config: raise error on unknown config parameters.

The YAML parser ignores additional parameters on unmarshaling. This causes
frequent confusion with bad configs that pass parsing.
These changes raise errors on additional parameters.

config/config.go

@@ -93,10 +93,24 @@ type Config struct {
 	RuleFiles     []string        `yaml:"rule_files,omitempty"`
 	ScrapeConfigs []*ScrapeConfig `yaml:"scrape_configs,omitempty"`
 
+	// Catches all undefined fields and must be empty after parsing.
+	XXX map[string]interface{} `yaml:",inline"`
+
 	// original is the input from which the config was parsed.
 	original string
 }
 
+func checkOverflow(m map[string]interface{}, ctx string) error {
+	if len(m) > 0 {
+		var keys []string
+		for k := range m {
+			keys = append(keys, k)
+		}
+		return fmt.Errorf("unknown fields in %s: %s", ctx, strings.Join(keys, ", "))
+	}
+	return nil
+}
+
 func (c Config) String() string {
 	if c.original != "" {
 		return c.original
@@ -138,7 +152,7 @@ func (c *Config) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		}
 		jobNames[scfg.JobName] = struct{}{}
 	}
-	return nil
+	return checkOverflow(c.XXX, "config")
 }
 
 // GlobalConfig configures values that are used across other configuration
@@ -150,9 +164,11 @@ type GlobalConfig struct {
 	ScrapeTimeout Duration `yaml:"scrape_timeout,omitempty"`
 	// How frequently to evaluate rules by default.
 	EvaluationInterval Duration `yaml:"evaluation_interval,omitempty"`
-
 	// The labels to add to any timeseries that this Prometheus instance scrapes.
 	Labels clientmodel.LabelSet `yaml:"labels,omitempty"`
+
+	// Catches all undefined fields and must be empty after parsing.
+	XXX map[string]interface{} `yaml:",inline"`
 }
 
 // UnmarshalYAML implements the yaml.Unmarshaler interface.
@@ -162,7 +178,7 @@ func (c *GlobalConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	if err := unmarshal((*plain)(c)); err != nil {
 		return err
 	}
-	return nil
+	return checkOverflow(c.XXX, "global config")
 }
 
 // ScrapeConfig configures a scraping unit for Prometheus.
@@ -178,7 +194,7 @@ type ScrapeConfig struct {
 	// The URL scheme with which to fetch metrics from targets.
 	Scheme string `yaml:"scheme,omitempty"`
 	// The HTTP basic authentication credentials for the targets.
-	BasicAuth *BasicAuth `yaml:"basic_auth"`
+	BasicAuth *BasicAuth `yaml:"basic_auth,omitempty"`
 
 	// List of labeled target groups for this job.
 	TargetGroups []*TargetGroup `yaml:"target_groups,omitempty"`
@@ -190,6 +206,9 @@ type ScrapeConfig struct {
 	ConsulSDConfigs []*ConsulSDConfig `yaml:"consul_sd_configs,omitempty"`
 	// List of relabel configurations.
 	RelabelConfigs []*RelabelConfig `yaml:"relabel_configs,omitempty"`
+
+	// Catches all undefined fields and must be empty after parsing.
+	XXX map[string]interface{} `yaml:",inline"`
 }
 
 // UnmarshalYAML implements the yaml.Unmarshaler interface.
@@ -203,13 +222,26 @@ func (c *ScrapeConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	if !patJobName.MatchString(c.JobName) {
 		return fmt.Errorf("%q is not a valid job name", c.JobName)
 	}
-	return nil
+	return checkOverflow(c.XXX, "scrape_config")
 }
 
 // BasicAuth contains basic HTTP authentication credentials.
 type BasicAuth struct {
 	Username string `yaml:"username"`
 	Password string `yaml:"password"`
+
+	// Catches all undefined fields and must be empty after parsing.
+	XXX map[string]interface{} `yaml:",inline"`
+}
+
+// UnmarshalYAML implements the yaml.Unmarshaler interface.
+func (a *BasicAuth) UnmarshalYAML(unmarshal func(interface{}) error) error {
+	type plain BasicAuth
+	err := unmarshal((*plain)(a))
+	if err != nil {
+		return err
+	}
+	return checkOverflow(a.XXX, "basic_auth")
 }
 
 // TargetGroup is a set of targets with a common label set.
@@ -233,6 +265,7 @@ func (tg *TargetGroup) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	g := struct {
 		Targets []string               `yaml:"targets"`
 		Labels  clientmodel.LabelSet   `yaml:"labels"`
+		XXX     map[string]interface{} `yaml:",inline"`
 	}{}
 	if err := unmarshal(&g); err != nil {
 		return err
@@ -247,7 +280,7 @@ func (tg *TargetGroup) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		})
 	}
 	tg.Labels = g.Labels
-	return nil
+	return checkOverflow(g.XXX, "target_group")
 }
 
