Load Testing Plan

Load Testing Plan Skill

Produce a complete load and performance testing plan for a service — covering test objectives, scenario definitions, tooling configuration, success thresholds, and CI integration. A good load testing plan eliminates ambiguity about what "performance is acceptable" means, so engineers can run tests and get a pass/fail answer without having to interpret raw numbers themselves.

Required Inputs

Ask for these if not already provided:

• Service name and key endpoints — which endpoints are under test (path, method, typical request/response shape)
• Current traffic baseline — current requests/sec, p50/p99 latency, error rate under normal load
• Peak traffic expectations — expected peak RPS (e.g. 10× baseline for flash sales, or seasonality peak)
• SLO targets — latency SLOs (p99 < X ms), error rate SLO (< Y%), availability target
• Preferred testing tool — k6, Locust, JMeter, Gatling, or no preference
• Test environment availability — dedicated load test environment, staging, or production (with traffic shaping)

Output Format

Load Testing Plan: [Service Name]

Author: [Name] | Team: [Team name] Date: [Date] | Review cycle: Before each major release and quarterly Testing tool: [k6 / Locust / JMeter / Gatling] Test environment: [Environment name and URL]

1. Objectives and Scope

What we are testing: [Service name] handles [describe function — e.g. "user authentication requests from the mobile and web clients"]. This plan validates that the service meets its SLOs under expected and elevated traffic conditions.

In scope:

• [Endpoint 1: METHOD /path — description]
• [Endpoint 2: METHOD /path — description]
• [Endpoint 3: METHOD /path — description]

Out of scope:

• [Any endpoints explicitly excluded and why — e.g. "admin APIs — low traffic, excluded from load test"]
• [Third-party integrations that cannot be load-tested — mock them instead]

2. Performance Targets (Success Criteria)

Every scenario has explicit pass/fail thresholds. A test run FAILS if any threshold is breached.

SLO reference: These thresholds are derived from the service SLOs — p99 < [Z ms], error rate < [0.1]%, availability [99.9]%.

3. Traffic Model

Baseline traffic (current production):

• Average RPS: [N] req/sec
• Peak RPS (observed): [N] req/sec
• Request distribution by endpoint:
  • [Endpoint 1]: [X]% of traffic
  • [Endpoint 2]: [Y]% of traffic
  • [Endpoint 3]: [Z]% of traffic

Simulated user behaviour:

• Think time between requests: [X–Y] seconds (randomised)
• Session duration: [N] minutes average
• Authenticated vs anonymous ratio: [X]%/[Y]%
• Geographic distribution: [Region 1 X]%, [Region 2 Y]%

4. Test Scenarios

Scenario 1: Baseline (Steady-State)

Purpose: Confirm the service performs acceptably under normal production load. Duration: 10 minutes Load profile: Ramp to [N] RPS over 2 minutes, hold for 8 minutes. Concurrency: [N] virtual users

Pass criteria: All thresholds in the Baseline column of the targets table above.

Scenario 2: Stress Test

Purpose: Find the breaking point — how much load can the service handle before SLOs are breached? Duration: 20–30 minutes Load profile: Ramp from [N] RPS (baseline) to [N × 5] RPS in 5-minute steps. Hold each step for 5 minutes. Stop at first SLO breach. Concurrency: Scales with RPS target

What to record:

• RPS at which p99 latency first exceeds SLO
• RPS at which error rate first exceeds SLO
• Whether the service recovers when load drops back to baseline

Scenario 3: Spike Test

Purpose: Simulate a sudden traffic surge (flash sale, viral event, bot attack). Duration: 15 minutes Load profile: Hold at [N] RPS (baseline) for 3 minutes, spike to [N × 10] RPS instantly, hold for 5 minutes, drop back to baseline for 7 minutes.

What to record:

• Latency during spike and recovery
• Whether the service sheds load gracefully (rate limiting, queue depth)
• Time to recover to baseline latency after spike ends

Scenario 4: Soak / Endurance Test

Purpose: Detect memory leaks, connection pool exhaustion, and slow degradation over time. Duration: 4–8 hours (run overnight) Load profile: Steady [N × 1.5] RPS (50% above baseline) for entire duration.

