fix(influxd): add print-config subcommand to support automation

cmd/influxd/launcher/cmd.go

@@ -31,6 +31,7 @@ const (
 // The `run` subcommand is set as the default to execute.
 func NewInfluxdCommand(ctx context.Context, v *viper.Viper) *cobra.Command {
 	o := newOpts(v)
+	cliOpts := o.bindCliOpts()
 
 	prog := cli.Program{
 		Name: "influxd",
@@ -45,9 +46,10 @@ func NewInfluxdCommand(ctx context.Context, v *viper.Viper) *cobra.Command {
 	}
 	for _, c := range []*cobra.Command{cmd, runCmd} {
 		setCmdDescriptions(c)
-		o.bindCliOpts(c)
+		cli.BindOptions(o.Viper, c, cliOpts)
 	}
 	cmd.AddCommand(runCmd)
+	cmd.AddCommand(NewInfluxdPrintConfigCommand(v, cliOpts))
 
 	return cmd
 }
@@ -182,9 +184,10 @@ func newOpts(viper *viper.Viper) *InfluxdOpts {
 	}
 }
 
-// bindCliOpts configures a cobra command to set server options based on CLI args.
-func (o *InfluxdOpts) bindCliOpts(cmd *cobra.Command) {
-	opts := []cli.Opt{
+// bindCliOpts returns a list of options which can be added to a cobra command
+// in order to set options over the CLI.
+func (o *InfluxdOpts) bindCliOpts() []cli.Opt {
+	return []cli.Opt{
 		{
 			DestP:   &o.LogLevel,
 			Flag:    "log-level",
@@ -470,6 +473,4 @@ func (o *InfluxdOpts) bindCliOpts(cmd *cobra.Command) {
 			Desc:  "The maximum number of group by time bucket a SELECT can create. A value of zero will max the maximum number of buckets unlimited.",
 		},
 	}
-
-	cli.BindOptions(o.Viper, cmd, opts)
 }

cmd/influxd/launcher/print_config.go

@@ -0,0 +1,88 @@
+package launcher
+
+import (
+	"fmt"
+	"io"
+
+	"github.com/influxdata/influxdb/v2/kit/cli"
+	"github.com/spf13/cobra"
+	"github.com/spf13/viper"
+	"gopkg.in/yaml.v3"
+)
+
+func NewInfluxdPrintConfigCommand(v *viper.Viper, influxdOpts []cli.Opt) *cobra.Command {
+
+	var keyToPrint string
+	printOpts := make([]cli.Opt, len(influxdOpts)+1)
+
+	printOpts[0] = cli.Opt{
+		DestP: &keyToPrint,
+		Flag:  "key-name",
+		Desc:  "config key name; if set, only the resolved value of that key will be printed",
+	}
+	for i, opt := range influxdOpts {
+		printOpts[i+1] = cli.Opt{
+			DestP:  opt.DestP,
+			Flag:   opt.Flag,
+			Hidden: true,
+		}
+	}
+
+	cmd := &cobra.Command{
+		Use:   "print-config",
+		Short: "Print the full influxd config resolved from the current environment",
+		Long: `
+Print config (in YAML) that the influxd server would use if run with the current flags/env vars/config file.
+
+The order of precedence for config options are as follows (1 highest, 3 lowest):
+	1. flags
+	2. env vars
+	3. config file
+
+A config file can be provided via the INFLUXD_CONFIG_PATH env var. If a file is
+not provided via an env var, influxd will look in the current directory for a
+config.{json|toml|yaml|yml} file. If one does not exist, then it will continue unchanged.
+
+See 'influxd -h' for the full list of config options supported by the server.
+`,
+		RunE: func(cmd *cobra.Command, _ []string) error {
+			var err error
+			if keyToPrint == "" {
+				err = printAllConfigRunE(printOpts, cmd.OutOrStdout())
+			} else {
+				err = printOneConfigRunE(printOpts, keyToPrint, cmd.OutOrStdout())
+			}
+
+			if err != nil {
+				return fmt.Errorf("failed to print config: %w", err)
+			}
+
+			return nil
+		},
+		Args: cobra.NoArgs,
+	}
+	cli.BindOptions(v, cmd, printOpts)
+
+	return cmd
+}
+
+func printAllConfigRunE(configOpts []cli.Opt, out io.Writer) error {
+	configMap := make(map[string]interface{}, len(configOpts))
+
+	for _, o := range configOpts {
+		configMap[o.Flag] = o.DestP
+	}
+
+	return yaml.NewEncoder(out).Encode(configMap)
+}
+
+func printOneConfigRunE(configOpts []cli.Opt, key string, out io.Writer) error {
+	for _, o := range configOpts {
+		if o.Flag != key {
+			continue
+		}
+		return yaml.NewEncoder(out).Encode(o.DestP)
+	}
+
+	return fmt.Errorf("key %q not found in config", key)
+}

