# Flask HTTP Server

import { Tabs, TabsContent, TabsList, TabsTrigger } from "zudoku/ui/Tabs"

{/* vale off */}
{/* THIS FILE WAS AUTOGENERATED FROM THE PUBLIC EXAMPLE REPOSITORY. DO NOT EDIT THIS FILE DIRECTLY. */}


This guide explains how to create and deploy a [Flask](https://flask.palletsprojects.com/en/3.0.x/) web server.
To run this example, follow these steps:

1. Install the CLI.
   Use the [unikraft CLI](/cli/unikraft) or the legacy [kraft CLI](https://unikraft.org/docs/cli/install).
   You need a [BuildKit](https://github.com/moby/buildkit) builder. The easiest way to get one is via [Docker](https://docs.docker.com/engine/install/).
   Alternatively, you can also directly set up and use BuildKit, see the [quick start](https://github.com/moby/buildkit#quick-start).

   :::note
   The unikraft CLI is the current standard, while kraft is the legacy version.
   Choose one of the CLIs below and only run the commands associated with it for the rest of this guide.
   :::

2. Clone the [`examples` repository](https://github.com/unikraft-cloud/examples) and `cd` into the `examples/httpserver-python3.12-flask3.0/` directory:

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

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

<CodeTabs syncKey="cli">

```bash title="unikraft"
unikraft login
```

```bash title="kraft"
# Set Unikraft Cloud access token
export UKC_TOKEN=token
# Set metro to Frankfurt, DE
export UKC_METRO=fra
```

</CodeTabs>

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

<CodeTabs syncKey="cli">

```bash title="unikraft"
unikraft build . --output <my-org>/httpserver-python312-flask30:latest
unikraft run --metro fra \
  -m 512M \
  -p 443:8080/tls+http \
  --scale-to-zero policy=on,cooldown-time=1000 \
  --image <my-org>/httpserver-python312-flask30:latest
```

```bash title="kraft"
kraft cloud deploy \
  -M 512Mi \
  -p 443:8080/tls+http \
  --scale-to-zero on \
  --scale-to-zero-cooldown 1s \
  .
```

</CodeTabs>

The output shows the instance address and other details:

<CodeTabs syncKey="cli">

```ansi title="unikraft"
[1mmetro[22m:        fra
[1mname[22m:         httpserver-python312-flask30-bxwxm
[1muuid[22m:         3ff1ebad-2639-4214-bab4-ed35c4c32fa4
[1mstate[22m:        [38;2;144;161;185mstarting[0m
[1mimage[22m:        <my-org>/httpserver-python312-flask30
[1mresources[22m:
[3m  memory[23m:     512MiB
[3m  vcpus[23m:      1
[1mservice[22m:
[3m  uuid[23m:       2021ca1e-5e47-a35c-bde2-7190f3815c07
[3m  name[23m:       damp-sunset-azd6dtyt
[3m  domains[23m:
[3m  - fqdn[23m:     damp-sunset-azd6dtyt.fra.unikraft.app
[1mnetworks[22m:
[3m- uuid[23m:       4dc3b272-4fa2-ddb4-7ce0-5e66e8112a61
[3m  private-ip[23m: 10.0.6.5
[3m  mac[23m:        12:b0:66:99:b3:3f
[1mtimestamps[22m:
[3m  created[23m:    just now
```

```ansi title="kraft"
[38;5;245m[[0m[92m●[0m[38;5;245m][0m Deployed successfully!
 [38;5;245m│[0m
 [38;5;245m├[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m [38;5;245mname[0m: httpserver-python312-flask30-bxwxm
 [38;5;245m├[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m [38;5;245muuid[0m: 3ff1ebad-2639-4214-bab4-ed35c4c32fa4
 [38;5;245m├[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m [38;5;245mmetro[0m: https://api.fra.unikraft.cloud/v1
 [38;5;245m├[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m [38;5;245mstate[0m: [92mstarting[0m
 [38;5;245m├[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m [38;5;245mdomain[0m: https://damp-sunset-azd6dtyt.fra.unikraft.app
 [38;5;245m├[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m [38;5;245mimage[0m: oci://unikraft.io/<my-org>/httpserver-python312-flask30@sha256:d6c8e4c5a4f44e1d642d8eaeaa1d820b2841194dd6c5d4a872ae0a895c767da9
 [38;5;245m├[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m [38;5;245mmemory[0m: 512 MiB
 [38;5;245m├[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m [38;5;245mservice[0m: damp-sunset-azd6dtyt
 [38;5;245m├[0m[38;5;245m─[0m [38;5;245mprivate fqdn[0m: httpserver-python312-flask30-bxwxm.internal
 [38;5;245m└[0m[38;5;245m─[0m[38;5;245m─[0m[38;5;245m─[0m [38;5;245mprivate ip[0m: 10.0.6.5
```

</CodeTabs>

In this case, the instance name is `httpserver-python312-flask30-bxwxm` and the address is `https://damp-sunset-azd6dtyt.fra.unikraft.app`.
They're different for each run.

