Flask Auto Instrumentation dissapears on debug=True app reload

Describe your environment
python 3.9
flask~=1.0
opentelemetry-api==1.3.0
opentelemetry-sdk==1.3.0
opentelemetry-instrumentation==0.22b0
opentelemetry-instrumentation-flask==0.22b0

Steps to reproduce

I created a very simple flask app my_app.py with either debug=False or debug=True:

from flask import Flask
from opentelemetry import trace

# Setup Flask App

app = Flask(__name__)

@app.route("/my_endpoint")
def call_http():
    return '{{"traceId": "{}"}}'.format(
        trace.get_current_span().get_span_context().trace_id
    )


if __name__ == "__main__":
    app.run(**{"port": 8080, "debug": False})

I then use auto-instrumentation to instrument the app with the ConsoleExporter:

opentelemetry-instrument --trace-exporter console_span python3 my_app.py

What is the expected behavior?

If I use debug=False everything works fine.

Console output:

{
    "name": "/my_endpoint",
    "context": {
        "trace_id": "0x317a86be6e1cbe5fa913f003154f2a32",
        "span_id": "0x2aafb7284d6168ea",
        "trace_state": "[]"
    },
    "kind": "SpanKind.SERVER",
    "parent_id": null,
    "start_time": "2021-06-22T17:08:52.484880Z",
    "end_time": "2021-06-22T17:08:52.485936Z",
    "status": {
        "status_code": "UNSET"
    },
    "attributes": {
        "http.method": "GET",
        "http.server_name": "127.0.0.1",
        "http.scheme": "http",
        "net.host.port": 8080,
        "http.host": "localhost:8080",
        "http.target": "/my_endpoint",
        "net.peer.ip": "127.0.0.1",
        "http.user_agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Firefox/78.0",
        "net.peer.port": 49317,
        "http.flavor": "1.1",
        "http.route": "/my_endpoint",
        "http.status_code": 200
    },
    "events": [],
    "links": [],
    "resource": {
        "telemetry.sdk.language": "python",
        "telemetry.sdk.name": "opentelemetry",
        "telemetry.sdk.version": "1.3.0",
        "service.name": "unknown_service"
    }
}

Browser response is OK:

What is the actual behavior?

If I use debug=True it does not work

No console output:

No trace id that can be returned in the response:

Additional context

I used print statements to confirm that auto instrumentation does run and replace the right methods before the app starts. But when the Restarting with stat message appears it seems like the instrumentation is lost.

The fix might require investigating how auto reloader works and instrumenting some hidden "clean slate app" that the auto reloader replaces the currently running app with to restart the instrumentation.

Reproduce the issue with my_app.py using the opentelemetry-instrument command and Flask debug=True, then compare behavior before and after the reloader prints its restart message. Investigate how Flask's auto reloader replaces the running application and verify that auto-instrumentation remains active afterward, with request spans exported and a trace ID returned.