Failed when trying to create, get data from the database (pymongo, mongodb, docker-compose)

Question

I'm having the following error when I try to execute a get or post in my flask app.

mongo:27017: [Errno -2] Name does not resolve (configured timeouts: socketTimeoutMS: 20000.0ms, connectTimeoutMS: 20000.0ms), Timeout: 30s, Topology Description: <TopologyDescription id: 657c619ae1e4696f65e708c2, topology_type: Unknown, servers: [<ServerDescription ('mongo', 27017) server_type: Unknown, rtt: None, error=AutoReconnect('mongo:27017: [Errno -2] Name does not resolve (configured timeouts: socketTimeoutMS: 20000.0ms, connectTimeoutMS: 20000.0ms)')>]>

my app.py

from flask import Flask, jsonify
from pymongo import MongoClient
from loguru import logger
from bson.json_util import dumps

app = Flask(__name__)

MONGO_URI = "mongodb://admin:admin@mongo:27017/"

@app.route('/', methods=['GET'])
def get_data():
    try:
        logger.info('Connecting to MongoDB')
        client = MongoClient(MONGO_URI)
        logger.info('Connected to MongoDB')
        db = client.test
        collection = db.test
        data = collection.find({})
        serialized_data = dumps(data)
        logger.info('Data retrieved successfully')
        return jsonify({"data": serialized_data}), 200
    except Exception as e:
        return jsonify({"error": f"{str(e)}"}), 500

@app.route('/', methods=['POST'])
def create_data():
    try:
        logger.info('Connecting to MongoDB')
        client = MongoClient(MONGO_URI)
        logger.info('Connected to MongoDB')
        db = client.test
        collection = db.test
        data = collection.insert_one({"name": "test"})
        logger.info('Data created successfully')
        return jsonify({"data": data}), 200
    except Exception as e:
        return jsonify({"error": f"{str(e)}"}), 500

if __name__ == '__main__':
    app.run(host='0.0.0.0')

docker-compose

version: '3.9'

services:
  web:
    build:
      context: .
      dockerfile: Dockerfile
    ports:
      - "5000:5000"
    depends_on:
      - mongodb
      - nginx

  nginx:
    image: nginx:latest
    ports:
      - "80:80"
    volumes:
      - ./nginx.conf:/etc/nginx/nginx.conf:ro

  mongodb:
    image: mongo:latest
    ports:
      - "27017:27017"
    environment:
      - MONGO_INITDB_DATABASE=test
      - MONGO_INITDB_ROOT_USERNAME=admin
      - MONGO_INITDB_ROOT_PASSWORD=admin
      - MONGO_URI=mongodb://admin:admin@mongodb:27017/test
    volumes:
      - mongodb_data:/data/db

volumes:
  mongodb_data:

The error saying that there is a connection error doesn't make much sense to me, because the logs that are being made show that the request passes through the connection line.

Does anyone know how to solve it?

Answer 1

Docker containers are referenced by their service name; change your connection string to:

MONGO_URI = "mongodb://admin:admin@mongodb:27017/"

Note that creating the MongoClient object doesn't actually attempt a database connection, so you can't assume you're connected just because it doesn't fail at that point.