autoexport: Add OTEL_METRICS_PRODUCERS environment variable support

CHANGELOG.md

@@ -17,6 +17,9 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 ### Added
 
 - `NewSDK` in `go.opentelemetry.io/contrib/config` now returns a configured SDK with a valid `MeterProvider`. (#4804)
+- Add an EXPERIMENTAL `OTEL_METRICS_PRODUCERS` environment variable to `go.opentelemetry.io/contrib/autoexport` to be set metrics producers. (#5281)
+  -  `prometheus` and `none` are supported values. You can specify multiple producers separated by a comma.
+  - `WithFallbackMetricProducer(func(context.Context) (metric.Producer, error))` allows adding a fallback option if the env var is not set.
 
 ### Changed
 

exporters/autoexport/go.mod

@@ -5,6 +5,8 @@ go 1.21
 require (
 	github.com/prometheus/client_golang v1.19.0
 	github.com/stretchr/testify v1.9.0
+	go.opentelemetry.io/collector/pdata v1.5.0
+	go.opentelemetry.io/contrib/bridges/prometheus v0.50.0
 	go.opentelemetry.io/otel v1.26.0
 	go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc v1.26.0
 	go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp v1.26.0
@@ -26,14 +28,19 @@ require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/go-logr/logr v1.4.1 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
+	github.com/gogo/protobuf v1.3.2 // indirect
 	github.com/grpc-ecosystem/grpc-gateway/v2 v2.19.1 // indirect
+	github.com/json-iterator/go v1.1.12 // indirect
+	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
+	github.com/modern-go/reflect2 v1.0.2 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/prometheus/client_model v0.6.1 // indirect
 	github.com/prometheus/common v0.48.0 // indirect
 	github.com/prometheus/procfs v0.12.0 // indirect
 	go.opentelemetry.io/otel/metric v1.26.0 // indirect
 	go.opentelemetry.io/otel/trace v1.26.0 // indirect
 	go.opentelemetry.io/proto/otlp v1.2.0 // indirect
+	go.uber.org/multierr v1.11.0 // indirect
 	golang.org/x/net v0.24.0 // indirect
 	golang.org/x/sys v0.19.0 // indirect
 	golang.org/x/text v0.14.0 // indirect

