fix(pyroscope.receive_http): Handle metrics registry gracefully (#2302)

This component did not handle duplciate registrations well.

This fixes #2285.

internal/component/pyroscope/receive_http/receive_http.go

@@ -10,6 +10,7 @@ import (
 	"sync"
 
 	"github.com/gorilla/mux"
+	"github.com/prometheus/client_golang/prometheus"
 	"golang.org/x/sync/errgroup"
 
 	"github.com/grafana/alloy/internal/component"
@@ -18,6 +19,7 @@ import (
 	"github.com/grafana/alloy/internal/component/pyroscope/write"
 	"github.com/grafana/alloy/internal/featuregate"
 	"github.com/grafana/alloy/internal/runtime/logging/level"
+	"github.com/grafana/alloy/internal/util"
 )
 
 const (
@@ -53,16 +55,21 @@ func (a *Arguments) SetToDefault() {
 }
 
 type Component struct {
-	opts        component.Options
-	server      *fnet.TargetServer
-	appendables []pyroscope.Appendable
-	mut         sync.Mutex
+	opts               component.Options
+	server             *fnet.TargetServer
+	uncheckedCollector *util.UncheckedCollector
+	appendables        []pyroscope.Appendable
+	mut                sync.Mutex
 }
 
 func New(opts component.Options, args Arguments) (*Component, error) {
+	uncheckedCollector := util.NewUncheckedCollector(nil)
+	opts.Registerer.MustRegister(uncheckedCollector)
+
 	c := &Component{
-		opts:        opts,
-		appendables: args.ForwardTo,
+		opts:               opts,
+		uncheckedCollector: uncheckedCollector,
+		appendables:        args.ForwardTo,
 	}
 
 	if err := c.Update(args); err != nil {
@@ -116,7 +123,14 @@ func (c *Component) Update(args component.Arguments) error {
 
 	c.shutdownServer()
 
-	srv, err := fnet.NewTargetServer(c.opts.Logger, "pyroscope_receive_http", c.opts.Registerer, newArgs.Server)
+	// [server.Server] registers new metrics every time it is created. To
+	// avoid issues with re-registering metrics with the same name, we create a
+	// new registry for the server every time we create one, and pass it to an
+	// unchecked collector to bypass uniqueness checking.
+	serverRegistry := prometheus.NewRegistry()
+	c.uncheckedCollector.SetCollector(serverRegistry)
+
+	srv, err := fnet.NewTargetServer(c.opts.Logger, "pyroscope_receive_http", serverRegistry, newArgs.Server)
 	if err != nil {
 		return fmt.Errorf("failed to create server: %w", err)
 	}

internal/component/pyroscope/receive_http/receive_http_test.go

@@ -287,3 +287,45 @@ func testOptions(t *testing.T) component.Options {
 		Registerer: prometheus.NewRegistry(),
 	}
 }
+
+// TestUpdateArgs verifies that the component can be updated with new arguments. This explictly also makes sure that the server is restarted when the server configuration changes. And there are no metric registration conflicts.
+func TestUpdateArgs(t *testing.T) {
+	ports, err := freeport.GetFreePorts(2)
+	require.NoError(t, err)
+
+	forwardTo := []pyroscope.Appendable{testAppendable(nil)}
+
+	args := Arguments{
+		Server: &fnet.ServerConfig{
+			HTTP: &fnet.HTTPConfig{
+				ListenAddress: "localhost",
+				ListenPort:    ports[0],
+			},
+		},
+		ForwardTo: forwardTo,
+	}
+
+	comp, err := New(testOptions(t), args)
+	require.NoError(t, err)
+
+	ctx, cancel := context.WithCancel(context.Background())
+	t.Cleanup(cancel)
+
+	go func() {
+		require.NoError(t, comp.Run(ctx))
+	}()
+
+	waitForServerReady(t, ports[0])
+
+	comp.Update(Arguments{
+		Server: &fnet.ServerConfig{
+			HTTP: &fnet.HTTPConfig{
+				ListenAddress: "localhost",
+				ListenPort:    ports[1],
+			},
+		},
+		ForwardTo: forwardTo,
+	})
+
+	waitForServerReady(t, ports[1])
+}