feat(*): warn on encountering unrecognized keys in cloud-config

initialize/config.go

@@ -43,10 +43,35 @@ type CloudConfig struct {
 	ManageEtcHosts EtcHosts `yaml:"manage_etc_hosts"`
 }
 
+type warner func(format string, v ...interface{})
+
+func warnOnUnrecognizedKeys(contents string, warn warner) {
+	// Generate a map of all understood cloud config options
+	var cc map[string]interface{}
+	b, _ := goyaml.Marshal(&CloudConfig{})
+	goyaml.Unmarshal(b, &cc)
+	// Now unmarshal the entire provided contents
+	var c map[string]interface{}
+	goyaml.Unmarshal([]byte(contents), &c)
+	// Check that every key in the contents exists in the cloud config
+	for k, _ := range c {
+		if _, ok := cc[k]; !ok {
+			warn("Warning: unrecognized key %q in provided cloud config - ignoring section", k)
+		}
+	}
+}
+
+// NewCloudConfig instantiates a new CloudConfig from the given contents (a
+// string of YAML), returning any error encountered. It will ignore unknown
+// fields but log encountering them.
 func NewCloudConfig(contents string) (*CloudConfig, error) {
 	var cfg CloudConfig
 	err := goyaml.Unmarshal([]byte(contents), &cfg)
+	if err != nil {
 		return &cfg, err
+	}
+	warnOnUnrecognizedKeys(contents, log.Printf)
+	return &cfg, nil
 }
 
 func (cc CloudConfig) String() string {

initialize/config_test.go

@@ -1,10 +1,50 @@
 package initialize
 
 import (
+	"fmt"
 	"strings"
 	"testing"
 )
 
+func TestCloudConfigUnknownKeys(t *testing.T) {
+	contents := `
+coreos: 
+  etcd:
+    discovery: "https://discovery.etcd.io/827c73219eeb2fa5530027c37bf18877"
+unknown:
+  dunno:
+    something
+foo:
+  bar
+hostname:
+  foo
+`
+	cfg, err := NewCloudConfig(contents)
+	if err != nil {
+		t.Fatalf("error instantiating CloudConfig with unknown keys: %v", err)
+	}
+	if cfg.Hostname != "foo" {
+		t.Fatalf("hostname not correctly set when invalid keys are present")
+	}
+	if len(cfg.Coreos.Etcd) < 1 {
+		t.Fatalf("etcd section not correctly set when invalid keys are present")
+	}
+
+	var warnings string
+	catchWarn := func(f string, v ...interface{}) {
+		warnings += fmt.Sprintf(f, v...)
+	}
+
+	warnOnUnrecognizedKeys(contents, catchWarn)
+
+	if !strings.Contains(warnings, "foo") {
+		t.Errorf("warnings did not catch unrecognized key foo")
+	}
+	if !strings.Contains(warnings, "unknown") {
+		t.Errorf("warnings did not catch unrecognized key unknown")
+	}
+}
+
 // Assert that the parsing of a cloud config file "generally works"
 func TestCloudConfigEmpty(t *testing.T) {
 	cfg, err := NewCloudConfig("")