Docker Basics Lab — Flask + SQLAlchemy + Postgres

Minimal Flask API containerized with Docker. Provisioned with Docker Compose alongside Postgres on a private network with a named volume. Includes structured JSON logs, a liveness endpoint, and a simple notes table to demonstrate persistence. Supports horizontal scaling.

Tech & Tools

• Python 3.11
• Flask 3.0, SQLAlchemy 2.0, (psycopg2-binary 2.9.x or psycopg 3.x)
• Gunicorn (1 worker for demo)
• Docker Desktop (Linux engine) + Docker Compose v2
• Postgres 16

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Repo Structure

docker-lab-flask-sqlalchemy/ ├─ app.py ├─ requirements.txt ├─ Dockerfile ├─ docker-compose.yml ├─ .dockerignore └─ README.md

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Quick Start

Windows PowerShell-friendly commands shown. If :8000 is busy, change host mapping to 8001:8000 in compose.

# 0) From repo root
docker compose up -d --build
docker compose ps

# 1) Liveness
Invoke-WebRequest http://localhost:8000/alive | Select-Object -Expand Content
# expected: {"status":"ok"}

# 2) Logs (structured JSON)
docker compose logs -f web
Endpoints

GET /alive – liveness check → {"status":"ok"}

GET /identity – shows the container hostname (for scale demo) → {"host":"api-1"...}

POST /notes – create a note
Body: {"body":"hello flask"}

GET /notes – list notes → {"notes":[{"id":1,"body":"..."}]}

# Create a note
Invoke-RestMethod -Method Post -Uri http://localhost:8000/notes `
  -Body (@{body="hello flask"} | ConvertTo-Json) `
  -ContentType "application/json"

# List notes
Invoke-WebRequest http://localhost:8000/notes | Select-Object -Expand Content

docker compose logs -f web

#Sample:

{"event":"http_access","method":"GET","path":"/alive","status":200,"duration_ms":3,"trace_id":null}
{"event":"whoami","host":"web-1"}

#Persistent Demo

# Create table + insert via SQL (also done automatically in app routes)
docker compose exec db psql -U app -d appdb -c "CREATE TABLE IF NOT EXISTS notes(id SERIAL PRIMARY KEY, body TEXT);"
docker compose exec db psql -U app -d appdb -c "INSERT INTO notes(body) VALUES ('persist-demo');"
docker compose exec db psql -U app -d appdb -c "SELECT * FROM notes;"

# Restart only DB, verify row persists
docker compose restart db
docker compose exec db psql -U app -d appdb -c "SELECT * FROM notes;"

#stack teardown but keep volume

docker compose down
docker compose up -d
docker compose exec db psql -U app -d appdb -c "SELECT * FROM notes;"