feat(builder): user_data attribute

.web-docs/components/builder/instance/README.md

@@ -90,6 +90,15 @@ The configuration arguments for the builder. Arguments can either be required or
   for testing provisioner logic without incurring the cost of image creation.
   Defaults to `false`.
 
+- `user_data` (string) - User data for instance initialization systems such as cloud-init. The
+  value is a UTF-8 string and will be Base64-encoded by the plugin before
+  transmission. The maximum size is 32 KiB, measured before encoding. Use
+  Packer's built-in functions such as `file` to read content from disk.
+  Packer does not wait for user data to finish executing before shutting
+  down the instance. If your user data must complete before the image is
+  created, run `cloud-init status --wait` or an equivalent in a
+  provisioner.
+
 <!-- End of code generated from the comments of the Config struct in component/builder/instance/config.go; -->
 
 

component/builder/instance/config.go

@@ -103,6 +103,16 @@ type Config struct {
 	// Defaults to `false`.
 	SkipCreateImage bool `mapstructure:"skip_create_image" required:"false"`
 
+	// User data for instance initialization systems such as cloud-init. The
+	// value is a UTF-8 string and will be Base64-encoded by the plugin before
+	// transmission. The maximum size is 32 KiB, measured before encoding. Use
+	// Packer's built-in functions such as `file` to read content from disk.
+	// Packer does not wait for user data to finish executing before shutting
+	// down the instance. If your user data must complete before the image is
+	// created, run `cloud-init status --wait` or an equivalent in a
+	// provisioner.
+	UserData string `mapstructure:"user_data" required:"false"`
+
 	ctx interpolate.Context
 }
 
@@ -199,6 +209,13 @@ func (c *Config) Prepare(args ...any) ([]string, error) {
 			)
 		}
 
+		if len(c.UserData) > 32*1024 {
+			multiErr = packer.MultiErrorAppend(
+				multiErr,
+				errors.New("user_data must be 32 KiB or less of unencoded data"),
+			)
+		}
+
 		if multiErr != nil && len(multiErr.Errors) > 0 {
 			return nil, multiErr
 		}

component/builder/instance/step_instance_create.go

@@ -6,6 +6,7 @@ package instance
 
 import (
 	"context"
+	"encoding/base64"
 	"fmt"
 	"time"
 
@@ -111,6 +112,12 @@ func (o *stepInstanceCreate) Run(
 
 				return res
 			}(config.SSHPublicKeys),
+			UserData: func(userData string) string {
+				if userData == "" {
+					return ""
+				}
+				return base64.StdEncoding.EncodeToString([]byte(userData))
+			}(config.UserData),
 		},
 	})
 	if err != nil {

docs-partials/component/builder/instance/Config-not-required.mdx

@@ -51,4 +51,13 @@
   for testing provisioner logic without incurring the cost of image creation.
   Defaults to `false`.
 
+- `user_data` (string) - User data for instance initialization systems such as cloud-init. The
+  value is a UTF-8 string and will be Base64-encoded by the plugin before
+  transmission. The maximum size is 32 KiB, measured before encoding. Use
+  Packer's built-in functions such as `file` to read content from disk.
+  Packer does not wait for user data to finish executing before shutting
+  down the instance. If your user data must complete before the image is
+  created, run `cloud-init status --wait` or an equivalent in a
+  provisioner.
+
 <!-- End of code generated from the comments of the Config struct in component/builder/instance/config.go; -->