Document how to work with fork process web server models(Gunicorn, uWSGI etc...)

[srikanthccv]

Description

Add how to work with fork process web server models(Gunicorn, uWSGI etc...)

Fixes open-telemetry/opentelemetry-python-contrib#291

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How Has This Been Tested?

• tox -e docs
• tox -e lint

Does This PR Require a Contrib Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated
• Documentation has been updated

[srikanthccv]

@owais Updated the examples and documentation. PTAL.

[owais]

LGTM. Thanks

[ash-ishh]

Hello!

Should there be disclaimer stating that if environment variable like OTEL_PYTHON_FLASK_EXCLUDED_URLS are defined in gunicorn.config.py or app.py then the filtering won't work.

Reason: ExcludeList is initialized on from opentelemetry.sdk.trace import TracerProvider import and environment variable is being set post initalization.

Examples where filtering won't work:

gunicorn.conf.py

import os
...
def post_fork(server, worker):
    server.log.info("Worker spawned (pid: %s)", worker.pid)
    os.environ["OTEL_PYTHON_FLASK_EXCLUDED_URLS"] = "fibonacci"
    resource = Resource.create(attributes={"service.name": "api-service"})
...

app.py

import os
from opentelemetry import trace
from opentelemetry.instrumentation.flask import FlaskInstrumentor

application = flask.Flask(__name__)

FlaskInstrumentor().instrument_app(application)
os.environ["OTEL_PYTHON_FLASK_EXCLUDED_URLS"] = "fibonacci"
...

Examples where filtering will work:

app.py

import os
from opentelemetry import trace
os.environ["OTEL_PYTHON_FLASK_EXCLUDED_URLS"] = "fibonacci"
from opentelemetry.sdk.trace import TracerProvider
from opentelemetry.sdk.trace.export import BatchExportSpanProcessor
...

[srikanthccv]

@ash-ishh it isn't really related to this PR and to be precise the excluded urls list for third party packages is created when the instrumentations are imported eg: flask see here. It doesn't work if you import the instrumentation first and then set the env. This is the current behaviour for all the instrumentations irrespective the process models.

[ash-ishh]

Understood.. the reason I stumbled upon issue was because in Django while setting os.environ.setdefault("DJANGO_SETTINGS_MODULE", "app.settings") I also tried to set OTEL environment variable there only to keep all the enviroment configuration in one place

If in future enough people repeat the same mistake then maybe we might need to add disclaimer in django-instrumentation and flask-instrumentation documentation (will keep an eye on issues of those repos)

Sorry for raising the issue in wrong place and thanks for the clarification :)

[lzchen]

@ocelotl
Please review again.

[ocelotl]

@ocelotl
Please review again.

Reviewed 👍