Only error if errors are more than 4% of all requests.

 🐿 v2.5.16

package.json

@@ -23,7 +23,7 @@
     "next-metrics": "^1.16.1"
   },
   "devDependencies": {
-    "@financial-times/n-gage": "^1.9.5",
+    "@financial-times/n-gage": "^1.14.0",
     "body-parser": "^1.15.0",
     "chai": "^3.0.0",
     "coveralls": "^2.11.16",

src/lib/error-rate-check.js

@@ -7,13 +7,14 @@ module.exports = (appName, opts) => {
 	const severity = opts.severity || DEFAULT_SEVERITY;
 	let region = process.env.REGION ? '_' + process.env.REGION : '';
 	return nHealth.runCheck({
-		name: `The error rate for ${appName} is acceptable`,
-		type: 'graphiteSpike',
-		numerator: `next.heroku.${appName}.web_*${region}.express.*.res.status.{500,503,504}.count`,
-		divisor: `next.heroku.${appName}.web_*${region}.express.*.res.status.*.count`,
+		name: `The error rate for ${appName} is greater than 4% of requests`,
+		type: 'graphiteThreshold',
+		metric: `asPercent(summarize(sumSeries(next.heroku.${appName}.web_*${region}.express.*.res.status.{500,503,504}.count), '10min', 'sum', true), summarize(sumSeries(next.heroku.${appName}.web_*${region}.express.*.res.status.*.count), '10min', 'sum', true))`,
+		threshold: 4,
+		samplePeriod: '10min',
 		severity,
 		businessImpact: 'Users may see application error pages.',
-		technicalSummary: `The proportion of 500 responses for the ${appName} app is 3 times higher in the last 10 minutes than the error rate over the previous 7 days. This is a default n-express check.`,
+		technicalSummary: `The proportion of error responses for ${appName} is greater than 4% of all responses. This is a default n-express check.`,
 		panicGuide: 'Consult errors in sentry, application logs in splunk and run the application locally to identify errors'
 	});
 };

test/app/error-rate-check.test.js

@@ -28,27 +28,22 @@ describe('Default error rate check', () => {
 	it('should compose correct graphite metric with region', () => {
 		process.env.REGION = 'US';
 
-		const expectedNumerator = 'next.heroku.app-name.web_*_US.express.*.res.status.{500,503,504}.count';
-		const expectedDivisor = 'next.heroku.app-name.web_*_US.express.*.res.status.*.count';
+		const metric = 'asPercent(summarize(sumSeries(next.heroku.app-name.web_*_US.express.*.res.status.{500,503,504}.count), \'10min\', \'sum\', true), summarize(sumSeries(next.heroku.app-name.web_*_US.express.*.res.status.*.count), \'10min\', \'sum\', true))';
 
 		subject('app-name');
 		expect(nHealthStub.runCheck).calledWithMatch({
-			numerator: expectedNumerator,
-			divisor: expectedDivisor
+			metric
 		});
 	});
 
 	it('should compose correct graphite metric without region', () => {
 		delete process.env.REGION;
 
-		const expectedNumerator = 'next.heroku.app-name.web_*.express.*.res.status.{500,503,504}.count';
-		const expectedDivisor = 'next.heroku.app-name.web_*.express.*.res.status.*.count';
+		const metric = 'asPercent(summarize(sumSeries(next.heroku.app-name.web_*.express.*.res.status.{500,503,504}.count), \'10min\', \'sum\', true), summarize(sumSeries(next.heroku.app-name.web_*.express.*.res.status.*.count), \'10min\', \'sum\', true))';
 
 		subject('app-name');
-
 		expect(nHealthStub.runCheck).calledWithMatch({
-			numerator: expectedNumerator,
-			divisor: expectedDivisor
+			metric
 		});
 	});