setup project

.vscode/launch.json

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+{
+    "version": "0.2.0",
+    "configurations": [
+        {
+            // Use IntelliSense to find out which attributes exist for C# debugging
+            // Use hover for the description of the existing attributes
+            // For further information visit https://github.com/dotnet/vscode-csharp/blob/main/debugger-launchjson.md.
+            "name": ".NET Core Launch (web)",
+            "type": "coreclr",
+            "request": "launch",
+            "preLaunchTask": "build",
+            // If you have changed target frameworks, make sure to update the program path.
+            "program": "${workspaceFolder}/API.Stories/bin/Debug/net9.0/API.Stories.dll",
+            "args": [],
+            "cwd": "${workspaceFolder}/API.Stories",
+            "stopAtEntry": false,
+            // Enable launching a web browser when ASP.NET Core starts. For more information: https://aka.ms/VSCode-CS-LaunchJson-WebBrowser
+            "serverReadyAction": {
+                "action": "openExternally",
+                "pattern": "\\bNow listening on:\\s+(https?://\\S+)"
+            },
+            "env": {
+                "ASPNETCORE_ENVIRONMENT": "Development"
+            },
+            "sourceFileMap": {
+                "/Views": "${workspaceFolder}/Views"
+            }
+        },
+        {
+            "name": ".NET Core Attach",
+            "type": "coreclr",
+            "request": "attach"
+        }
+    ]
+}

.vscode/tasks.json

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+{
+    "version": "2.0.0",
+    "tasks": [
+        {
+            "label": "build",
+            "command": "dotnet",
+            "type": "process",
+            "args": [
+                "build",
+                "${workspaceFolder}/API.Stories/API.Stories.csproj",
+                "/property:GenerateFullPaths=true",
+                "/consoleloggerparameters:NoSummary;ForceNoAlign"
+            ],
+            "problemMatcher": "$msCompile"
+        },
+        {
+            "label": "publish",
+            "command": "dotnet",
+            "type": "process",
+            "args": [
+                "publish",
+                "${workspaceFolder}/API.Stories/API.Stories.csproj",
+                "/property:GenerateFullPaths=true",
+                "/consoleloggerparameters:NoSummary;ForceNoAlign"
+            ],
+            "problemMatcher": "$msCompile"
+        },
+        {
+            "label": "watch",
+            "command": "dotnet",
+            "type": "process",
+            "args": [
+                "watch",
+                "run",
+                "--project",
+                "${workspaceFolder}/API.Stories/API.Stories.csproj"
+            ],
+            "problemMatcher": "$msCompile"
+        }
+    ]
+}

API.Stories.LoadTests/.gitignore

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+node_modules/
+reports/*.json
+reports/*.html

API.Stories.LoadTests/artillery/processor.cjs

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+'use strict';
+
+const defaultTopkValues = [1, 5, 10, 20, 30, 50];
+const topkValues = parseTopkValues(process.env.TOPK_VALUES);
+
+function parseTopkValues(raw) {
+  if (!raw || typeof raw !== 'string') {
+    return defaultTopkValues;
+  }
+
+  const parsed = raw
+    .split(',')
+    .map((x) => Number.parseInt(x.trim(), 10))
+    .filter((x) => Number.isInteger(x) && x > 0);
+
+  return parsed.length > 0 ? parsed : defaultTopkValues;
+}
+
+function pickTopK(context, events, done) {
+  const idx = Math.floor(Math.random() * topkValues.length);
+  context.vars.topk = topkValues[idx];
+  done();
+}
+
+function validateTopKResponse(requestParams, response, context, events, done) {
+  if (response.statusCode !== 200) {
+    return done(new Error(`Expected status 200, got ${response.statusCode}`));
+  }
+
+  let body;
+  try {
+    body = typeof response.body === 'string' ? JSON.parse(response.body) : response.body;
+  } catch (err) {
+    return done(new Error(`Response is not valid JSON: ${err.message}`));
+  }
+
+  if (!Array.isArray(body)) {
+    return done(new Error('Response body should be a JSON array of stories'));
+  }
+
+  const expectedTopK = Number.parseInt(context.vars.topk || '30', 10);
+
+  if (body.length > expectedTopK) {
+    return done(new Error(`Response returned ${body.length} items, expected at most ${expectedTopK}`));
+  }
+
+  for (let i = 0; i < body.length; i++) {
+    const item = body[i];
+
+    if (typeof item !== 'object' || item === null) {
+      return done(new Error(`Item at index ${i} is not an object`));
+    }
+
+    if (typeof item.id !== 'number' || typeof item.score !== 'number' || typeof item.title !== 'string') {
+      return done(new Error(`Item at index ${i} is missing required fields (id, score, title)`));
+    }
+
+    if (i > 0 && body[i - 1].score < item.score) {
+      return done(new Error('Response is not sorted by score in descending order'));
+    }
+  }
+
+  context.vars.storyCount = body.length;
+  done();
+}
+
+function recordStoryCount(requestParams, response, context, events, done) {
+  const count = Number.isInteger(context.vars.storyCount) ? context.vars.storyCount : 0;
+  events.emit('histogram', 'stories.returned_per_request', count);
+  events.emit('counter', 'stories.items_returned_total', count);
+  done();
+}
+
+module.exports = {
+  pickTopK,
+  validateTopKResponse,
+  recordStoryCount
+};

API.Stories.LoadTests/artillery/topk-load-test.yml

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+config:
+  target: "http://localhost:5038"
+  processor: "./processor.cjs"
+  plugins:
+    metrics-by-endpoint:
+      useOnlyRequestNames: true
+    ensure:
+      conditions:
+        - expression: "http.responses > 0"
+        - expression: "http.codes.200 / http.responses >= 0.95"
+        - expression: "http.response_time.p95 < 2000"
+        - expression: "http.response_time.p99 < 4000"
+  defaults:
+    headers:
+      Accept: "application/json"
+      x-api-version: "1.0"
+  environments:
+    smoke:
+      phases:
+        - duration: 20
+          arrivalRate: 1
+          name: "Smoke ramp"
+    baseline:
+      phases:
+        - duration: 30
+          arrivalRate: 2
+          rampTo: 8
+          name: "Warm-up"
+        - duration: 90
+          arrivalRate: 8
+          rampTo: 20
+          name: "Steady load"
+    spike:
+      phases:
+        - duration: 30
+          arrivalRate: 3
+          rampTo: 10
+          name: "Ramp-up"
+        - duration: 30
+          arrivalRate: 35
+          rampTo: 80
+          name: "Spike"
+        - duration: 30
+          arrivalRate: 10
+          name: "Cool-down"
+    soak:
+      phases:
+        - duration: 120
+          arrivalRate: 8
+          name: "Soak"
+
+scenarios:
+  - name: "TopK mixed profile"
+    weight: 80
+    flow:
+      - function: "pickTopK"
+      - get:
+          name: "GET /api/v1/topk/:topk"
+          url: "/api/v1/topk/{{ topk }}"
+          afterResponse:
+            - "validateTopKResponse"
+            - "recordStoryCount"
+      - think: 1
+
+  - name: "Hot path pressure (topk=30)"
+    weight: 20
+    flow:
+      - loop:
+          - get:
+              name: "GET /api/v1/topk/30"
+              url: "/api/v1/topk/30"
+              afterResponse:
+                - "validateTopKResponse"
+                - "recordStoryCount"
+          - think: 0.5
+        count: 3