HTTP Load Profiler — Stepped Concurrency Load Test + Inflection Point Analysis
Run stepped concurrency load tests against HTTP services, automatically collect latency percentiles, and detect performance inflection points.
Features
- Dual engine support: Auto-detects wrk (preferred) or ab (Apache Bench); manual override available
- Stepped concurrency: Ramps up through user-defined concurrency levels (default: 1 → 10 → 50 → 100 → 200 → 500)
- Latency percentiles: Collects p50 / p90 / p99 latency at each level
- Inflection point detection: Automatically identifies four types of performance inflection points
- p99 latency accelerating (increase exceeds 2x the previous step's increase)
- Throughput efficiency dropping significantly (RPS per connection drops > 40%)
- Throughput saturated while latency spikes (RPS growth < 10%, p99 growth > 50%)
- Error rate surging (exceeds 1% and doubles from previous step)
- Optimal concurrency recommendation: Automatically suggests the best concurrency level based on inflection points
- Zero Python dependencies: Pure standard library implementation
Quick Start
bash# Basic usage — run default stepped load test against target URL python3 scripts/http_benchmark.py https://example.com/api/health # Custom concurrency steps and duration per step python3 scripts/http_benchmark.py https://example.com/api/health -s 5,20,50,100,300 -d 15 # Specify ab as the engine python3 scripts/http_benchmark.py https://example.com/ -t ab # JSON-only output (for programmatic parsing) python3 scripts/http_benchmark.py https://example.com/api/health --json # Use ab with a specific number of requests per step python3 scripts/http_benchmark.py https://example.com/ -t ab -n 5000 # Save JSON report to a file python3 scripts/http_benchmark.py https://example.com/api/health --json > report.json
Parameters
| Parameter | Short | Default | Description |
|---|---|---|---|
url | — | (required) | Target URL (http:// or https://) |
--steps | -s | 1,10,50,100,200,500 | Concurrency steps (comma-separated positive integers) |
--duration | -d | 10 | Duration per step in seconds (used directly by wrk; ab estimates request count from this) |
--requests | -n | concurrency×100 | Total requests per step when using ab |
--tool | -t | auto-detect | Specify load testing tool: wrk or ab |
--threads | — | min(concurrency, CPU cores) | Thread count for wrk |
--json | — | false | Output JSON only |
Output Format
Human-readable (default)
Tool: wrk Target URL: https://example.com/api/health Concurrency steps: [1, 10, 50, 100, 200, 500] Duration per step: 10s ---------------------------------------------------------------------------------- Conc. | RPS | Avg(ms) | P50(ms) | P90(ms) | P99(ms) | Errors | Inflection ---------------------------------------------------------------------------------- 1 | 245.3 | 4.1 | 3.8 | 5.2 | 8.1 | 0.00% | 10 | 2301.5 | 4.3 | 4.0 | 5.8 | 9.3 | 0.00% | 50 | 9876.2 | 5.1 | 4.6 | 7.2 | 12.5 | 0.00% | 100 | 14523.1 | 6.9 | 5.8 | 10.3 | 22.7 | 0.00% | 200 | 15102.3 | 13.2 | 10.1 | 22.5 | 58.3 | 0.12% | ◀ 500 | 14890.5 | 33.6 | 28.3 | 55.2 | 132.1 | 1.35% | ◀ ---------------------------------------------------------------------------------- Inflection point analysis: ▶ Concurrency 200: - p99 latency accelerating: 22.7ms → 58.3ms (increase 35.6ms, previous step increase 10.2ms) - Throughput saturated with latency spike: RPS grew only 3.9% while p99 latency grew 156.8% ▶ Concurrency 500: - Error rate surging: 0.12% → 1.35% Recommended optimal concurrency: 100
JSON format (--json)
json{ "url": "https://example.com/api/health", "tool": "wrk", "duration_per_step": 10, "steps": [ { "concurrency": 1, "rps": 245.3, "avg_latency_ms": 4.1, "p50_ms": 3.8, "p90_ms": 5.2, "p99_ms": 8.1, "total_requests": 2453, "errors": 0 } ], "inflection_points": [ { "concurrency": 200, "step_index": 4, "reasons": ["p99 latency accelerating: ..."] } ], "recommended_concurrency": 100 }
Prerequisites
At least one of wrk or ab must be installed:
bash# Ubuntu / Debian sudo apt-get install wrk # recommended sudo apt-get install apache2-utils # ab # macOS brew install wrk # ab is pre-installed on macOS
Inflection Point Detection Algorithm
For each concurrency level, the following metrics are compared against the two preceding levels:
- p99 latency acceleration: Triggers when the current p99 increase exceeds 2x the previous step's increase
- Throughput efficiency: Triggers when RPS per connection drops > 40% from the previous step
- Saturation detection: Triggers when RPS growth < 10% while p99 growth > 50%
- Error rate: Triggers when rate exceeds 1% and doubles from the previous step
Recommended optimal concurrency: The concurrency level one step before the first inflection point. If no inflection point is found, the level with the highest RPS is selected.
Important Notes
- Load testing generates real traffic against the target service — do not run against production services without authorization
- wrk provides more accurate latency percentiles than ab (wrk uses HdrHistogram)
- ab does not support a duration parameter; the script approximates timing via total request count
- A minimum of 10 seconds per step is recommended for stable results