exporters/autoexport/go.sum

@@ -4,21 +4,34 @@ github.com/cenkalti/backoff/v4 v4.3.0 h1:MyRJ/UdXutAwSAT+s3wNd7MfTIcy71VQueUuFK3
 github.com/cenkalti/backoff/v4 v4.3.0/go.mod h1:Y3VNntkOUPxTVeUxJ/G5vcM//AlwfmyYozVcomhLiZE=
 github.com/cespare/xxhash/v2 v2.2.0 h1:DC2CZ1Ep5Y4k3ZQ899DldepgrayRUGE6BBZ/cd9Cj44=
 github.com/cespare/xxhash/v2 v2.2.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/go-logr/logr v1.2.2/go.mod h1:jdQByPbusPIv2/zmleS9BjJVeZ6kBagPoEUsqbVz/1A=
 github.com/go-logr/logr v1.4.1 h1:pKouT5E8xu9zeFC39JXRDukb6JFQPXM5p5I91188VAQ=
 github.com/go-logr/logr v1.4.1/go.mod h1:9T104GzyrTigFIr8wt5mBrctHMim0Nb2HLGrmQ40KvY=
 github.com/go-logr/stdr v1.2.2 h1:hSWxHoqTgW2S2qGc0LTAI563KZ5YKYRhT3MFKZMbjag=
 github.com/go-logr/stdr v1.2.2/go.mod h1:mMo/vtBO5dYbehREoey6XUKy/eSumjCCveDpRre4VKE=
+github.com/gogo/protobuf v1.3.2 h1:Ov1cvc58UF3b5XjBnZv7+opcTcQFZebYjWzi34vdm4Q=
+github.com/gogo/protobuf v1.3.2/go.mod h1:P1XiOD3dCwIKUDQYPy72D8LYyHL2YPYrpS2s69NZV8Q=
 github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
 github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
+github.com/google/gofuzz v1.0.0/go.mod h1:dBl0BpW6vV/+mYPU4Po3pmUjxk6FQPldtuIdl/M65Eg=
 github.com/grpc-ecosystem/grpc-gateway/v2 v2.19.1 h1:/c3QmbOGMGTOumP2iT/rCwB7b0QDGLKzqOmktBjT+Is=
 github.com/grpc-ecosystem/grpc-gateway/v2 v2.19.1/go.mod h1:5SN9VR2LTsRFsrEC6FHgRbTWrTHu6tqPeKxEQv15giM=
+github.com/json-iterator/go v1.1.12 h1:PV8peI4a0ysnczrg+LtxykD8LfKY9ML6u2jnxaEnrnM=
+github.com/json-iterator/go v1.1.12/go.mod h1:e30LSqwooZae/UwlEbR2852Gd8hjQvJoHmT4TnhNGBo=
+github.com/kisielk/errcheck v1.5.0/go.mod h1:pFxgyoBC7bSaBwPgfKdkLd5X25qrDl4LWUI2bnpBCr8=
+github.com/kisielk/gotool v1.0.0/go.mod h1:XhKaO+MFFWcvkIS/tQcRk01m1F5IRFswLeQ+oQHNcck=
 github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
 github.com/kr/pretty v0.3.1/go.mod h1:hoEshYVHaxMs3cyo3Yncou5ZscifuDolrwPKZanG3xk=
 github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
 github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
+github.com/modern-go/concurrent v0.0.0-20180228061459-e0a39a4cb421/go.mod h1:6dJC0mAP4ikYIbvyc7fijjWJddQyLn8Ig3JB5CqoB9Q=
+github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd h1:TRLaZ9cD/w8PVh93nsPXa1VrQ6jlwL5oN8l14QlcNfg=
+github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd/go.mod h1:6dJC0mAP4ikYIbvyc7fijjWJddQyLn8Ig3JB5CqoB9Q=
+github.com/modern-go/reflect2 v1.0.2 h1:xBagoLtFs94CBntxluKeaWgTMpvLxC4ur3nMaC9Gz0M=
+github.com/modern-go/reflect2 v1.0.2/go.mod h1:yWuevngMOJpCy52FWWMvUC8ws7m/LJsjYzDa0/r8luk=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/prometheus/client_golang v1.19.0 h1:ygXvpU1AoN1MhdzckN+PyD9QJOSD4x7kmXYlnfbA6JU=
@@ -31,8 +44,16 @@ github.com/prometheus/procfs v0.12.0 h1:jluTpSng7V9hY0O2R9DzzJHYb2xULk9VTR1V1R/k
 github.com/prometheus/procfs v0.12.0/go.mod h1:pcuDEFsWDnvcgNzo4EEweacyhjeA9Zk3cnaOZAZEfOo=
 github.com/rogpeppe/go-internal v1.11.0 h1:cWPaGQEPrBb5/AsnsZesgZZ9yb1OQ+GOISoDNXVBh4M=
 github.com/rogpeppe/go-internal v1.11.0/go.mod h1:ddIwULY96R17DhadqLgMfk9H9tvdUzkipdSkR5nkCZA=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
 github.com/stretchr/testify v1.9.0 h1:HtqpIVDClZ4nwg75+f6Lvsy/wHu+3BoSGCbBAcpTsTg=
 github.com/stretchr/testify v1.9.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
+github.com/yuin/goldmark v1.1.27/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
+github.com/yuin/goldmark v1.2.1/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
+go.opentelemetry.io/collector/pdata v1.5.0 h1:1fKTmUpr0xCOhP/B0VEvtz7bYPQ45luQ8XFyA07j8LE=
+go.opentelemetry.io/collector/pdata v1.5.0/go.mod h1:TYj8aKRWZyT/KuKQXKyqSEvK/GV+slFaDMEI+Ke64Yw=
+go.opentelemetry.io/contrib/bridges/prometheus v0.50.0 h1:akXN45Sg2oS2NOb2xBL0LKeq/oSyEIvc8CC/7XLaB+4=
+go.opentelemetry.io/contrib/bridges/prometheus v0.50.0/go.mod h1:uoFuIBjQ9kWtUv4KbRNq0ExS9BQoWxHrr63JWX/EMb8=
 go.opentelemetry.io/otel v1.26.0 h1:LQwgL5s/1W7YiiRwxf03QGnWLb2HW4pLiAhaA5cZXBs=
 go.opentelemetry.io/otel v1.26.0/go.mod h1:UmLkJHUAidDval2EICqBMbnAd0/m2vmpf/dAM+fvFs4=
 go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc v1.26.0 h1:+hm+I+KigBy3M24/h1p/NHkUx/evbLH0PNcjpMyCHc4=
@@ -63,12 +84,39 @@ go.opentelemetry.io/proto/otlp v1.2.0 h1:pVeZGk7nXDC9O2hncA6nHldxEjm6LByfA2aN8IO
 go.opentelemetry.io/proto/otlp v1.2.0/go.mod h1:gGpR8txAl5M03pDhMC79G6SdqNV26naRm/KDsgaHD8A=
 go.uber.org/goleak v1.3.0 h1:2K3zAYmnTNqV73imy9J1T3WC+gmCePx2hEGkimedGto=
 go.uber.org/goleak v1.3.0/go.mod h1:CoHD4mav9JJNrW/WLlf7HGZPjdw8EucARQHekz1X6bE=
+go.uber.org/multierr v1.11.0 h1:blXXJkSxSSfBVBlC76pxqeO+LN3aDfLQo+309xJstO0=
+go.uber.org/multierr v1.11.0/go.mod h1:20+QtiLqy0Nd6FdQB9TLXag12DsQkrbs3htMFfDN80Y=
+golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
+golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
+golang.org/x/mod v0.2.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
+golang.org/x/mod v0.3.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
+golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
+golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
+golang.org/x/net v0.0.0-20200226121028-0de0cce0169b/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
+golang.org/x/net v0.0.0-20201021035429-f5854403a974/go.mod h1:sp8m0HH+o8qH0wwXwYZr8TS3Oi6o0r6Gce1SSxlDquU=
 golang.org/x/net v0.24.0 h1:1PcaxkF854Fu3+lvBIx5SYn9wRlBzzcnHZSiaFFAb0w=
 golang.org/x/net v0.24.0/go.mod h1:2Q7sJY5mzlzWjKtYUEXSlBWCdyaioyXzRB2RtU8KVE8=
+golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.0.0-20201020160332-67f06af15bc9/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20200930185726-fdedc70b468f/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.19.0 h1:q5f1RH2jigJ1MoAWp2KTp3gm5zAGFUTarQZ5U386+4o=
 golang.org/x/sys v0.19.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
 golang.org/x/text v0.14.0 h1:ScX5w1eTa3QqT8oi6+ziP7dTV1S2+ALU0bI+0zXKWiQ=
 golang.org/x/text v0.14.0/go.mod h1:18ZOQIKpY8NJVqYksKHtTdi31H5itFRjB5/qKTNYzSU=
+golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
+golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
+golang.org/x/tools v0.0.0-20200619180055-7c47624df98f/go.mod h1:EkVYQZoAsY45+roYkvgYkIh4xh/qjgUK9TdY2XT94GE=
+golang.org/x/tools v0.0.0-20210106214847-113979e3529a/go.mod h1:emZCQorbCU4vsT4fOWvOPXz4eW1wZW4PmDk9uLelYpA=
+golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 google.golang.org/genproto v0.0.0-20240227224415-6ceb2ff114de h1:F6qOa9AZTYJXOUEr4jDysRDLrm4PHePlge4v4TGAlxY=
 google.golang.org/genproto v0.0.0-20240227224415-6ceb2ff114de/go.mod h1:VUhTRKeHn9wwcdrk73nvdC9gF178Tzhmt/qyaFcPLSo=
 google.golang.org/genproto/googleapis/api v0.0.0-20240227224415-6ceb2ff114de h1:jFNzHPIeuzhdRwVhbZdiym9q0ory/xY3sA+v2wPg8I0=

