/model"
 	"github.com/stretchr/testify/require"
 	"go.uber.org/atomic"
 	"go.uber.org/goleak"
 )
 
+const logline = `{"log":"log message\n","stream":"stderr","time":"2019-04-30T02:12:41.8443515Z","extra":"{\"user\":\"smith\"}"}`
+
 func TestJSONLabelsStage(t *testing.T) {
 	defer goleak.VerifyNone(t, goleak.IgnoreTopFunction("go.opencensus.io/stats/view.(*worker).start"))
 
@@ -91,7 +96,6 @@ func TestJSONLabelsStage(t *testing.T) {
 
 	// Send a log entry to the component's receiver.
 	ts := time.Now()
-	logline := `{"log":"log message\n","stream":"stderr","time":"2019-04-30T02:12:41.8443515Z","extra":"{\"user\":\"smith\"}"}`
 	logEntry := loki.Entry{
 		Labels: model.LabelSet{"filename": "/var/log/pods/agent/agent/1.log", "foo": "bar"},
 		Entry: logproto.Entry{
@@ -454,7 +458,6 @@ func TestDeadlockWithFrequentUpdates(t *testing.T) {
 	go func() {
 		for {
 			ts := time.Now()
-			logline := `{"log":"log message\n","stream":"stderr","time":"2019-04-30T02:12:41.8443515Z","extra":"{\"user\":\"smith\"}"}`
 			logEntry := loki.Entry{
 				Labels: model.LabelSet{"filename": "/var/log/pods/agent/agent/1.log", "foo": "bar"},
 				Entry: logproto.Entry{
@@ -486,3 +489,189 @@ func TestDeadlockWithFrequentUpdates(t *testing.T) {
 	time.Sleep(1 * time.Second)
 	require.WithinDuration(t, time.Now(), lastSend.Load().(time.Time), 300*time.Millisecond)
 }
+
+func TestMetricsStageRefresh(t *testing.T) {
+	tester := newTester(t)
+	defer tester.stop()
+
+	forwardArgs := `
+	// This will be filled later
+	forward_to = []`
+
+	numLogsToSend := 3
+
+	cfgWithMetric := `
+	stage.metrics { 
+        metric.counter {
+          name = "paulin_test"
+          action = "inc"
+          match_all = true
+        }
+	}` + forwardArgs
+
+	cfgWithMetric_Metrics := `
+	# HELP loki_process_custom_paulin_test
+	# TYPE loki_process_custom_paulin_test counter
+	loki_process_custom_paulin_test{filename="/var/log/pods/agent/agent/1.log",foo="bar"} %d
+	`
+
+	// The component will be reconfigured so that it has a metric.
+	t.Run("config with a metric", func(t *testing.T) {
+		tester.updateAndTest(numLogsToSend, cfgWithMetric,
+			"",
+			fmt.Sprintf(cfgWithMetric_Metrics, numLogsToSend))
+	})
+
+	// The component will be "updated" with the same config.
+	// We expect the metric to stay the same before logs are sent - the component should be smart enough to
+	// know that the new config is the same as the old one and it should just keep running as it is.
+	// If it resets the metric, this could cause issues with some users who have a sidecar "autoreloader"
+	// which reloads the collector config every X seconds.
+	// Those users wouldn't expect their metrics to be reset every time the config is reloaded.
+	t.Run("config with the same metric", func(t *testing.T) {
+		tester.updateAndTest(numLogsToSend, cfgWithMetric,
+			fmt.Sprintf(cfgWithMetric_Metrics, numLogsToSend),
+			fmt.Sprintf(cfgWithMetric_Metrics, 2*numLogsToSend))
+	})
+
+	// Use a config which has no metrics stage.
+	// This should cause the metric to disappear.
+	cfgWithNoStages := forwardArgs
+	t.Run("config with no metrics stage", func(t *testing.T) {
+		tester.updateAndTest(numLogsToSend, cfgWithNoStages, "", "")
+	})
+
+	// Use a config which has a metric with a different name,
+	// as well as a metric with the same name as the one in the previous config.
+	// We try having a metric with the same name as before so that we can see if there
+	// is some sort of double registration error for that metric.
+	cfgWithTwoMetrics := `
+	stage.metrics { 
+		metric.counter {
+		  name = "paulin_test_3"
+		  action = "inc"
+		  match_all = true
+		}
+        metric.counter {
+          name = "paulin_test"
+          action = "inc"
+          match_all = true
+        }
+	}` + forwardArgs
+
+	expectedMetrics3 := `
+	# HELP loki_process_custom_paulin_test_3
+	# TYPE loki_process_custom_paulin_test_3 counter
+	loki_process_custom_paulin_test_3{filename="/var/log/pods/agent/agent/1.log",foo="bar"} %d
+	# HELP loki_process_custom_paulin_test
+	# TYPE loki_process_custom_paulin_test counter
+	loki_process_custom_paulin_test{filename="/var/log/pods/agent/agent/1.log",foo="bar"} %d
