sthenos 0.1.1

A Python-scriptable load testing tool (Go binary wrapper)

Sthenos

Sthenos is a modern, high-performance load testing tool written in Go. It combines the raw power of Go with the simplicity of Python-like scripting (Starlark) for an effortless developer experience.

Features

• High Performance: Built on Go, using lightweight goroutines for Virtual Users (VUs).
• Python-like Scripting: Write test scripts in Starlark (a dialect of Python).
• CLI Driven: Simple, powerful command-line interface.
• Metrics: Detailed breakdown of HTTP request lifecycle (DNS, TLS, TTFB, etc.).
• Thresholds: Define pass/fail criteria directly in your script.
• Stages: Ramp up/down VUs to simulate real-world traffic patterns.
• Zero-Dependency Installation: pip install sthenos works instantly (bundles pre-compiled binaries).
• K6 Compatibility: Supports Stages, Checks, Thresholds, and Setup/Teardown lifecycles.
• Detailed Metrics: Breakdown of DNS, TLS, TTFB, and more.

Installation

Via PyPI (Recommended)

pip install sthenos

From Source

git clone https://github.com/richard24se/Sthenos.git
cd Sthenos/sthenos
go build -o sthenos main.go

Usage

Basic Run

./sthenos run script.py

Options

Override script defaults via CLI flags:

./sthenos run \
  --vus 10 \
  --duration 30s \
  --out json=results.json \
  --env HOST=api.staging.com \
  script.py

Flag	Description	Default
--vus	Number of Virtual Users	1
--duration	Test duration (e.g., 10s, 1m)	10s
--env	Set environment variable (KEY=VAL)	-
--out	Output format (currently json=path)	-
--graceful-stop	Timeout to wait for active VUs	30s
--verbose	Show detailed timing breakdown	false

Examples & Features

Sthenos scripting is designed to be intuitive. Below are examples covering all major features. Scripts are written in Starlark, which looks and feels like Python.

1. Basic Request (01_basic.py)

The simplest test—hitting an endpoint repeatedly.

# Command: sthenos run --vus 5 --duration 5s examples/01_basic.py
# 01_basic.py: Minimal load test

from sthenos import http, sleep

def default():
    # Perform a simple GET request
    http.get("http://localhost:9001/")
    sleep(0.2)
    sleep(1)

2. Traffic Stages (02_stages.py)

Simulate ramping up and down traffic patterns.

# Command: sthenos run examples/02_stages.py
# 02_stages.py: Ramping VUs using stages

from sthenos import http, sleep

# Define ramping stages
options = {
    "stages": [
        {"duration": "2s", "target": 5},   # Ramp up to 5 VUs
        {"duration": "5s", "target": 10},   # Stay at 5 VUs
        {"duration": "2s", "target": 0},   # Ramp down to 0
    ]
}

def default():
    http.get("http://localhost:9001/")
    sleep(0.5)

3. Fail/Pass Criteria (03_thresholds.py)

Ensure your system meets specific SLIs. The test exits with code 1 if thresholds fail.

# Command: sthenos run examples/03_thresholds.py
# 03_thresholds.py: Defining Pass/Fail criteria

from sthenos import http, check, sleep

options = {
    # Thresholds allow CI/CD integration
    "thresholds": {
        "http_req_duration": ["p(95) < 500"], # 95% of requests must be faster than 500ms
        "checks": ["rate > 0.95"],            # 95% of checks must pass
        "http_req_failed": ["rate < 0.01"],   # Less than 1% errors
    },
    "stages": [
        {"duration": "5s", "target": 100},
    ]
}

def default(ctx):
    res = http.get("http://localhost:9001/")
    
    # This check feeds the "checks" metric
    check(res, {
        "is status 200": lambda r: r.status == 200,
    })
    
    sleep(1)

4. Validating Responses (04_env_vars.py)

This example shows how to use environment variables.

# Command: sthenos run --env HOST=https://httpbin.org --env USER=admin examples/04_env_vars.py
# 04_env_vars.py: Using Environment Variables

from sthenos import http, check, sleep, ENV

def setup():
    # Access injected env vars via global ENV dict
    host = ENV.get("HOST", "http://localhost:9001")
    user = ENV.get("USER", "guest")
    print("[Setup] Target: {host}, User: {user}".format(host=host, user=user))
    return {"host": host}

def default(ctx):
    url = "{host}/".format(host=ctx["host"])
    http.get(url)
    sleep(1)

5. POST JSON Data (05_post_json.py)

Send JSON payloads easily.

# Command: sthenos run --vus 2 --duration 5s examples/05_post_json.py
# 05_post_json.py: Sending POST requests

from sthenos import http, check, sleep

def default(ctx):
    # TODO: Current MVP implementation supports basic POST
    # Future: support full JSON body as dict
    payload = '{"foo": "bar"}'
    
    res = http.post("http://localhost:9001/post", payload)
    
    check(res, {
        "status is 200": lambda r: r.status == 200,
    })
    
    sleep(0.1)

6. Environment Variables (06_checks.py)

This example shows how to use checks to validate responses.

# Command: sthenos run --vus 5 --duration 5s examples/06_checks.py
# 06_checks.py: Validating responses

from sthenos import http, check, sleep

def default(ctx):
    res = http.get("http://localhost:9001/get")
    
    # Checks don't stop execution but are recorded
    success = check(res, {
        "status is 200": lambda r: r.status == 200,
        "body size > 0": lambda r: len(r.body) > 0,
    })
    
    if not success:
        print("Request failed validation!")
    
    sleep(1)

7. Full Lifecycle (07_lifecycle.py)

Use setup() (once globally) to prepare data, and teardown() (once globally) to clean up.