exporters/autoexport/metrics.go

@@ -10,11 +10,13 @@
 	"net"
 	"net/http"
 	"os"
+	"strings"
 	"time"
 
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 
+	prometheusbridge "go.opentelemetry.io/contrib/bridges/prometheus"
 	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc"
 	"go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp"
@@ -60,6 +62,9 @@
 // when OTEL_METRICS_EXPORTER is unset or empty.
 //
 // Use [IsNoneMetricReader] to check if the retured exporter is a "no operation" exporter.
+//
+// OTEL_METRICS_PRODUCERS can be used to configure metric producers; supported values: prometheus, none.
+// Use [RegisterMetricProducer] to handle more values of OTEL_METRICS_PRODUCERS.
 func NewMetricReader(ctx context.Context, opts ...MetricOption) (metric.Reader, error) {
 	return metricsSignal.create(ctx, opts...)
 }
@@ -71,10 +76,35 @@
 	must(metricsSignal.registry.store(name, factory))
 }
 
-var metricsSignal = newSignal[metric.Reader]("OTEL_METRICS_EXPORTER")
+// RegisterMetricProducer sets the MetricReader factory to be used when the
+// OTEL_METRICS_PRODUCERS environment variable contains the producer name. This
+// will panic if name has already been registered.
+func RegisterMetricProducer(name string, factory func(context.Context) (metric.Producer, error)) {
+	must(metricsProducers.registry.store(name, factory))
+}
+
+// WithFallbackMetricProducer sets the fallback producer to use when no producer
+// is configured through the OTEL_METRICS_PRODUCERS environment variable.
+func WithFallbackMetricProducer(producerFactory func(ctx context.Context) (metric.Producer, error)) {
+	metricsProducers.fallbackProducer = producerFactory
+}
+
+var (
+	metricsSignal    = newSignal[metric.Reader]("OTEL_METRICS_EXPORTER")
+	metricsProducers = newProducerRegistry("OTEL_METRICS_PRODUCERS")
+)
 
