Plugging Apps Together

In this guide we will show you how to connect two apps together in Unikraft Cloud (UKC); we will use, as example, a web server written in Python as frontend and a MariaDB instance as backend, as shown in this diagram:

If you haven’t come across what a service is yet, you can have a glance at this guide, but essentially in UKC a service is the mechanism we use to expose apps to the Internet. So in this guide we will attach the web server instance to a service so that it’s externally accessible, and then connect that instance to the MariaDB instance via a private connection/IP.

Setting it Up

To start, let’s create the MariaDB instance (you can get more details about this in the MariaDB guide):

git clone https://github.com/unikraft-cloud/examples
cd examples/mariadb
kraft cloud deploy --name mariadb -M 1024 .

Note that we don’t specify the -p flag, since this instance will be private, i.e., it does not need to connect to the Internet and so no service is needed for it. We use the --name flag to tell UKC to set the instance’s name to mariadb, but more importantly, to use it as its private DNS name so we can put that into our web server later. The resulting output of the deploy command should be similar to:

[●] Deployed successfully!
 │
 ├────────── name: mariadb
 ├────────── uuid: 269019de-f7dc-4077-9568-012ad594ca87
 ├───────── state: running
 ├─────────── url: wispy-moon-dpg6d54i.fra0.kraft.host
 ├───────── image: mariadb@sha256:6abb4f2ba4501068a84885d7b8b127adaf3d83c25fd43e79d5a142f6d8703c93
 ├───── boot time: 162.65 ms
 ├──────── memory: 1024 MiB
 ├── private fqdn: mariadb.internal
 ├──── private ip: 172.16.6.5
 └────────── args: /usr/sbin/mariadbd --user=root --log-bin

Note the private fqdn field’s value of mariadb.internal which will go into our Python server code.

Next we need to create the Python server to connect to the DB. We’ll use Flask for this:

git clone https://github.com/unikraft-cloud/examples
cd examples/http-python3.12-flask3.0

Replace the contents of server.py and requirements.txt with:

server.py
requirements.txt

from flask import Flask, jsonify
import mysql.connector

app = Flask(__name__)

db_config = {
   'host': 'mariadb.internal',
   'user': 'root',
   'password': 'unikraft',
   'database': 'mysql',
   'charset': 'utf8mb4',
   'collation': 'utf8mb4_unicode_ci'
}

def get_data_from_database():
   try:
       connection = mysql.connector.connect(**db_config)
       cursor = connection.cursor()

       # Replace this query with your actual SQL query
       query = "SELECT count(*) FROM user;"
       cursor.execute(query)

       data = cursor.fetchall()

       return data

   except Exception as e:
       print(f"Error: {e}")
       return None

   finally:
       if connection.is_connected():
           cursor.close()
           connection.close()

@app.route('/')
def get_data():
   data = get_data_from_database()

   if data is not None:
       return jsonify({'data': data})
   else:
       return jsonify({'error': 'Failed to retrieve data from the database'})

if __name__ == '__main__':
   app.run(host='0.0.0.0', port=8080)

flask>=3.0,<3.1
mysql-connector-python

With this in place, let’s start our Flask web server and create a service for it via the -p flag:

kraft cloud deploy -M 512 -p 443:8080 .

You should see output similar to:

[●] Deployed successfully!
 │
 ├────────── name: http-python312-flask30-hb8p8
 ├────────── uuid: eea65094-33fe-423f-b820-0bdaa875a494
 ├───────── state: running
 ├─────────── url: https://quiet-river-w2muxbwe.fra0.kraft.host
 ├───────── image: http-python312-flask30@sha256:49bba8cbd207391c6a8b785b7b6eeb1ff2f959618aa7f80b30dc5c252996e120
 ├───── boot time: 267.91 ms
 ├──────── memory: 512 MiB
 ├─────── service: quiet-river-w2muxbwe
 ├── private fqdn: http-python312-flask30-hb8p8.internal
 ├──── private ip: 172.16.6.7
 └────────── args: /usr/bin/python3 /app/server.py

So now we have our Flask instance attached to a service named quiet-river-w2muxbwe and with public URL https://quiet-river-w2muxbwe.fra0.kraft.host.

Testing it

Simply curl the URL:

curl https://quiet-river-w2muxbwe.fra0.kraft.host

You should get results from the MariaDB database, e.g.,:

{"data":[[6]]}

This is the result from the SELECT count(*) FROM user; query.

Learn More

The kraft cloud CLI reference
Unikraft Cloud’s REST API reference
Many more guides here