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Flask with SQLite

This guide explains how to create and deploy a Python Flask app using SQLite. To run this example, follow these steps:

  1. Install the kraft CLI tool and a container runtime engine, for example Docker.

  2. Clone the examples repository and cd into the examples/python3.12-flask3.0-sqlite/ directory:

Code(bash)
 
git clone https://github.com/kraftcloud/examples
cd examples/python3.12-flask3.0-sqlite/

Make sure to log into Unikraft Cloud by setting your token and a metro close to you. This guide uses fra (Frankfurt, 🇩🇪):

Code(bash)
 
# Set Unikraft Cloud access token
export UKC_TOKEN=token
# Set metro to Frankfurt, DE
export UKC_METRO=fra

When done, invoke the following command to deploy this app on Unikraft Cloud:

Code(bash)
 
kraft cloud deploy -p 443:8080 -M 512 .
Code(ansi)
 
[●] Deployed successfully!
 │
 ├────────── name: python312-flask30-sqlite-qodkd
 ├────────── uuid: e00e7aca-962d-409c-87c2-c245ca08b54b
 ├───────── state: running
 ├─────────── url: https://lingering-orangutan-840mmdvd.fra.unikraft.app
 ├───────── image: python312-flask30-sqlite@sha256:bdb0bf35a9675b9b3836cbb626606da0606334d91768c7ba31195c3062d6f517
 ├───── boot time: 166.25 ms
 ├──────── memory: 512 MiB
 ├─────── service: lingering-orangutan-840mmdvd
 ├── private fqdn: python312-flask30-sqlite-qodkd.internal
 ├──── private ip: 172.16.3.3
 └────────── args: /usr/bin/python3 /app/server.py

In this case, the instance name is python312-flask30-sqlite-qodkd and the address is https://lingering-orangutan-840mmdvd.fra.unikraft.app. They're different for each run.

Use curl to query the Unikraft Cloud instance of the Python-based HTTP web server:

Code(bash)
 
curl https://young-night-5fpf0jj8.fra.unikraft.app
Code(text)
 
<!doctype html>
<html lang="en">
    [...]
    <h1> Welcome to FlaskBlog </h1>

        <a href="/1">
            <h2>First Post</h2>
        </a>
        <span class="badge badge-primary">2024-02-15 22:01:07</span>
        <a href="/1/edit">
            <span class="badge badge-warning">Edit</span>
        </a>
        <hr>

        <a href="/2">
            <h2>Second Post</h2>
        </a>
</html>

You can list information about the instance by running:

Code(bash)
 
kraft cloud instance list
Code(text)
 
NAME                            FQDN                                           STATE    CREATED AT   IMAGE                               MEMORY   ARGS                             BOOT TIME
python312-flask30-sqlite-qodkd  lingering-orangutan-840mmdvd.fra.unikraft.app  running  1 minute ago  python312-flask30-sqlite@sha256...  512 MiB  /usr/bin/python3 /app/server.py  166250us

When done, you can remove the instance:

Code(bash)
 
kraft cloud instance remove python312-flask30-sqlite-qodkd

Implementation details

The app uses the following files:

  • schema.sql: SQL schema for the database
  • init_db.py: script to initialized the database file from schema.sql in /app/database.db
  • server.py + templates/: the actual Flask-based implementation: Python source code file and HTML template files
  • requirements.txt: pip configuration file to install required packages: Flask and SQLite
  • Kraftfile: the Unikraft Cloud specification
  • Dockerfile: the Docker-specified app filesystem

Lines in the Kraftfile have the following roles:

  • spec: v0.6: The current Kraftfile specification version is 0.6.

  • runtime: python:3.12: The Unikraft runtime kernel to use is Python 3.12.

  • rootfs: ./Dockerfile: Build the app root filesystem using the Dockerfile.

  • cmd: ["/usr/bin/python3", "/app/server.py"]: Use /usr/bin/python3 /app/server.py as the starting command of the instance.

Lines in the Dockerfile have the following roles:

  • FROM scratch: Build the filesystem from the scratch container image, to create a base image.

  • COPY rules copy required files. The process copies the requirements.txt file before running pip3 install. The process copies other files (including schema.sql, init_db.py) for the initialization of the database.

  • RUN commands trigger actions such as installing Python packages and initializing the database.

  • The new scratch image contains the relevant contents required by the app:

    • the SQLite dynamic library: /usr/lib/x86_64-linux-gnu/libsqlite3.so.0
    • the Python package files: /usr/local/lib/python3.12
    • the /app directory

Customize your app

To customize the app, update app files in the repository:

  • schema.sql: Update the database schema.
  • server.py, templates/: Update the Flask app..
  • requirements.txt, Dockerfile: Update the list of Python packages used by the app.
  • Kraftfile: Update the command line used to start the app.

The following options are available for customizing the app:

  • If you only update the implementation in the server.py source file or template/ directory, and the database schema in schema.sql, you don't need to make any other changes.

  • If you create any new source files, copy them into the app filesystem by using the COPY command in the Dockerfile.

  • If you add new dependencies in requirements.txt, the RUN pip3 install in the Dockerfile command should take care of everything. It may be the case that you need to copy other files, such as the /usr/lib/x86_64-linux-gnu/libsqlite3.so.0 for SQLite, via COPY commands in the Dockerfile. More extensive changes may require extending the Dockerfile (see Dockerfile syntax reference).

  • If you add a new Python source file that's running the main() function, update the cmd line in the Kraftfile and replace server.py to run that file when creating the instance.

Learn more

Use the --help option for detailed information on using Unikraft Cloud:

Code(bash)
 
kraft cloud --help

Or visit the CLI Reference.

Last modified on
FerretDBFlask