Don't use max_age if Flask version is <2.0

[kevingreer]

Related Issues/PRs

Resolve #8456

What changes are proposed in this pull request?

The max_age keyword in flask.send_from_directory was introduced in Flask 2.0, which makes MLflow currently require Flask>=2.0. This PR checks what version of Flask is running and uses the old kwarg name if Flask is older than 2.0.

How is this patch tested?

(1) Run yarn build in mlflow/server/js to build the artifacts needed to run the UI
(2) Create a Dockerfile:

FROM python:3.8.10

RUN pip install flask==1.* && \
    # Other pins needed to get Flask<2 to work (with MLflow<2.3 but not 2.3)
    pip install jinja2==3.0.3 && \
    pip install itsdangerous==2.0.1 && \
    pip install werkzeug==2.0.3 && \
    pip install markupsafe==2.0.1

# RUN pip install mlflow==2.3.1
COPY mlflow/ ./mlflow
RUN pip install ./mlflow

EXPOSE 5000

CMD mlflow server --host 0.0.0.0 --port 5000

Build and run the image:

docker build -f Dockerfile . -t mlflow-issue-8456
docker run -p 5000:5000 mlflow-issue-8456:latest

Then navigate to 0.0.0.0:5000. Without this change there is an error and a blank page is shown. With this change the UI is shown.

• Existing unit/integration tests
• New unit/integration tests
• Manual tests (describe details, including test results, below)

Does this PR change the documentation?

• No. You can skip the rest of this section.
• Yes. Make sure the changed pages / sections render correctly in the documentation preview.

Release Notes

Is this a user-facing change?

• No. You can skip the rest of this section.
• Yes. Give a description of this change to be included in the release notes for MLflow users.

Fix a bug that made MLflow mistakenly require Flask>=2.0

What component(s), interfaces, languages, and integrations does this PR affect?

Components

• area/artifacts: Artifact stores and artifact logging
• area/build: Build and test infrastructure for MLflow
• area/docs: MLflow documentation pages
• area/examples: Example code
• area/model-registry: Model Registry service, APIs, and the fluent client calls for Model Registry
• area/models: MLmodel format, model serialization/deserialization, flavors
• area/recipes: Recipes, Recipe APIs, Recipe configs, Recipe Templates
• area/projects: MLproject format, project running backends
• area/scoring: MLflow Model server, model deployment tools, Spark UDFs
• area/server-infra: MLflow Tracking server backend
• area/tracking: Tracking Service, tracking client APIs, autologging

Interface

• area/uiux: Front-end, user experience, plotting, JavaScript, JavaScript dev server
• area/docker: Docker use across MLflow's components, such as MLflow Projects and MLflow Models
• area/sqlalchemy: Use of SQLAlchemy in the Tracking Service or Model Registry
• area/windows: Windows support

Language

• language/r: R APIs and clients
• language/java: Java APIs and clients
• language/new: Proposals for new client languages

Integrations

• integrations/azure: Azure and Azure ML integrations
• integrations/sagemaker: SageMaker integrations
• integrations/databricks: Databricks integrations

How should the PR be classified in the release notes? Choose one:

• rn/breaking-change - The PR will be mentioned in the "Breaking Changes" section
• rn/none - No description will be included. The PR will be mentioned only by the PR number in the "Small Bugfixes and Documentation Updates" section
• rn/feature - A new user-facing feature worth mentioning in the release notes
• rn/bug-fix - A user-facing bug fix worth mentioning in the release notes
• rn/documentation - A user-facing documentation change worth mentioning in the release notes

[WeichenXu123]

LGTM

[github-actions]

@kevingreer Thank you for the contribution! Could you fix the following issue(s)?

⚠ DCO check

The DCO check failed. Please sign off your commit(s) by following the instructions here. See https://github.com/mlflow/mlflow/blob/master/CONTRIBUTING.md#sign-your-work for more details.

[mlflow-automation]

Documentation preview for 9ba5470 will be available here when this CircleCI job completes successfully.

More info

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• This comment was created by https://github.com/mlflow/mlflow/actions/runs/5042321965.

[kevingreer]

The lint failure is unrelated to my change but I could change it if we want, please let me know.

[harupy]

I think it's related. Can you move from packaging.version import Version above from flask import __version__ as flask_version?