Flask-S3 has two main functions:
- Walk through your application’s static folders, gather all your static assets together, and upload them to a bucket of your choice on S3;
- Replace the URLs that Flask’s flask.url_for() function would insert into your templates, with URLs that point to the static assets in your S3 bucket.
The process of gathering and uploading your static assets to S3 need only be done once, and your application does not need to be running for it to work. The location of the S3 bucket can be inferred from Flask-S3 settings specified in your Flask application, therefore when your application is running there need not be any communication between the Flask application and Amazon S3.
Internally, every time url_for is called in one of your application’s templates, flask_s3.url_for is instead invoked. If the endpoint provided is deemed to refer to static assets, then the S3 URL for the asset specified in the filename argument is instead returned. Otherwise, flask_s3.url_for passes the call on to flask.url_for.
If you use pip then installation is simply:
$ pip install flask-s3
or, if you want the latest github version:
$ pip install git+git://github.com/e-dard/flask-s3.git
You can also install Flask-S3 via Easy Install:
$ easy_install flask-s3
Flask-S3 is incredibly simple to use. In order to start serving your Flask application’s assets from Amazon S3, the first thing to do is let Flask-S3 know about your flask.Flask application object.
from flask import Flask from flask_s3 import FlaskS3 app = Flask(__name__) app.config['S3_BUCKET_NAME'] = 'mybucketname' s3 = FlaskS3(app)
In many cases, however, one cannot expect a Flask instance to be ready at import time, and a common pattern is to return a Flask instance from within a function only after other configuration details have been taken care of. In these cases, Flask-S3 provides a simple function, init_app, which takes your application as an argument.
from flask import Flask from flask_s3 import FlaskS3 s3 = FlaskS3() def start_app(): app = Flask(__name__) s3.init_app(app) return app
In terms of getting your application to use external Amazon S3 URLs when referring to your application’s static assets, passing your Flask object to the FlaskS3 object is all that needs to be done. Once your app is running, any templates that contained relative static asset locations, will instead contain hosted counterparts on Amazon S3.
You only need to upload your static assets to Amazon S3 once. Of course, if you add or modify your existing assets then you will need to repeat the uploading process.
Uploading your static assets from a Python console is as simple as follows.
>>> import flask_s3 >>> from my_application import app >>> flask_s3.create_all(app) >>>
Flask-S3 will proceed to walk through your application’s static assets, including those belonging to registered blueprints, and upload them to your Amazon S3 bucket.
Within your bucket on S3, Flask-S3 replicates the static file hierarchy defined in your application object and any registered blueprints. URLs generated by Flask-S3 will look like the following:
/static/foo/style.css becomes https://mybucketname.s3.amazonaws.com/static/foo/style.css, assuming that mybucketname is the name of your S3 bucket, and you have chosen to have assets served over HTTPS.
Within your Flask application’s settings you can provide the following settings to control the behvaiour of Flask-S3. None of the settings are required, but if not present, some will need to be provided when uploading assets to S3.
|AWS_ACCESS_KEY_ID||Your AWS access key. This does not need to be stored in your configuration if you choose to pass it directly when uploading your assets.|
|AWS_SECRET_ACCESS_KEY||Your AWS secret key. As with the access key, this need not be stored in your configuration if passed in to create_all.|
|S3_BUCKET_DOMAIN||The domain part of the URI for your S3 bucket. You probably won’t need to change this. Default: u's3.amazonaws.com'|
|S3_BUCKET_NAME||The desired name for your Amazon S3 bucket. Note: the name will be visible in all your assets’ URLs.|
|S3_USE_HTTPS||Specifies whether or not to serve your assets stored in S3 over HTTPS. Default: True|
|USE_S3||This setting allows you to toggle whether Flask-S3 is active or not. When set to False your application’s templates will revert to including static asset locations determined by flask.url_for. Default: True|
|USE_S3_DEBUG||By default, Flask-S3 will be switched off when running your application in debug mode, so that your templates include static asset locations specified by flask.url_for. If you wish to enable Flask-S3 in debug mode, set this value to True. Note: if USE_S3 is set to False then templates will always include asset locations specified by flask.url_for.|
Flask-S3 is a very simple extension. The few exposed objects, methods and functions are as follows.
The FlaskS3 object allows your application to use Flask-S3.
|Parameters:||app (flask.Flask or None) – optional flask.Flask application object|
Uploads of the static assets associated with a Flask application to Amazon S3.
All static assets are identified on the local filesystem, including any static assets associated with registered blueprints. In turn, each asset is uploaded to the bucket described by bucket_name. If the bucket does not exist then it is created.
Flask-S3 creates the same relative static asset folder structure on S3 as can be found within your Flask application.
Generates a URL to the given endpoint.
If the endpoint is for a static resource then an Amazon S3 URL is generated, otherwise the call is passed on to flask.url_for.
Because this function is set as a jinja environment variable when FlaskS3.init_app is invoked, this function replaces flask.url_for in templates automatically. It is unlikely that this function will need to be directly called from within your application code, unless you need to refer to static assets outside of your templates.