cmd/influxd/launcher/print_config_test.go

@@ -0,0 +1,130 @@
+package launcher
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/influxdata/influxdb/v2"
+	"github.com/influxdata/influxdb/v2/kit/cli"
+	"github.com/stretchr/testify/require"
+	"go.uber.org/zap/zapcore"
+)
+
+// Pretend we've already used cobra/viper to write
+// values into these vars.
+var stringVar = "string-value"
+var intVar = 12344
+var boolVar = false
+var floatVar = 987.654
+var sliceVar = []string{"hello", "world"}
+var mapVar = map[string]string{"foo": "bar", "baz": "qux"}
+var levelVar = zapcore.InfoLevel
+var idVar, _ = influxdb.IDFromString("020f755c3c082000")
+
+var opts = []cli.Opt{
+	{
+		DestP: &stringVar,
+		Flag:  "string-var",
+	},
+	{
+		DestP: &intVar,
+		Flag:  "int-var",
+	},
+	{
+		DestP: &boolVar,
+		Flag:  "bool-var",
+	},
+	{
+		DestP: &floatVar,
+		Flag:  "float-var",
+	},
+	{
+		DestP: &sliceVar,
+		Flag:  "slice-var",
+	},
+	{
+		DestP: &mapVar,
+		Flag:  "map-var",
+	},
+	{
+		DestP: &levelVar,
+		Flag:  "level-var",
+	},
+	{
+		DestP: &idVar,
+		Flag:  "id-var",
+	},
+}
+
+func Test_printAllConfig(t *testing.T) {
+	var out bytes.Buffer
+	require.NoError(t, printAllConfigRunE(opts, &out))
+
+	expected := `bool-var: false
+float-var: 987.654
+id-var: 020f755c3c082000
+int-var: 12344
+level-var: info
+map-var:
+    baz: qux
+    foo: bar
+slice-var:
+  - hello
+  - world
+string-var: string-value
+`
+
+	require.Equal(t, expected, out.String())
+}
+
+func Test_printOneConfig(t *testing.T) {
+	testCases := []struct {
+		key      string
+		expected string
+	}{
+		{
+			key:      "bool-var",
+			expected: "false",
+		},
+		{
+			key:      "float-var",
+			expected: "987.654",
+		},
+		{
+			key:      "id-var",
+			expected: "020f755c3c082000",
+		},
+		{
+			key:      "level-var",
+			expected: "info",
+		},
+		{
+			key: "map-var",
+			expected: `baz: qux
+foo: bar`,
+		},
+		{
+			key: "slice-var",
+			expected: `- hello
+- world`,
+		},
+		{
+			key:      "string-var",
+			expected: "string-value",
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.key, func(t *testing.T) {
+			var out bytes.Buffer
+			require.NoError(t, printOneConfigRunE(opts, tc.key, &out))
+			require.Equal(t, tc.expected+"\n", out.String())
+		})
+	}
+
+	t.Run("bad-key", func(t *testing.T) {
+		var out bytes.Buffer
+		require.Error(t, printOneConfigRunE(opts, "bad-key", &out))
+		require.Empty(t, out.String())
+	})
+}