python 27 lines · 6 steps

Building a health check endpoint in Flask

A /healthz route probes the database and reports overall service health with the right HTTP status code.

Explained by highlit
Flask Intermediate health-check blueprint error-handling http-status database
1from flask import Blueprint, jsonify
2from sqlalchemy import text
3from sqlalchemy.exc import SQLAlchemyError
4 
5from .extensions import db
6 
7health_bp = Blueprint("health", __name__)
8 
9 
10@health_bp.get("/healthz")
11def healthz():
12 checks = {"database": _check_database()}
13 healthy = all(component["ok"] for component in checks.values())
14 payload = {
15 "status": "ok" if healthy else "degraded",
16 "checks": checks,
17 }
18 return jsonify(payload), 200 if healthy else 503
19 
20 
21def _check_database():
22 try:
23 db.session.execute(text("SELECT 1"))
24 except SQLAlchemyError as exc:
25 db.session.rollback()
26 return {"ok": False, "error": str(exc.__cause__ or exc)}
27 return {"ok": True}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1A liveness endpoint should actually exercise dependencies, not just return a static 200.
  2. 2Return 503 when a component is degraded so load balancers and orchestrators can react correctly.
  3. 3Catch dependency exceptions and roll back so one failed probe doesn't poison the session.

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