Merge pull request #1389 from marmijo/marmijo_issue_1339

units: Sort systemd presets in alphabetical order in 20-ignition.preset file

internal/exec/stages/files/units.go

@@ -18,6 +18,7 @@ import (
 	"context"
 	"fmt"
 	"path/filepath"
+	"sort"
 	"strings"
 
 	"github.com/coreos/ignition/v2/config/shared/errors"
@@ -151,7 +152,17 @@ func (s *stage) createSystemdPresetFile(presets map[string]*Preset) error {
 		return err
 	}
 	hasInstanceUnit := false
-	for _, value := range presets {
+
+	// sort the units before writing to the systemd presets file to ensure
+	// the file is written in a consistent order across multiple runs
+	unitNames := make([]string, 0, len(presets))
+	for unit := range presets {
+		unitNames = append(unitNames, unit)
+	}
+	sort.Strings(unitNames)
+
+	for _, name := range unitNames {
+		value := presets[name]
 		unitString := value.unit
 		if value.instantiatable {
 			hasInstanceUnit = true

tests/positive/files/units.go

@@ -25,6 +25,7 @@ func init() {
 	register.Register(register.PositiveTest, TestUnmaskUnit())
 	register.Register(register.PositiveTest, TestMaskUnit())
 	register.Register(register.PositiveTest, RemoveEnablementSymLinksforUnit())
+	register.Register(register.PositiveTest, TestPresetsFileInAlphabeticalOrder())
 }
 
 func CreateInstantiatedService() types.Test {
@@ -320,3 +321,57 @@ func RemoveEnablementSymLinksforUnit() types.Test {
 		ConfigMinVersion: configMinVersion,
 	}
 }
+
+// TestPresetsFileinAlphabeticalOrder checks if Ignition
+// writes the systemd presets in alphabetical order by
+// unit name into the 20-ignition.preset file.
+func TestPresetsFileInAlphabeticalOrder() types.Test {
+	name := "unit.presets.sorted"
+	in := types.GetBaseDisk()
+	out := types.GetBaseDisk()
+	config := `{
+		"ignition": { "version": "$version" },
+		"systemd": {
+			"units": [
+				{
+					"enabled": true,
+					"name": "foo.service"
+				},
+				{
+					"enabled": true,
+					"name": "bar.service"
+				},
+				{
+					"enabled": true,
+					"name": "qux.service"
+				},
+				{
+					"enabled": true,
+					"name": "baz.service"
+				},
+				{
+					"enabled": true,
+					"name": "garply.service"
+				}
+			]
+        }
+		}`
+	out[0].Partitions.AddFiles("ROOT", []types.File{
+		{
+			Node: types.Node{
+				Name:      "20-ignition.preset",
+				Directory: "etc/systemd/system-preset",
+			},
+			Contents: "enable bar.service\nenable baz.service\nenable foo.service\nenable garply.service\nenable qux.service\n",
+		},
+	})
+	configMinVersion := "3.0.0"
+
+	return types.Test{
+		Name:             name,
+		In:               in,
+		Out:              out,
+		Config:           config,
+		ConfigMinVersion: configMinVersion,
+	}
+}