 // MarshalYAML implements the yaml.Marshaler interface.
@@ -291,6 +324,9 @@ func (tg *TargetGroup) UnmarshalJSON(b []byte) error {
 type DNSSDConfig struct {
 	Names           []string `yaml:"names"`
 	RefreshInterval Duration `yaml:"refresh_interval,omitempty"`
+
+	// Catches all undefined fields and must be empty after parsing.
+	XXX map[string]interface{} `yaml:",inline"`
 }
 
 // UnmarshalYAML implements the yaml.Unmarshaler interface.
@@ -304,13 +340,16 @@ func (c *DNSSDConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	if len(c.Names) == 0 {
 		return fmt.Errorf("DNS-SD config must contain at least one SRV record name")
 	}
-	return nil
+	return checkOverflow(c.XXX, "dns_sd_config")
 }
 
 // FileSDConfig is the configuration for file based discovery.
 type FileSDConfig struct {
 	Names           []string `yaml:"names"`
 	RefreshInterval Duration `yaml:"refresh_interval,omitempty"`
+
+	// Catches all undefined fields and must be empty after parsing.
+	XXX map[string]interface{} `yaml:",inline"`
 }
 
 // UnmarshalYAML implements the yaml.Unmarshaler interface.
@@ -329,7 +368,7 @@ func (c *FileSDConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 			return fmt.Errorf("path name %q is not valid for file discovery", name)
 		}
 	}
-	return nil
+	return checkOverflow(c.XXX, "file_sd_config")
 }
 
 // ConsulSDConfig is the configuration for Consul service discovery.
@@ -343,6 +382,9 @@ type ConsulSDConfig struct {
 	Password     string `yaml:"password"`
 	// The list of services for which targets are discovered.
 	Services []string `yaml:"services"`
+
+	// Catches all undefined fields and must be empty after parsing.
+	XXX map[string]interface{} `yaml:",inline"`
 }
 
 // UnmarshalYAML implements the yaml.Unmarshaler interface.
@@ -359,7 +401,7 @@ func (c *ConsulSDConfig) UnmarshalYAML(unmarshal func(interface{}) error) error
 	if len(c.Services) == 0 {
 		return fmt.Errorf("Consul SD configuration requires at least one service name")
 	}
-	return nil
+	return checkOverflow(c.XXX, "consul_sd_config")
 }
 
 // RelabelAction is the action to be performed on relabeling.
@@ -403,6 +445,9 @@ type RelabelConfig struct {
 	Replacement string `yaml:"replacement,omitempty"`
 	// Action is the action to be performed for the relabeling.
 	Action RelabelAction `yaml:"action,omitempty"`
+
+	// Catches all undefined fields and must be empty after parsing.
+	XXX map[string]interface{} `yaml:",inline"`
 }
 
 // UnmarshalYAML implements the yaml.Unmarshaler interface.
@@ -415,7 +460,7 @@ func (c *RelabelConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	if c.Regex == nil {
 		return fmt.Errorf("relabel configuration requires a regular expression")
 	}
-	return nil
+	return checkOverflow(c.XXX, "relabel_config")
 }
 
 // Regexp encapsulates a regexp.Regexp and makes it YAML marshallable.

config/config_test.go

@@ -146,20 +146,20 @@ func TestLoadConfig(t *testing.T) {
 
 	c, err := LoadFromFile("testdata/conf.good.yml")
 	if err != nil {
-		t.Errorf("Error parsing %s: %s", "testdata/conf.good.yml", err)
+		t.Fatalf("Error parsing %s: %s", "testdata/conf.good.yml", err)
 	}
 	bgot, err := yaml.Marshal(c)
 	if err != nil {
-		t.Errorf("%s", err)
+		t.Fatalf("%s", err)
 	}
 	bexp, err := yaml.Marshal(expectedConf)
 	if err != nil {
-		t.Errorf("%s", err)
+		t.Fatalf("%s", err)
 	}
 	expectedConf.original = c.original
 
 	if !reflect.DeepEqual(c, expectedConf) {
-		t.Errorf("%s: unexpected config result: \n\n%s\n expected\n\n%s", "testdata/conf.good.yml", bgot, bexp)
+		t.Fatalf("%s: unexpected config result: \n\n%s\n expected\n\n%s", "testdata/conf.good.yml", bgot, bexp)
 	}
 }
 
@@ -188,6 +188,9 @@ var expectedErrors = []struct {
 	}, {
 		filename: "rules.bad.yml",
 		errMsg:   "invalid rule file path",
+	}, {
+		filename: "unknown_attr.bad.yml",
+		errMsg:   "unknown fields in scrape_config: consult_sd_configs",
 	},
 }
 

config/testdata/unknown_attr.bad.yml

@@ -0,0 +1,20 @@
+# my global config
+global:
+  scrape_interval:     15s
+  evaluation_interval: 30s
+  # scrape_timeout is set to the global default (10s).
+
+  labels:
+      monitor: codelab
+      foo:     bar
+
+rule_files:
+  - "first.rules"
+  - "second.rules"
+  - "my/*.rules"
+
+scrape_configs:
+  - job_name: prometheus
+
+    consult_sd_configs:
+    - server: 'localhost:1234'