+	`
+
+	t.Run("config with a new and old metric", func(t *testing.T) {
+		tester.updateAndTest(numLogsToSend, cfgWithTwoMetrics,
+			"",
+			fmt.Sprintf(expectedMetrics3, numLogsToSend, numLogsToSend))
+	})
+}
+
+type tester struct {
+	t            *testing.T
+	component    *Component
+	registry     *prometheus.Registry
+	cancelFunc   context.CancelFunc
+	logReceiver  loki.LogsReceiver
+	logTimestamp time.Time
+	logEntry     loki.Entry
+	wantLabelSet model.LabelSet
+}
+
+// Create the component, so that it can process and forward logs.
+func newTester(t *testing.T) *tester {
+	reg := prometheus.NewRegistry()
+
+	opts := component.Options{
+		Logger:        util.TestFlowLogger(t),
+		Registerer:    reg,
+		OnStateChange: func(e component.Exports) {},
+	}
+
+	initialCfg := `forward_to = []`
+	var args Arguments
+	err := river.Unmarshal([]byte(initialCfg), &args)
+	require.NoError(t, err)
+
+	logReceiver := loki.NewLogsReceiver()
+	args.ForwardTo = []loki.LogsReceiver{logReceiver}
+
+	c, err := New(opts, args)
+	require.NoError(t, err)
+
+	ctx, cancel := context.WithCancel(context.Background())
+	go c.Run(ctx)
+
+	logTimestamp := time.Now()
+
+	return &tester{
+		t:            t,
+		component:    c,
+		registry:     reg,
+		cancelFunc:   cancel,
+		logReceiver:  logReceiver,
+		logTimestamp: logTimestamp,
+		logEntry: loki.Entry{
+			Labels: model.LabelSet{"filename": "/var/log/pods/agent/agent/1.log", "foo": "bar"},
+			Entry: logproto.Entry{
+				Timestamp: logTimestamp,
+				Line:      logline,
+			},
+		},
+		wantLabelSet: model.LabelSet{
+			"filename": "/var/log/pods/agent/agent/1.log",
+			"foo":      "bar",
+		},
+	}
+}
+
+func (t *tester) stop() {
+	t.cancelFunc()
+}
+
+func (t *tester) updateAndTest(numLogsToSend int, cfg, expectedMetricsBeforeSendingLogs, expectedMetricsAfterSendingLogs string) {
+	var args Arguments
+	err := river.Unmarshal([]byte(cfg), &args)
+	require.NoError(t.t, err)
+
+	args.ForwardTo = []loki.LogsReceiver{t.logReceiver}
+
+	t.component.Update(args)
+
+	// Check the component metrics.
+	if err := testutil.GatherAndCompare(t.registry,
+		strings.NewReader(expectedMetricsBeforeSendingLogs)); err != nil {
+		require.NoError(t.t, err)
+	}
+
+	// Send logs.
+	for i := 0; i < numLogsToSend; i++ {
+		t.component.receiver.Chan() <- t.logEntry
+	}
+
+	// Receive logs.
+	for i := 0; i < numLogsToSend; i++ {
+		select {
+		case logEntry := <-t.logReceiver.Chan():
+			require.True(t.t, t.logTimestamp.Equal(logEntry.Timestamp))
+			require.Equal(t.t, logline, logEntry.Line)
+			require.Equal(t.t, t.wantLabelSet, logEntry.Labels)
+		case <-time.After(5 * time.Second):
+			require.FailNow(t.t, "failed waiting for log line")
+		}
+	}
+
+	// Check the component metrics.
+	if err := testutil.GatherAndCompare(t.registry,
+		strings.NewReader(expectedMetricsAfterSendingLogs)); err != nil {
+		require.NoError(t.t, err)
+	}
+}
diff --git a/internal/util/unregisterer_test.go b/internal/util/unregisterer_test.go
new file mode 100644
index 000000000..e35cfbe6c
--- /dev/null
+++ b/internal/util/unregisterer_test.go
@@ -0,0 +1,35 @@
+package util
+
+import (
+	"testing"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/stretchr/testify/require"
+)
+
+func Test_UnregisterTwice_NormalCollector(t *testing.T) {
+	u := WrapWithUnregisterer(prometheus.NewRegistry())
+	c := prometheus.NewCounter(prometheus.CounterOpts{
+		Name: "test_metric",
+		Help: "Test metric.",
+	})
+	u.Register(c)
+	require.True(t, u.Unregister(c))
+	require.False(t, u.Unregister(c))
+}
+
+type uncheckedCollector struct{}
+
+func (uncheckedCollector) Describe(chan<- *prometheus.Desc) {}
+
+func (uncheckedCollector) Collect(chan<- prometheus.Metric) {}
+
+var _ prometheus.Collector = uncheckedCollector{}
+
+func Test_UnregisterTwice_UncheckedCollector(t *testing.T) {
+	u := WrapWithUnregisterer(prometheus.NewRegistry())
+	c := uncheckedCollector{}
+	u.Register(c)
+	require.True(t, u.Unregister(c))
+	require.True(t, u.Unregister(c))
+}
diff --git a/static/logs/logs_test.go b/static/logs/logs_test.go
index 9ff1f1465..42472befc 100644
--- a/static/logs/logs_test.go
+++ b/static/logs/logs_test.go
@@ -3,7 +3,6 @@
 package logs
 
