Change default otlp exporter GRPC load balancer to round robin (#10319)

#### Description
Updates the default `pick_first` load balancer to `round_robin`, which
allows for better resource allocation and less chances of throttling
data being sent to addresses.

#### Link to tracking issue
Fixes #10298 (has full context of this PR)

#### Testing
Edited tests to allow round_robin load balancing.

---------

Co-authored-by: Alex Boten <223565+codeboten@users.noreply.github.com>
Co-authored-by: Juraci Paixão Kröhling <juraci.github@kroehling.de>

.chloggen/load-balancer-round-robin.yaml

@@ -0,0 +1,24 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: configgrpc
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Update the default load balancer strategy to round_robin
+
+# One or more tracking issues or pull requests related to the change
+issues: [10319]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext: To restore the behavior that was previously the default, set `balancer_name` to `pick_first`.
+
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+change_logs: [user]

config/configgrpc/README.md

@@ -15,8 +15,8 @@ configuration parameters are also defined under `tls` like server
 configuration. For more information, see [configtls
 README](../configtls/README.md).
 
-- [`balancer_name`](https://github.com/grpc/grpc-go/blob/master/examples/features/load_balancing/README.md)
-- `compression` Compression type to use among `gzip`, `snappy`, `zstd`, and `none`.
+- [`balancer_name`](https://github.com/grpc/grpc-go/blob/master/examples/features/load_balancing/README.md): Default before v0.103.0 is `pick_first`, default for v0.103.0 is `round_robin`. See [issue](https://github.com/open-telemetry/opentelemetry-collector/issues/10298). To restore the previous behavior, set `balancer_name` to `pick_first`.
+- `compression`: Compression type to use among `gzip`, `snappy`, `zstd`, and `none`.
 - `endpoint`: Valid value syntax available [here](https://github.com/grpc/grpc/blob/master/doc/naming.md)
 - [`tls`](../configtls/README.md)
 - `headers`: name/value pairs added to the request

config/configgrpc/configgrpc.go

@@ -55,6 +55,11 @@ func NewDefaultKeepaliveClientConfig() *KeepaliveClientConfig {
 	}
 }
 
+// BalancerName returns a string with default load balancer value
+func BalancerName() string {
+	return "round_robin"
+}
+
 // ClientConfig defines common settings for a gRPC client configuration.
 type ClientConfig struct {
 	// The target to which the exporter is going to send traces or metrics,
@@ -102,9 +107,10 @@ type ClientConfig struct {
 // NewDefaultClientConfig returns a new instance of ClientConfig with default values.
 func NewDefaultClientConfig() *ClientConfig {
 	return &ClientConfig{
-		TLSSetting: configtls.NewDefaultClientConfig(),
-		Keepalive:  NewDefaultKeepaliveClientConfig(),
-		Auth:       configauth.NewDefaultAuthentication(),
+		TLSSetting:   configtls.NewDefaultClientConfig(),
+		Keepalive:    NewDefaultKeepaliveClientConfig(),
+		Auth:         configauth.NewDefaultAuthentication(),
+		BalancerName: BalancerName(),
 	}
 }
 

config/configgrpc/configgrpc_test.go

@@ -48,9 +48,10 @@ func TestNewDefaultKeepaliveClientConfig(t *testing.T) {
 
 func TestNewDefaultClientConfig(t *testing.T) {
 	expected := &ClientConfig{
-		TLSSetting: configtls.NewDefaultClientConfig(),
-		Keepalive:  NewDefaultKeepaliveClientConfig(),
-		Auth:       configauth.NewDefaultAuthentication(),
+		TLSSetting:   configtls.NewDefaultClientConfig(),
+		Keepalive:    NewDefaultKeepaliveClientConfig(),
+		Auth:         configauth.NewDefaultAuthentication(),
+		BalancerName: BalancerName(),
 	}
 
 	result := NewDefaultClientConfig()
@@ -215,7 +216,7 @@ func TestAllGrpcClientSettings(t *testing.T) {
 				ReadBufferSize:  1024,
 				WriteBufferSize: 1024,
 				WaitForReady:    true,
-				BalancerName:    "configgrpc_balancer_test",
+				BalancerName:    "round_robin",
 				Authority:       "pseudo-authority",
 				Auth:            &configauth.Authentication{AuthenticatorID: testAuthID},
 			},