Simple FastApi App Example on Open Telekom Cloud

This is a simple example on how to create a FastApi application and deploy it as FunctionGraph HTTP function on Open Telekom Cloud.

Requirements

  • Unix-like environment (Linux or WSL on Windows)

  • Python 3.10

  • Python virtual environment

  • Open Telekom Cloud account

Create FastAPI App

mkdir otc-fastapi-app

cd otc-fastapi-app

python3 -m venv .venv

source .venv/bin/activate

# Install FastAPI and Uvicorn
python3 -m pip install fastapi[standard] uvicorn

mkdir src

Add app.py file in src directory

src/app.py
from fastapi import FastAPI

app = FastAPI()

@app.get("/")
async def read_root():
    return {"message": "Hello World of FastAPI on OTC!"}

if __name__ == "__main__":
    import uvicorn

    # On OpenTelekomCloud FunctionGraph port must be 8000
    uvicorn.run("app:app", port=8000, log_level="debug", reload=True, host="localhost")

Run FastAPI app.py locally

cd src

python3 app.py

Open browser with http://localhost:8000/docs

simpleFastApiLocalhost.png

You can test your endpoint by clicking on the GET / Read Root route and then clicking execute.

Deploy FastAPI app as FunctionGraph HTTP function

Create deployment package

Create bootstrap file

The bootstrap file is the startup file of the HTTP function. The HTTP function can only read bootstrap as the startup file name from the root of the deployment package.

Additional to the startup of the FastAPI app, the bootstrap file must set the PYTHONPATH to include the dependencies folder.

bootstrap
export PYTHONPATH=${PYTHONPATH}:${RUNTIME_CODE_ROOT}/dependencies
/opt/function/runtime/python3.10/rtsp/python/bin/python3 $RUNTIME_CODE_ROOT/src/app.py

Create deployment zip file

The structure of the zip file must be like:

structure of zip file
  .
  ├── bootstrap
  ├── dependencies
  │   ├── <all dependencies installed in venv>
  └── src
      └── app.py

The following commands create a zip file containing the dependencies folder, the src folder and the bootstrap file:

Commands to zip for deployment
  rm -r -f target
  mkdir -p target/zip_content/dependencies
  mkdir -p target/zip_content/src
  cp -R .venv/lib/python3.10/site-packages/* target/zip_content/dependencies
  cp -R src target/zip_content
  cp -R bootstrap target/zip_content

  (export TARGET=${PWD}/target && cd target/zip_content && zip -r ${TARGET}/code.zip . --exclude \*__pycache__\*)

Create FunctionGraph HTTP function on Open Telekom Cloud

Login to the FunctionGraph console and click on Create Function.

Create Function

Select Create from scratch and as function type select HTTP function, choose a name for your function (e.g. simpleFastApi) and click on Create Function:

Select HTTP function

Now upload the zip file created before (target/code.zip) using the Upload - Local ZIP button:

Upload code

To test the function, create a test event using the Test button:

Upload code

Choose API Gateway (Dedicated) from the Event Template List.

You can use the sample test event below (see next code block). Choose a name for the test event (e.g. root) and click on OK.

Create test event

The adaption in the test event is the

  • "httpMethod" = “GET” (line 11) and

  • "path" = “/” (line 27)

field to match your FastAPI endpoint:

sample test event
 1  {
 2      "body": "",
 3      "requestContext": {
 4          "apiId": "bc1dcffd-aa35-474d-897c-d53425a4c08e",
 5          "requestId": "11cdcdcf33949dc6d722640a13091c77",
 6          "stage": "RELEASE"
 7      },
 8      "queryStringParameters": {
 9          "responseType": "html"
10      },
11      "httpMethod": "GET",
12      "pathParameters": {},
13      "headers": {
14          "accept-language": "q=0.5,en-US;q=0.3,en;q=0.2",
15          "accept-encoding": "gzip, deflate, br",
16          "x-forwarded-port": "443",
17          "x-forwarded-for": "103.218.216.98",
18          "accept": "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8",
19          "upgrade-insecure-requests": "1",
20          "host": "host",
21          "x-forwarded-proto": "https",
22          "pragma": "no-cache",
23          "cache-control": "no-cache",
24          "x-real-ip": "103.218.216.98",
25          "user-agent": "Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:57.0) Gecko/20100101 Firefox/57.0"
26      },
27      "path": "/",
28      "isBase64Encoded": true
29  }

and click on Create.

Now you can execute the test event using the Test button.

The result of the execution is shown below:

Create test run

The full execution result is shown below:

Execution result
  {
      "body": "eyJtZXNzYWdlIjoiSGVsbG8gV29ybGQgb2YgRmFzdEFQSSBvbiBPVEMhIn0=",
      "headers": {
          "Content-Length": [
              "44"
          ],
          "Content-Type": [
              "application/json"
          ],
          "Date": [
              "Tue, 23 Sep 2025 10:59:49 GMT"
          ],
          "Server": [
              "uvicorn"
          ]
      },
      "statusCode": 200,
      "isBase64Encoded": true
  }

The body is base64 encoded, to decode the body use following command:

decode body
  echo "eyJtZXNzYWdlIjoiSGVsbG8gV29ybGQgb2YgRmFzdEFQSSBvbiBPVEMhIn0=" | base64 --decode

  # response
  {"message":"Hello World of FastAPI on OTC!"}

Outlook

You can now create an API Gateway trigger together with an API Gateway to call your FunctionGraph HTTP function from outside the Open Telekom Cloud.

For a full example including API Gateway and Terraform, see Sample.

last updated: 2026-09-22 13:40:45 UTC - commit: 82fab280aa0875971130a598f73d8a6997d954f9