What to watch:

• Memory usage trend over time (should not grow unboundedly)
• Error rate trend (should be flat, not creeping up)
• GC pause frequency (JVM/Go services)
• Database connection pool utilisation
• p99 latency trend (should not creep up over hours)

5. Test Environment Requirements

Infrastructure

Data Seeding

Before every test run, ensure the environment has:

# Seed test users (needed for authenticated endpoint tests)
[seed command or script path — e.g. python scripts/seed_load_test_users.py --count 10000]

# Seed test data for read endpoints
[seed command — e.g. ./scripts/seed_products.sh --count 50000]

# Verify seed completed
[verification command — e.g. psql $DB_URL -c "SELECT COUNT(*) FROM users WHERE load_test=true"]

Test data rules:

• Never use real production user data in load tests
• Tag all test-generated records with load_test=true for easy cleanup
• Run cleanup after each test: [cleanup command]

6. Tooling Setup

k6 Script Skeleton

import http from 'k6/http';
import { check, sleep } from 'k6';
import { Rate, Trend } from 'k6/metrics';

// Custom metrics
const errorRate = new Rate('error_rate');
const endpointLatency = new Trend('endpoint_latency', true);

// Test configuration — override per scenario
export const options = {
  scenarios: {
    baseline: {
      executor: 'ramping-vus',
      startVUs: 0,
      stages: [
        { duration: '2m', target: [BASELINE_VUS] },
        { duration: '8m', target: [BASELINE_VUS] },
        { duration: '1m', target: 0 },
      ],
    },
  },
  thresholds: {
    http_req_duration: [
      'p(95)<[Y_MS]',
      'p(99)<[Z_MS]',
    ],
    error_rate: ['rate<0.01'],
    http_req_failed: ['rate<0.01'],
  },
};

// Auth helper — get token once per VU
export function setup() {
  const loginRes = http.post('[BASE_URL]/auth/login', JSON.stringify({
    username: `load_test_user_${Math.floor(Math.random() * 10000)}@example.com`,
    password: __ENV.LOAD_TEST_PASSWORD,
  }), { headers: { 'Content-Type': 'application/json' } });

  check(loginRes, { 'login ok': (r) => r.status === 200 });
  return { token: loginRes.json('access_token') };
}

export default function (data) {
  const headers = {
    Authorization: `Bearer ${data.token}`,
    'Content-Type': 'application/json',
  };

  // Endpoint 1: [Description]
  const res1 = http.get('[BASE_URL]/[endpoint-1]', { headers });
  check(res1, {
    '[endpoint-1] status 200': (r) => r.status === 200,
    '[endpoint-1] latency < [X]ms': (r) => r.timings.duration < [X],
  });
  errorRate.add(res1.status >= 400);
  endpointLatency.add(res1.timings.duration, { endpoint: '[endpoint-1]' });

  sleep(Math.random() * [THINK_TIME_MAX] + [THINK_TIME_MIN]);

  // Endpoint 2: [Description]
  const res2 = http.post('[BASE_URL]/[endpoint-2]',
    JSON.stringify({ [key]: '[value]' }),
    { headers }
  );
  check(res2, {
    '[endpoint-2] status 201': (r) => r.status === 201,
  });
  errorRate.add(res2.status >= 400);
}

Locust Script Skeleton (alternative)

from locust import HttpUser, task, between
import random

class [ServiceName]User(HttpUser):
    wait_time = between([THINK_TIME_MIN], [THINK_TIME_MAX])
    token = None

    def on_start(self):
        """Called once per simulated user — authenticate."""
        user_id = random.randint(1, 10000)
        response = self.client.post("/auth/login", json={
            "username": f"load_test_user_{user_id}@example.com",
            "password": "[LOAD_TEST_PASSWORD]",
        })
        self.token = response.json()["access_token"]
        self.headers = {"Authorization": f"Bearer {self.token}"}

    @task([WEIGHT_1])  # Weight = relative frequency
    def [endpoint_1_task](self):
        """[Endpoint 1 description]"""
        with self.client.get(
            "/[endpoint-1]",
            headers=self.headers,
            catch_response=True
        ) as response:
            if response.elapsed.total_seconds() > [LATENCY_THRESHOLD]:
                response.failure(f"Too slow: {response.elapsed.total_seconds()}s")

    @task([WEIGHT_2])
    def [endpoint_2_task](self):
        """[Endpoint 2 description]"""
        self.client.post(
            "/[endpoint-2]",
            json={"[key]": "[value]"},
            headers=self.headers,
        )

Running Tests

# k6 — run baseline scenario
k6 run --env BASE_URL=https://[test-env-url] scripts/load_test.js

# k6 — run stress scenario with output to InfluxDB
k6 run --out influxdb=http://[influxdb-host]:8086/k6 \
  --env SCENARIO=stress \
  scripts/load_test.js

# Locust — headless run
locust -f locustfile.py \
  --headless \
  --users [N] \
  --spawn-rate [N] \
  --run-time 10m \
  --host https://[test-env-url] \
  --csv=results/[run-id]

# Locust — web UI (interactive)
locust -f locustfile.py --host https://[test-env-url]