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

```bash
curl https://damp-sunset-azd6dtyt.fra.unikraft.app
```

```text
Hello, World!
```

You can list information about the instance by running:

<CodeTabs syncKey="cli">

```bash title="unikraft"
unikraft instances list
```

```bash title="kraft"
kraft cloud instance list
```

</CodeTabs>

<div style={{ marginTop: '0.8em' }} />

<CodeTabs syncKey="cli">

```ansi title="unikraft"
[1mMETRO[22m  [1mNAME[22m                                [1mSTATE[22m    [1mIMAGE[22m                                  [1mARGS[22m  [1mMEMORY[22m  [1mVCPUS[22m  [1mFQDN[22m                                   [1mCREATED[22m
fra    httpserver-python312-flask30-bxwxm  [38;2;0;188;125mrunning[0m  <my-org>/httpserver-python312-flask30        512MiB  1      damp-sunset-azd6dtyt.fra.unikraft.app  2 minutes ago
```

```ansi title="kraft"
[0;1;39mNAME[0m                                [0;1;39mFQDN[0m                                   [0;1;39mSTATE[0m    [0;1;39mSTATUS[0m        [0;1;39mIMAGE[0m                                                               [0;1;39mMEMORY[0m   [0;1;39mVCPUS[0m  [0;1;39mARGS[0m  [0;1;39mBOOT TIME[0m
httpserver-python312-flask30-bxwxm  damp-sunset-azd6dtyt.fra.unikraft.app  [0;32mrunning[0m  1 minute ago  oci://unikraft.io/<my-org>/httpserver-python312-flask30@sha256:...  512 MiB  1            222.27 ms
```

</CodeTabs>

When done, you can remove the instance:

<CodeTabs syncKey="cli">

```bash title="unikraft"
unikraft instances delete httpserver-python312-flask30-bxwxm
```

```bash title="kraft"
kraft cloud instance remove httpserver-python312-flask30-bxwxm
```

</CodeTabs>

## Customize your app

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

* `server.py`: the actual Python HTTP server
* `Kraftfile`: the Unikraft Cloud specification
* `Dockerfile`: the Docker-specified app filesystem

Lines in the `Kraftfile` have the following roles:

* `spec: v0.7`: The current `Kraftfile` specification version is `0.7`.

* `runtime: base-compat:latest`: The runtime kernel to use is the base compatibility kernel.

* `rootfs`: Build the app root filesystem.
  `source: ./Dockerfile` means the filesystem is built using the `Dockerfile`.
  `format: erofs` means the filesystem type is [EROFS](https://erofs.docs.kernel.org/).

* `cmd: ["/usr/bin/python3", "/src/server.py"]`: Use `/usr/bin/python3 /src/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](https://hub.docker.com/_/scratch/), to [create a base image](https://docs.docker.com/build/building/base-images/).

* `COPY ./server.py /app/server.py`: Copy the server implementation file (`server.py`) in the Docker filesystem (in `/app/server.py`).

The following options are available for customizing the app:

* If you only update the implementation in the `server.py` source file, 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`.

* More extensive changes may require extending the `Dockerfile` ([see `Dockerfile` syntax reference](https://docs.docker.com/engine/reference/builder/)).
  This includes the use of Python frameworks and the use of `pip`, as shown in the next section.

## Using `pip`

[`pip`](https://pip.pypa.io/en/stable/) is a package manager for Python.
It's used to install dependencies for Python apps.
`pip` uses the `requirements.txt` file to list required dependencies (with versions).

To create an `pip`-based app:

1. Add the `requirements.txt` file used by `pip`.

2. Add framework-specific source files.
   In this case, this means the `server.py` file.

3. Update the `Dockerfile` to:

   3.1. `COPY` the local files.

   3.2. `RUN` the `pip3 install` command to install dependencies.

   3.3. `COPY` of the resulting and required files (`/usr/local/lib/python3.12` and `server.py`) in the app filesystem, using the [`scratch` container](https://hub.docker.com/_/scratch/).

The following lists the files:

The `requirements.txt` file lists the `flask` dependency.

The `Kraftfile` is the same one used for `httpserver-python3.12`.

For `Dockerfile` newly added lines have the following roles:

* `FROM python:3.12-bookworm AS base`: Use the base image of the `python:3.12-bookworm` container.
  This provides the `pip3` binary and other Python-related components.
  Name the current image `base`.

* `WORKDIR /app`: Use `/app` as working directory.
  All other commands in the `Dockerfile` run inside this directory.

* `COPY requirements.txt /app`: Copy the package configuration file to the Docker filesystem.

* `RUN pip3 install ...`: Install `pip` components listed in `requirements.txt`.

* `COPY --from=base ...`: Copy generated Python files in the new `base` image in the `scratch`-based image.

Similar actions apply to other `pip3`-based apps.

## Learn more

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

<CodeTabs syncKey="cli">

```bash title="unikraft"
unikraft --help
```

```bash title="kraft"
kraft cloud --help
```

</CodeTabs>

Or visit the [CLI Reference](/cli/unikraft) or the [legacy CLI Reference](/cli/kraft/overview).
{/* vale on */}