 import (
-	"bytes"
 	"fmt"
 	"net"
 	"net/http"
@@ -19,6 +18,7 @@ import (
 	"github.com/grafana/agent/internal/util"
 	"github.com/grafana/loki/pkg/logproto"
 	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/testutil"
 	"github.com/stretchr/testify/require"
 	"gopkg.in/yaml.v2"
 )
@@ -38,6 +38,8 @@ func checkConfigReloadLog(t *testing.T, logs string, expectedOccurances int) {
 }
 
 func TestLogs(t *testing.T) {
+	reg := prometheus.NewRegistry()
+
 	//
 	// Create a temporary file to tail
 	//
@@ -87,16 +89,26 @@ configs:
       labels:
         job: test
         __path__: %s
-	`, positionsDir, lis.Addr().String(), tmpFile.Name()))
+    pipeline_stages:
+    - metrics:
+        log_lines_total:
+          type: Counter
+          description: "total number of log lines"
+          prefix: my_promtail_custom_
+          max_idle_duration: 24h
+          config:
+            match_all: true
+            action: inc
+`, positionsDir, lis.Addr().String(), tmpFile.Name()))
 
 	var cfg Config
 	dec := yaml.NewDecoder(strings.NewReader(cfgText))
 	dec.SetStrict(true)
 	require.NoError(t, dec.Decode(&cfg))
 	require.NoError(t, cfg.ApplyDefaults())
-	logBuffer := bytes.Buffer{}
+	logBuffer := util.SyncBuffer{}
 	logger := log.NewSyncLogger(log.NewLogfmtLogger(&logBuffer))
-	l, err := New(prometheus.NewRegistry(), &cfg, logger, false)
+	l, err := New(reg, &cfg, logger, false)
 	require.NoError(t, err)
 	defer l.Stop()
 
