fix(web): extend HTTP latency histogram buckets

Author: brendan-kellam

packages/web/src/httpMetrics.integration.test.ts

@@ -56,7 +56,8 @@ describe('httpMetrics', () => {
         // The finish channel fires after the response is flushed to the client.
         await new Promise(resolve => setTimeout(resolve, 100));
 
-        const counts = countLines(await registry.metrics());
+        const metrics = await registry.metrics();
+        const counts = countLines(metrics);
 
         expect(counts.some(line => line.includes('route="/api/health"'))).toBe(true);
         expect(counts.some(line => line.includes('status="200"'))).toBe(true);
@@ -66,6 +67,12 @@ describe('httpMetrics', () => {
         expect(browse).toHaveLength(1);
         expect(browse[0].trim().endsWith('2')).toBe(true);
 
+        // Keep enough resolution to distinguish the long-tail stalls this
+        // metric is intended to expose rather than collapsing them into +Inf.
+        for (const upperBound of [15, 20, 30, 60]) {
+            expect(metrics).toContain(`le="${upperBound}"`);
+        }
+
         // The scrape of the metrics port must not be recorded. Asserted on the
         // total observation count rather than on the absence of a `/metrics`
         // label: `/metrics` is not a known route, so it would land in `other`

packages/web/src/promClient.ts

@@ -7,7 +7,7 @@ export const httpRequestDuration = new Histogram({
     name: 'http_request_duration_seconds',
     help: 'Duration of HTTP requests handled by the web server, in seconds',
     labelNames: ['method', 'route', 'status'],
-    buckets: [0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5, 10],
+    buckets: [0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5, 10, 15, 20, 30, 60],
 });
 registry.registerMetric(httpRequestDuration);