# Command: sthenos run examples/07_lifecycle.py
# 07_lifecycle.py: Demonstrating the full test lifecycle
# Init -> Setup(once) -> VU(many) -> Teardown(once)

from sthenos import http, check, sleep

# 1. INIT PHASE
# Executed once per VU process/thread
print("[Phase] Init")


# 2. SETUP PHASE
# Executed once globally. Returns 'ctx' data.
def setup():
    print("[Phase] Setup: Generating Test Data...")
    return {"token": "secret_abc_123", "items": [1, 2, 3]}


# 3. VU PHASE
# Executed repeatedly. Receives 'ctx'.
def default(ctx):
    # print("[Phase] VU: Using token {}".format(token)) # Uncomment to see per-VU logs

    # Simulate work
    res = http.get("http://localhost:9001/headers", {"headers": {"Authorization": ctx["token"]}})

    # Validate that server received the token via Response Headers
    check(
        res,
        {
            "status is 200": lambda r: r.status == 200,
        },
    )
    check(
        res,
        {
            "token verified": lambda r: r.headers.get("X-Token-Received") == ctx["token"],
        },
    )

    sleep(0.5)


# 4. TEARDOWN PHASE
# Executed once globally. Receives 'ctx'.
def teardown(ctx):
    print("[Phase] Teardown: Data {} clean up complete.".format(ctx["items"]))

8. Complete Scenario (08_ecommerce.py)

Combine everything to simulate a real user journey.

# Command: sthenos run examples/08_ecommerce.py
# 08_ecommerce.py: User Journey Simulation
# Features: Stages, Thresholds, Env Vars, Setup, Checks, Sleep, POST

from sthenos import http, check, sleep, ENV  

# 1. Option Configuration
options = {
    # Ramping Load Pattern
    "stages": [
        {"duration": "10s", "target": 50},   # Ramp up to 5 users
        {"duration": "5s", "target": 5},   # Stay at 5 users
        {"duration": "2s", "target": 0},   # Ramp down to 0
    ],
    # Pass/Fail Criteria
    "thresholds": {
        "http_req_duration": ["p(95)<500"], # 95% of requests must be faster than 500ms
        "checks": ["rate>0.95"],            # 95% of checks must pass
        "http_req_failed": ["rate<0.01"],   # Less than 1% failure
    },
}

# 2. Setup Phase
def setup():
    # Use Environment Variable for dynamic targeting
    # usage: sthenos run --env HOST=https://my-api.com examples/08_ecommerce.py
    # usage: sthenos run --env HOST=https://my-api.com examples/08_ecommerce.py
    host = ENV.get("HOST", "http://localhost:9001")
    print("Setup: Targeting {}".format(host))
    return {"host": host}

# 3. VU Logic
def default(ctx):
    host = ctx["host"]
    
    # Step 1: Browse Home Page
    res = http.get("{}/get?page=home".format(host))
    check(res, {
        "home status 200": lambda r: r.status == 200,
    })
    sleep(1.0) # User thinks
    
    # Step 2: View Product
    res = http.get("{}/get?product=123".format(host))
    check(res, {
        "product status 200": lambda r: r.status == 200,
    })
    sleep(0.5)
    
    # Step 3: Add to Cart (POST)
    # Note: Sthenos supports string body for POST
    payload = '{"product_id": 123, "qty": 1}'
    params = {
        "headers": {
            "Content-Type": "application/json",
            "Authorization": "Bearer secret_token",
        }
    }
    res = http.post("{}/post".format(host), payload, params)
    
    check(res, {
        "cart add status 200": lambda r: r.status == 200,
    })
    
    sleep(1.0)

def teardown(data):
    print("Teardown: Test Complete.")

Metrics Output

Sthenos produces a k6-inspired summary to the console:

   _____ _______ _    _ ______ _   _  ____   _____
  / ____|__   __| |  | |  ____| \ | |/ __ \ / ____|
 | (___    | |  | |__| | |__  |  \| | |  | | (___
  \___ \   | |  |  __  |  __| | .   | |  | |\___ \
  ____) |  | |  | |  | | |____| |\  | |__| |____) |
 |_____/   |_|  |_|  |_|______|_| \_|\____/|_____/

Initial VUs: 100, Duration: 5s
Running Setup...
Setup: Targeting http://localhost:9001
Mode: Forced Constant (CLI Overrides). VUs: 100, Duration: 5s
Starting Constant Load: 100 VUs for 5s
running [=========================] 5s / 5s

Stopping VUs and waiting for graceful exit...
Running Teardown...
Teardown: Test Complete.

✓ checks...........................:   100.00% ✓     600 / 600
data_received......................:   118.4 kB      23.2 kB/s
data_sent..........................:   49.4 kB       9.7 kB/s
http_req_duration..................:   avg=10.67ms   min=0.00ms   med=1.06ms   max=85.21ms   p(90)=44.67ms   p(95)=65.27ms
http_reqs..........................:   600           117.47/s
http_req_failed....................:   0             0.00%
vus................................:   100           min=100   max=100
vus_max............................:   100           min=100   max=100


--- Thresholds ---
http_req_duration   p(95)<500   ... PASS
checks              rate>0.95   ... PASS
http_req_failed     rate<0.01   ... PASS
------------------

Comparisons

Feature	k6 (OSS)	Sthenos
Language	Go	Go
Scripting	JavaScript (ES6)	Starlark (Python dialect)
Engine	goja	go.starlark.net
Concurrency	Goroutines	Goroutines
Ecosystem	Mature	Experimental

License

STHENOS LICENSE