@@ -115,6 +127,12 @@ configs:
 	// We expect the config reload log line to not be printed.
 	checkConfigReloadLog(t, logBuffer.String(), 0)
 
+	require.NoError(t, testutil.GatherAndCompare(reg, strings.NewReader(`
+# HELP my_promtail_custom_log_lines_total total number of log lines
+# TYPE my_promtail_custom_log_lines_total counter
+my_promtail_custom_log_lines_total{filename="`+tmpFile.Name()+`",job="test",logs_config="default"} 1
+`), "my_promtail_custom_log_lines_total"))
+
 	//
 	// Apply the same config and try reloading.
 	// Recreate the config struct to make sure it's clean.
@@ -128,6 +146,13 @@ configs:
 
 	checkConfigReloadLog(t, logBuffer.String(), 1)
 
+	// The metrics should stay the same, as the config didn't change.
+	require.NoError(t, testutil.GatherAndCompare(reg, strings.NewReader(`
+# HELP my_promtail_custom_log_lines_total total number of log lines
+# TYPE my_promtail_custom_log_lines_total counter
+my_promtail_custom_log_lines_total{filename="`+tmpFile.Name()+`",job="test",logs_config="default"} 1
+`), "my_promtail_custom_log_lines_total"))
+
 	//
 	// Apply a new config and write a new line.
 	//
@@ -146,7 +171,17 @@ configs:
       labels:
         job: test-2
         __path__: %s
-	`, positionsDir, lis.Addr().String(), tmpFile.Name()))
+    pipeline_stages:
+    - metrics:
+        log_lines_total2:
+          type: Counter
+          description: "total number of log lines"
+          prefix: my_promtail_custom2_
+          max_idle_duration: 24h
+          config:
+            match_all: true
+            action: inc
+`, positionsDir, lis.Addr().String(), tmpFile.Name()))
 
 	var newCfg Config
 	dec = yaml.NewDecoder(strings.NewReader(cfgText))
@@ -155,6 +190,9 @@ configs:
 	require.NoError(t, newCfg.ApplyDefaults())
 	require.NoError(t, l.ApplyConfig(&newCfg, false))
 
+	require.NoError(t, testutil.GatherAndCompare(reg, strings.NewReader(``),
+		"my_promtail_custom_log_lines_total", "my_promtail_custom2_log_lines_total2"))
+
 	fmt.Fprintf(tmpFile, "Hello again!\n")
 	select {
 	case <-time.After(time.Second * 30):
@@ -167,6 +205,13 @@ configs:
 	// We expect the config reload log line to not be printed again.
 	checkConfigReloadLog(t, logBuffer.String(), 1)
 
+	// The metrics changed, and the old metric is no longer visible.
+	require.NoError(t, testutil.GatherAndCompare(reg, strings.NewReader(`
+	# HELP my_promtail_custom2_log_lines_total2 total number of log lines
+	# TYPE my_promtail_custom2_log_lines_total2 counter
+	my_promtail_custom2_log_lines_total2{filename="`+tmpFile.Name()+`",job="test-2",logs_config="default"} 1
+	`), "my_promtail_custom_log_lines_total", "my_promtail_custom2_log_lines_total2"))
+
 	t.Run("update to nil", func(t *testing.T) {
 		// Applying a nil config should remove all instances.
 		err := l.ApplyConfig(nil, false)
diff --git a/static/traces/traces_test.go b/static/traces/traces_test.go
index 2727a5f32..0c9f53820 100644
--- a/static/traces/traces_test.go
+++ b/static/traces/traces_test.go
@@ -225,7 +225,7 @@ configs:
 	err := dec.Decode(&cfg)
 	require.NoError(t, err)
 
-	logBuffer := bytes.Buffer{}
+	logBuffer := util.SyncBuffer{}
 	logger := log.NewLogfmtLogger(&logBuffer)
 
 	traces, err := New(nil, nil, prometheus.NewRegistry(), cfg, logger)