Example apps

Flask with MongoDB

Flask is a lightweight WSGI web application framework in Python, and MongoDB is a NoSQL database that stores data in JSON-like documents. This example deploys three services on Unikraft Cloud: NGINX (reverse proxy), Flask (backend), and MongoDB (database).

Credits: This example is based on this Awesome Compose example.

Deployment

To run this example, follow these steps:

Install the unikraft CLI. You need a BuildKit builder. The easiest way to get one is via Docker. Alternatively, you can also directly set up and use BuildKit, see the quick start.

Clone the examples repository and cd into the examples/nginx-flask-mongo directory:

Code
git clone https://github.com/unikraft-cloud/examples
cd examples/nginx-flask-mongo/

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

Code
unikraft login

MongoDB

Create a volume for MongoDB data persistence:

Code
unikraft volume create --metro fra --name mongo-data --size 1G

You can list the created volume by running:

Code
unikraft volume list

Code
METRO  NAME        STATE      SIZE  CREATED
fra    mongo-data  available  1GiB  just now

First, deploy the MongoDB instance. MongoDB is an internal service (not publicly accessible), reached via the mongo.internal domain:

Code
unikraft build ./mongo --output <my-org>/mongo:latest
unikraft run --metro fra \
  -m 1024M \
  --scale-to-zero policy=idle,cooldown-time=1000,stateful=true \
  --domain mongo.internal \
  --volume mongo-data:/data/db \
  --image <my-org>/mongo:latest

The output shows the MongoDB instance details:

Code
metro:           fra
name:            mongo-o3qhq
uuid:            90158c53-6654-4e73-bad1-1d6ab4452001
state:           starting
image:           <my-org>/mongo
resources:
  memory:        1GiB
  vcpus:         1
service:
  name:          restless-glade-l8pu2mf0
  uuid:          77a04441-2479-433a-b468-32f23e475f58
  domains:
  - fqdn:        mongo.internal
volumes:
- name:          mongo-data
  uuid:          9c7723f3-7e1f-4e06-afe6-c811240faf5a
  at:            /data/db
networks:
- uuid:          4f891227-d381-42f4-88a4-25a97b95a9e3
  private-ip:    10.0.15.21
  mac:           12:b0:0a:00:0f:15
timestamps:
  created:       just now
scale-to-zero:
  enabled:       true
  policy:        idle
  stateful:      true
  cooldown-time: 1s

Flask

Next, deploy the Flask backend. It connects to MongoDB using the MONGO_SERVER_URL environment variable and is reached internally via backend.internal:

Code
unikraft build ./flask --output <my-org>/flask:latest
unikraft run --metro fra \
  -m 1024M \
  --scale-to-zero policy=on,cooldown-time=1000 \
  --domain backend.internal \
  --env FLASK_SERVER_PORT=9091 \
  --env MONGO_SERVER_URL=mongo.internal:27017 \
  --image <my-org>/flask:latest

The output shows the Flask instance details:

Code
metro:                 fra
name:                  flask-9a68z
uuid:                  bb6d91f7-0714-45e5-b14a-ec82a5dac36e
state:                 starting
image:                 <my-org>/flask
runtime:
  env:
    FLASK_SERVER_PORT: 9091
    MONGO_SERVER_URL:  mongo.internal:27017
resources:
  memory:              1GiB
  vcpus:               1
service:
  name:                broken-bird-8isa6q21
  uuid:                cd9fe757-784a-49d4-8936-1b6859b3a72d
  domains:
  - fqdn:              backend.internal
networks:
- uuid:                2da7f679-7067-4fb5-908b-853607d383f2
  private-ip:          10.0.17.97
  mac:                 12:b0:0a:00:11:61
timestamps:
  created:             just now
scale-to-zero:
  enabled:             true
  policy:              on
  cooldown-time:       1s

NGINX

Finally, deploy NGINX as the public-facing reverse proxy. It forwards requests to the Flask backend at backend.internal:9091 by default. To use a different backend domain, set the BACKEND_HOST environment variable to the same value you pass as the Flask domain.

Code
unikraft build ./nginx --output <my-org>/nginx:latest
unikraft run --metro fra \
  -m 512M \
  -p 443:80/tls+http \
  --scale-to-zero policy=on,cooldown-time=1000 \
  -e BACKEND_HOST=backend.internal \
  --image <my-org>/nginx:latest

The output shows the NGINX instance details including its public FQDN:

Code
metro:           fra
name:            nginx-jnpwi
uuid:            57f64e99-bd06-46fd-98f4-26b64751623e
state:           starting
image:           <my-org>/nginx
resources:
  memory:        512MiB
  vcpus:         1
service:
  name:          snowy-river-gotjeojl
  uuid:          287ee3b8-43bc-47d1-a88e-4d6c72d2d682
  domains:
  - fqdn:        snowy-river-gotjeojl.fra.unikraft.app
networks:
- uuid:          107e4a03-e285-4d1d-84cb-24f86d7af875
  private-ip:    10.0.14.201
  mac:           12:b0:0a:00:0e:c9
timestamps:
  created:       just now
scale-to-zero:
  enabled:       true
  policy:        on
  cooldown-time: 1s

You can list all deployed instances with:

Code
unikraft instances list

Code
METRO  NAME         STATE    IMAGE           MEMORY  VCPUS  FQDN                                   CREATED
fra    nginx-jnpwi  standby  <my-org>/nginx  512MiB  1      snowy-river-gotjeojl.fra.unikraft.app  11 minutes ago
fra    flask-9a68z  standby  <my-org>/flask  1GiB    1      backend.internal                       12 minutes ago
fra    mongo-o3qhq  standby  <my-org>/mongo  1GiB    1      mongo.internal                         14 minutes ago

Test the deployment

The FQDN of the NGINX instance can be found in the FQDN column of the unikraft instances list output above. Use curl to query it (replace with your actual FQDN):

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curl https://<FQDN>

Code
Hello from the MongoDB client!

Clean up

When done, remove the instances and volume:

Code
unikraft instances delete mongo-o3qhq flask-9a68z nginx-jnpwi
unikraft volume delete mongo-data

Learn more

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

Code
unikraft --help

Or visit the CLI Reference.

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Last modified on October 22, 2026

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