Make sure that url for remote_read/write is not nil (#3024)

config/config.go

@@ -1404,7 +1404,7 @@ func (re Regexp) MarshalYAML() (interface{}, error) {
 
 // RemoteWriteConfig is the configuration for writing to remote storage.
 type RemoteWriteConfig struct {
-	URL                 *URL             `yaml:"url,omitempty"`
+	URL                 *URL             `yaml:"url"`
 	RemoteTimeout       model.Duration   `yaml:"remote_timeout,omitempty"`
 	WriteRelabelConfigs []*RelabelConfig `yaml:"write_relabel_configs,omitempty"`
 
@@ -1424,6 +1424,9 @@ func (c *RemoteWriteConfig) UnmarshalYAML(unmarshal func(interface{}) error) err
 	if err := unmarshal((*plain)(c)); err != nil {
 		return err
 	}
+	if c.URL == nil {
+		return fmt.Errorf("url for remote_write is empty")
+	}
 
 	// The UnmarshalYAML method of HTTPClientConfig is not being called because it's not a pointer.
 	// We cannot make it a pointer as the parser panics for inlined pointer structs.
@@ -1463,7 +1466,7 @@ type QueueConfig struct {
 
 // RemoteReadConfig is the configuration for reading from remote storage.
 type RemoteReadConfig struct {
-	URL           *URL           `yaml:"url,omitempty"`
+	URL           *URL           `yaml:"url"`
 	RemoteTimeout model.Duration `yaml:"remote_timeout,omitempty"`
 
 	// We cannot do proper Go type embedding below as the parser will then parse
@@ -1481,6 +1484,9 @@ func (c *RemoteReadConfig) UnmarshalYAML(unmarshal func(interface{}) error) erro
 	if err := unmarshal((*plain)(c)); err != nil {
 		return err
 	}
+	if c.URL == nil {
+		return fmt.Errorf("url for remote_read is empty")
+	}
 
 	// The UnmarshalYAML method of HTTPClientConfig is not being called because it's not a pointer.
 	// We cannot make it a pointer as the parser panics for inlined pointer structs.

config/config_test.go

@@ -668,6 +668,12 @@ var expectedErrors = []struct {
 	}, {
 		filename: "unknown_global_attr.bad.yml",
 		errMsg:   "unknown fields in global config: nonexistent_field",
+	}, {
+		filename: "remote_read_url_missing.bad.yml",
+		errMsg:   `url for remote_read is empty`,
+	}, {
+		filename: "remote_write_url_missing.bad.yml",
+		errMsg:   `url for remote_write is empty`,
 	},
 }
 

config/testdata/remote_read_url_missing.bad.yml

+remote_read:
+  - url:

config/testdata/remote_write_url_missing.bad.yml

+remote_write:
+  - url: