Add FastAPI service, Dockerfile and compose

webapp/.dockerignore

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+.venv/
+__pycache__/
+*.pyc
+.pytest_cache/

webapp/.gitignore

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+.venv/
+__pycache__/
+*.pyc
+.pytest_cache/

webapp/Dockerfile

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+FROM python:3.12-slim
+
+ENV PYTHONDONTWRITEBYTECODE=1 PYTHONUNBUFFERED=1
+WORKDIR /app
+
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+
+COPY app ./app
+
+RUN useradd --system --uid 1001 appuser
+USER appuser
+
+EXPOSE 8000
+HEALTHCHECK --interval=15s --timeout=3s --retries=3 \
+  CMD python -c "import urllib.request; urllib.request.urlopen('http://localhost:8000/health')" || exit 1
+
+CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000"]

webapp/app/main.py

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+import time
+
+from fastapi import FastAPI, HTTPException, Request, Response
+from prometheus_client import CONTENT_TYPE_LATEST, Counter, Histogram, generate_latest
+
+app = FastAPI(title="DevOps Test Service")
+
+REQUESTS = Counter(
+    "http_requests_total", "Total HTTP requests", ["method", "path", "status"]
+)
+LATENCY = Histogram(
+    "http_request_duration_seconds", "Request latency in seconds", ["path"]
+)
+
+
+@app.middleware("http")
+async def track_metrics(request: Request, call_next):
+    start = time.perf_counter()
+    response = await call_next(request)
+    path = request.url.path
+    REQUESTS.labels(request.method, path, response.status_code).inc()
+    LATENCY.labels(path).observe(time.perf_counter() - start)
+    return response
+
+
+@app.get("/")
+def index():
+    return {"message": "Hello from the DevOps test service"}
+
+
+@app.get("/health")
+def health():
+    return {"status": "ok"}
+
+
+@app.get("/error")
+def error():
+    # Used to generate 5xx responses and trigger the high-error-rate alert
+    raise HTTPException(status_code=500, detail="simulated failure")
+
+
+@app.get("/metrics")
+def metrics():
+    return Response(generate_latest(), media_type=CONTENT_TYPE_LATEST)

webapp/compose.yml

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+services:
+  webapp:
+    build: .
+    image: webapp:latest
+    container_name: webapp
+    restart: unless-stopped
+    ports:
+      - "8000:8000"
+    networks:
+      - monitoring-net
+
+networks:
+  monitoring-net:
+    external: true

webapp/pytest.ini

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+[pytest]
+pythonpath = .

webapp/requirements-dev.txt

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+-r requirements.txt
+pytest
+httpx

webapp/requirements.txt

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+fastapi
+uvicorn[standard]
+prometheus-client

webapp/tests/test_app.py

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+from fastapi.testclient import TestClient
+
+from app.main import app
+
+client = TestClient(app)
+
+
+def test_index():
+    r = client.get("/")
+    assert r.status_code == 200
+
+
+def test_health():
+    r = client.get("/health")
+    assert r.status_code == 200
+    assert r.json() == {"status": "ok"}
+
+
+def test_error_endpoint_returns_500():
+    assert client.get("/error").status_code == 500
+
+
+def test_metrics_exposed():
+    client.get("/health")
+    r = client.get("/metrics")
+    assert r.status_code == 200
+    assert "http_requests_total" in r.text