Restrict scrape timeout to interval length

config/config.go

@@ -266,6 +266,9 @@ func (c *Config) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		if scfg.ScrapeTimeout == 0 {
 			scfg.ScrapeTimeout = c.GlobalConfig.ScrapeTimeout
 		}
+		if scfg.ScrapeTimeout > scfg.ScrapeInterval {
+			return fmt.Errorf("scrape timeout greater than scrape interval for scrape config with job name %q", scfg.JobName)
+		}
 
 		if _, ok := jobNames[scfg.JobName]; ok {
 			return fmt.Errorf("found multiple scrape configs with job name %q", scfg.JobName)

config/config_test.go

@@ -335,6 +335,9 @@ var expectedErrors = []struct {
 	}, {
 		filename: "jobname_dup.bad.yml",
 		errMsg:   `found multiple scrape configs with job name "prometheus"`,
+	}, {
+		filename: "scrape_interval.bad.yml",
+		errMsg:   `scrape timeout greater than scrape interval`,
 	}, {
 		filename: "labelname.bad.yml",
 		errMsg:   `"not$allowed" is not a valid label name`,

config/testdata/scrape_interval.bad.yml

@@ -0,0 +1,4 @@
+scrape_configs:
+- job_name: prometheus
+  scrape_interval: 5s
+  scrape_timeout:  6s