Add a default build configuration to ocb.

Embed the build configuration that is used to build otelcorecol into ocb
so that end users can easily generate a useful collector. This makes the
`--config` flag optional again.

Signed-off-by: James Peach <jpeach@cloudflare.com>

CHANGELOG.md

@@ -9,6 +9,7 @@
 ### 💡 Enhancements 💡
 
 - `ocb` now exits with an error if it fails to load the build configuration. (#5731)
+- `ocb` now generates a default Collector when no build configuration is supplied.
 
 ### 🧰 Bug fixes 🧰
 

Makefile

@@ -205,6 +205,7 @@ genotelcorecol:
 
 .PHONY: ocb
 ocb:
+	$(MAKE) -C cmd/builder config
 	$(MAKE) -C cmd/builder ocb
 
 DEPENDABOT_PATH=".github/dependabot.yml"
@@ -397,6 +398,7 @@ endif
 	sed -i.bak 's/$(PREVIOUS_VERSION)/$(RELEASE_CANDIDATE)/g' examples/k8s/otel-config.yaml
 	find . -name "*.bak" -type f -delete
 	# regenerate files
+	$(MAKE) -C cmd/builder config
 	$(MAKE) genotelcorecol
 	# commit changes before running multimod
 	git checkout -b opentelemetry-collector-bot/release-$(RELEASE_CANDIDATE)

cmd/builder/Makefile

@@ -3,3 +3,12 @@ include ../../Makefile.Common
 .PHONY: ocb
 ocb:
 	GO111MODULE=on CGO_ENABLED=0 $(GOCMD) build -trimpath -o ../../bin/ocb_$(GOOS)_$(GOARCH) .
+
+# Generate the default build config from otelcorecol, by removing the
+# "replaces" stanza, which is assumed to be at the end of the file.
+#
+# The default config file is checked in so that `go install` will work
+# and so that non-unix builds don't need sed to be installed.
+.PHONY: config
+config: internal/config/default.yaml
+	sed '-e/replaces:/,$$d' <../otelcorecol/builder-config.yaml > internal/config/default.yaml

cmd/builder/internal/command.go

@@ -27,6 +27,7 @@ import (
 	"go.uber.org/zap"
 
 	"go.opentelemetry.io/collector/cmd/builder/internal/builder"
+	"go.opentelemetry.io/collector/cmd/builder/internal/config"
 )
 
 var (
@@ -44,7 +45,8 @@ func Command() (*cobra.Command, error) {
 		Long: fmt.Sprintf("OpenTelemetry Collector Builder (%s)", version) + `
 
 ocb generates a custom OpenTelemetry Collector binary using the
-build configuration given by the "--config" argument.
+build configuration given by the "--config" argument. If no build
+configuration is provided, ocb will generate a default Collector.
 `,
 		Args: cobra.NoArgs,
 		RunE: func(cmd *cobra.Command, args []string) error {
@@ -65,13 +67,6 @@ build configuration given by the "--config" argument.
 
 	cmd.Flags().StringVar(&cfgFile, "config", "", "build configuration file")
 
-	// A build configuration file is always required, and there's no
-	// default. We can relax this in future by embedding the default
-	// config that is used to build otelcorecol.
-	if err := cmd.MarkFlagRequired("config"); err != nil {
-		panic(err) // Only fails if the usage message is empty, which is a programmer error.
-	}
-
 	// the distribution parameters, which we accept as CLI flags as well
 	cmd.Flags().BoolVar(&cfg.SkipCompilation, "skip-compilation", false, "Whether builder should only generate go code with no compile of the collector (default false)")
 	cmd.Flags().StringVar(&cfg.Distribution.Name, "name", "otelcol-custom", "The executable name for the OpenTelemetry Collector distribution")
@@ -96,8 +91,18 @@ func initConfig() error {
 	cfg.Logger.Info("OpenTelemetry Collector Builder",
 		zap.String("version", version), zap.String("date", date))
 
-	// load the config file
-	if err := k.Load(file.Provider(cfgFile), yaml.Parser()); err != nil {
+	var provider koanf.Provider
+
+	if cfgFile != "" {
+		// load the config file
+		provider = file.Provider(cfgFile)
+	} else {
+		// or the default if the config isn't provided
+		provider = config.DefaultProvider()
+		cfg.Logger.Info("Using default build configuration")
+	}
+
+	if err := k.Load(provider, yaml.Parser()); err != nil {
 		return fmt.Errorf("failed to load configuration file: %w", err)
 	}
 
@@ -112,6 +117,9 @@ func initConfig() error {
 		return fmt.Errorf("failed to unmarshal configuration: %w", err)
 	}
 
-	cfg.Logger.Info("Using config file", zap.String("path", cfgFile))
+	if cfgFile != "" {
+		cfg.Logger.Info("Using config file", zap.String("path", cfgFile))
+	}
+
 	return nil
 }

cmd/builder/internal/config/default.go

@@ -0,0 +1,32 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package config
+
+import (
+	"embed"
+
+	"github.com/knadh/koanf"
+	"github.com/knadh/koanf/providers/fs"
+)
+
+//go:embed *.yaml
+var configs embed.FS
+
+// DefaultProvider returns a koanf.Provider that provides the default build
+// configuration file. This is the same configuration that otelcorecol is
+// built with.
+func DefaultProvider() koanf.Provider {
+	return fs.Provider(configs, "default.yaml")
+}

cmd/builder/internal/config/default.yaml

@@ -0,0 +1,28 @@
+dist:
+  module: go.opentelemetry.io/collector/cmd/otelcorecol
+  name: otelcorecol
+  description: Local OpenTelemetry Collector binary, testing only.
+  version: 0.56.0-dev
+  otelcol_version: 0.56.0
+
+receivers:
+  - import: go.opentelemetry.io/collector/receiver/otlpreceiver
+    gomod: go.opentelemetry.io/collector v0.56.0
+exporters:
+  - import: go.opentelemetry.io/collector/exporter/loggingexporter
+    gomod: go.opentelemetry.io/collector v0.56.0
+  - import: go.opentelemetry.io/collector/exporter/otlpexporter
+    gomod: go.opentelemetry.io/collector v0.56.0
+  - import: go.opentelemetry.io/collector/exporter/otlphttpexporter
+    gomod: go.opentelemetry.io/collector v0.56.0
+extensions:
+  - import: go.opentelemetry.io/collector/extension/ballastextension
+    gomod: go.opentelemetry.io/collector v0.56.0
+  - import: go.opentelemetry.io/collector/extension/zpagesextension
+    gomod: go.opentelemetry.io/collector v0.56.0
+processors:
+  - import: go.opentelemetry.io/collector/processor/batchprocessor
+    gomod: go.opentelemetry.io/collector v0.56.0
+  - import: go.opentelemetry.io/collector/processor/memorylimiterprocessor
+    gomod: go.opentelemetry.io/collector v0.56.0
+