fastapi + newrelic mcve with late license_key plugging bug

app.py

#import os
#os.environ["NEW_RELIC_LICENSE_KEY"] = "some_valid_key"

import sys
import logging
logging.basicConfig(stream=sys.stdout, level=logging.INFO)

import newrelic.agent

newrelic.agent.initialize("newrelic.ini")
newrelic.agent.global_settings().license_key = "some_valid_key"
newrelic.agent.register_application()


import fastapi

app = fastapi.FastAPI()
@app.get("/")
async def health():
    return "hello world!"

newrelic.ini

[newrelic]
app_name = HelloWorld
monitor_mode = true

requirements.txt

fastapi==0.60.2
newrelic==5.22.0.151
uvicorn==0.12.2

Set up virtual env, activate it, install dependencies, and run server:

$ python -m venv venv
$ source venv/bin/activate
(venv)$ pip install -r requirements.txt
(venv)$ uvicorn app:app 

Should result in

CRITICAL:newrelic.core.agent_protocol:Disconnection of the agent has been requested by the data collector for the application where the agent run was None. Please contact New Relic support for further information.

Using os.environ to plug in the license on the other hand:

INFO:newrelic.core.agent_protocol:Reporting to: https://rpm.eu.newrelic.com/accounts/xxxxx/applications/xxxxxx

Found the solution: If using an EU based license key, you need to set the host together with the license:

newrelic.agent.initialize("newrelic.ini")
newrelic.agent.global_settings().license_key = "some_valid_key"
newrelic.agent.global_settings().host = newrelic.core.config.default_host("some_valid_key")  # EU-only
newrelic.agent.register_application()

Cheers to a-feld for debugging it for me.