 func init() {
 	RegisterMetricReader("otlp", func(ctx context.Context) (metric.Reader, error) {
+		producers, err := metricsProducers.create(ctx)
+		if err != nil {
+			return nil, err
+		}
+		readerOpts := []metric.PeriodicReaderOption{}
+		for _, producer := range producers {
+			readerOpts = append(readerOpts, metric.WithProducer(producer))
+		}
+
 		proto := os.Getenv(otelExporterOTLPProtoEnvKey)
 		if proto == "" {
 			proto = "http/protobuf"
@@ -86,33 +116,54 @@
 			if err != nil {
 				return nil, err
 			}
-			return metric.NewPeriodicReader(r), nil
+			return metric.NewPeriodicReader(r, readerOpts...), nil
 		case "http/protobuf":
 			r, err := otlpmetrichttp.New(ctx)
 			if err != nil {
 				return nil, err
 			}
-			return metric.NewPeriodicReader(r), nil
+			return metric.NewPeriodicReader(r, readerOpts...), nil
 		default:
 			return nil, errInvalidOTLPProtocol
 		}
 	})
 	RegisterMetricReader("console", func(ctx context.Context) (metric.Reader, error) {
+		producers, err := metricsProducers.create(ctx)
+		if err != nil {
+			return nil, err
+		}
+		readerOpts := []metric.PeriodicReaderOption{}
+		for _, producer := range producers {
+			readerOpts = append(readerOpts, metric.WithProducer(producer))
+		}
+
 		r, err := stdoutmetric.New()
 		if err != nil {
 			return nil, err
 		}
-		return metric.NewPeriodicReader(r), nil
+		return metric.NewPeriodicReader(r, readerOpts...), nil
 	})
 	RegisterMetricReader("none", func(ctx context.Context) (metric.Reader, error) {
 		return newNoopMetricReader(), nil
 	})
 	RegisterMetricReader("prometheus", func(ctx context.Context) (metric.Reader, error) {
 		// create an isolated registry instead of using the global registry --
-		// the user might not want to mix OTel with non-OTel metrics
+		// the user might not want to mix OTel with non-OTel metrics.
+		// Those that want to comingle metrics from global registry can use
+		// OTEL_METRICS_PRODUCERS=prometheus
 		reg := prometheus.NewRegistry()
 
-		reader, err := promexporter.New(promexporter.WithRegisterer(reg))
+		exporterOpts := []promexporter.Option{promexporter.WithRegisterer(reg)}
+
+		producers, err := metricsProducers.create(ctx)
+		if err != nil {
+			return nil, err
+		}
+		for _, producer := range producers {
+			exporterOpts = append(exporterOpts, promexporter.WithProducer(producer))
+		}
+
+		reader, err := promexporter.New(exporterOpts...)
 		if err != nil {
 			return nil, err
 		}
@@ -148,6 +199,13 @@
 
 		return readerWithServer{lis.Addr(), reader, &server}, nil
 	})
+
+	RegisterMetricProducer("prometheus", func(ctx context.Context) (metric.Producer, error) {
+		return prometheusbridge.NewMetricProducer(), nil
+	})
+	RegisterMetricProducer("none", func(ctx context.Context) (metric.Producer, error) {
+		return newNoopMetricProducer(), nil
+	})
 }
 
 type readerWithServer struct {
@@ -170,3 +228,61 @@
 	}
 	return result
 }
+
+type producerRegistry struct {
+	envKey           string
+	fallbackProducer func(context.Context) (metric.Producer, error)
+	registry         *registry[metric.Producer]
+}
+
+func newProducerRegistry(envKey string) producerRegistry {
+	return producerRegistry{
+		envKey: envKey,
+		registry: &registry[metric.Producer]{
+			names: make(map[string]func(context.Context) (metric.Producer, error)),
+		},
+	}
+}
+
+func (pr producerRegistry) create(ctx context.Context) ([]metric.Producer, error) {
+	expType := os.Getenv(pr.envKey)
+	if expType == "" {
+		if pr.fallbackProducer != nil {
+			producer, err := pr.fallbackProducer(ctx)
+			if err != nil {
+				return nil, err
+			}
+
+			return []metric.Producer{producer}, nil
+		}
+
+		return nil, nil
+	}
+
+	producers := dedupedMetricProducers(expType)
+	metricProducers := make([]metric.Producer, 0, len(producers))
+	for _, producer := range producers {
+		producer, err := pr.registry.load(ctx, producer)
+		if err != nil {
+			return nil, err
+		}
+
+		metricProducers = append(metricProducers, producer)
+	}
+
+	return metricProducers, nil
+}
+
+func dedupedMetricProducers(envValue string) []string {
+	producers := make(map[string]struct{})
+	for _, producer := range strings.Split(envValue, ",") {
+		producers[producer] = struct{}{}
+	}
+
+	result := make([]string, 0, len(producers))
+	for producer := range producers {
+		result = append(result, producer)
+	}
+
+	return result
+}