cmd: ability to override settings with environment variables

cmd/serve.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io/ioutil"
 	netHTTP "net/http"
+	"os"
 	"runtime"
 	"strings"
 
@@ -94,15 +95,40 @@ and exports them to Kafka.`,
 			DecodeHook: mapstructure.ComposeDecodeHookFunc(
 				mapstructure.TextUnmarshallerHookFunc(),
 				mapstructure.StringToTimeDurationHookFunc(),
+				mapstructure.StringToSliceHookFunc(","),
 			),
 		})
 		if err != nil {
 			return fmt.Errorf("unable to create configuration decoder: %w", err)
 		}
-		if decoder.Decode(rawConfig); err != nil {
+		if err := decoder.Decode(rawConfig); err != nil {
 			return fmt.Errorf("unable to parse configuration: %w", err)
 		}
 
+		// Override with environment variables
+		for _, keyval := range os.Environ() {
+			kv := strings.SplitN(keyval, "=", 2)
+			if len(kv) != 2 {
+				continue
+			}
+			kk := strings.Split(kv[0], "_")
+			if kk[0] != "AKVORADO" || len(kk) < 2 {
+				continue
+			}
+			// From AKVORADO_SQUID_PURPLE_QUIRK=47, we
+			// build a map "squid -> purple -> quirk -> 47"
+			var rawConfig interface{}
+			rawConfig = kv[1]
+			for i := len(kk) - 1; i > 0; i-- {
+				rawConfig = map[string]interface{}{
+					kk[i]: rawConfig,
+				}
+			}
+			if err := decoder.Decode(rawConfig); err != nil {
+				return fmt.Errorf("unable to parse override %q: %w", kv[0], err)
+			}
+		}
+
 		// Dump configuration if requested
 		if ServeOptions.dumpConfiguration {
 			output, err := yaml.Marshal(config)

cmd/serve_test.go

@@ -58,7 +58,66 @@ core:
 	cmd.ServeOptionsReset()
 	err := root.Execute()
 	if err != nil {
-		t.Errorf("`serve -D -C` error:\n%+v", err)
+		t.Fatalf("`serve -D -C` error:\n%+v", err)
+	}
+	var got cmd.ServeConfiguration
+	if err := yaml.Unmarshal(buf.Bytes(), &got); err != nil {
+		t.Fatalf("Unmarshal() error:\n%+v", err)
+	}
+	if diff := helpers.Diff(got, want); diff != "" {
+		t.Errorf("`serve -D -C` (-got, +want):\n%s", diff)
+	}
+}
+
+func TestServeEnvOverride(t *testing.T) {
+	// Configuration file
+	want := cmd.DefaultServeConfiguration
+	want.HTTP.Listen = "127.0.0.1:8000"
+	want.Flow.Listen = "0.0.0.0:2055"
+	want.Flow.Workers = 3
+	want.SNMP.Workers = 2
+	want.SNMP.CacheDuration = 1*time.Hour + 30*time.Minute
+	want.SNMP.DefaultCommunity = "privateer"
+	want.Kafka.Topic = "netflow"
+	want.Kafka.Version = kafka.Version(sarama.V2_8_1_0)
+	want.Kafka.CompressionCodec = kafka.CompressionCodec(sarama.CompressionZSTD)
+	want.Kafka.Brokers = []string{"127.0.0.1:9092", "127.0.0.2:9092"}
+	want.Core.Workers = 3
+	config := `---
+http:
+ listen: 127.0.0.1:8000
+flow:
+ listen: 0.0.0.0:2055
+ workers: 2
+snmp:
+ workers: 2
+ cache-duration: 2h
+kafka:
+ topic: netflow
+ compression-codec: zstd
+ version: 2.8.1
+core:
+ workers: 3
+`
+	configFile := filepath.Join(t.TempDir(), "akvorado.yaml")
+	ioutil.WriteFile(configFile, []byte(config), 0644)
+
+	// Environment
+	os.Setenv("AKVORADO_FLOW_WORKERS", "3")
+	os.Setenv("AKVORADO_SNMP_CACHEDURATION", "1h30m")
+	os.Setenv("AKVORADO_SNMP_DEFAULTCOMMUNITY", "privateer")
+	os.Setenv("AKVORADO_KAFKA_BROKERS", "127.0.0.1:9092,127.0.0.2:9092")
+
+	// Start serves with it
+	root := cmd.RootCmd
+	buf := new(bytes.Buffer)
+	root.SetOut(buf)
+	root.SetErr(os.Stderr)
+	root.SetArgs([]string{"serve", "-D", "-C", "--config", configFile})
+	cmd.ServeOptionsReset()
+	err := root.Execute()
+	if err != nil {
+		t.Fatalf("`serve -D -C` error:\n%+v", err)
 	}
 	var got cmd.ServeConfiguration
 	if err := yaml.Unmarshal(buf.Bytes(), &got); err != nil {

docs/configuration.md

@@ -13,9 +13,32 @@ configured through a different section:
 - `clickhouse`: [Clickhouse helper](#clickhouse)
 - `core`: [Core](#core)
 
-You can get the default configuration with `./akvorado --dump --check`.
+You can get the default configuration with `./akvorado --dump
+--check`. Durations can be written in seconds or using strings like
+`10h20m`.
 
-Durations can be written in seconds or using strings like `10h20m`.
+It is also possible to override configuration settings using
+environment variables. You need to remove any `-` from key names and
+use `_` to handle nesting. Then, put `AKVORADO_` as a prefix. For
+example, let's consider the following configuration file:
+
+```yaml
+kafka:
+  topic: test-topic
+  topic-configuration:
+    num-partitions: 1
+  brokers:
+    - 192.0.2.1:9092
+    - 192.0.2.2:9092
+```
+
+It can be translated to:
+
+```sh
+AKVORADO_KAFKA_TOPIC=test-topic
+AKVORADO_KAFKA_TOPICCONFIGURATION_NUMPARTITIONS=1
+AKVORADO_KAFKA_BROKERS=192.0.2.1:9092,192.0.2.2:9092
+```
 
 ## Reporting