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88 lines
4.1 KiB
88 lines
4.1 KiB
.. _becomingbig: |
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Becoming Big |
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============ |
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Your application is becoming more and more complex? If you suddenly |
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realize that Flask does things in a way that does not work out for your |
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application there are ways to deal with that. |
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Flask is powered by Werkzeug and Jinja2, two libraries that are in use at |
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a number of large websites out there and all Flask does is bring those |
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two together. Being a microframework Flask does not do much more than |
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combining existing libraries - there is not a lot of code involved. |
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What that means for large applications is that it's very easy to take the |
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code from Flask and put it into a new module within the applications and |
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expand on that. |
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Flask is designed to be extended and modified in a couple of different |
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ways: |
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- Flask extensions. For a lot of reusable functionality you can create |
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extensions. For extensions a number of hooks exist throughout Flask |
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with signals and callback functions. |
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- Subclassing. The majority of functionality can be changed by creating |
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a new subclass of the :class:`~flask.Flask` class and overriding |
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methods provided for this exact purpose. |
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- Forking. If nothing else works out you can just take the Flask |
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codebase at a given point and copy/paste it into your application |
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and change it. Flask is designed with that in mind and makes this |
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incredible easy. You just have to take the package and copy it |
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into your application's code and rename it (for example to |
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`framework`). Then you can start modifying the code in there. |
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Why consider Forking? |
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--------------------- |
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The majority of code of Flask is within Werkzeug and Jinja2. These |
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libraries do the majority of the work. Flask is just the paste that glues |
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those together. For every project there is the point where the underlying |
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framework gets in the way (due to assumptions the original developers |
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had). This is natural because if this would not be the case, the |
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framework would be a very complex system to begin with which causes a |
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steep learning curve and a lot of user frustration. |
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This is not unique to Flask. Many people use patched and modified |
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versions of their framework to counter shortcomings. This idea is also |
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reflected in the license of Flask. You don't have to contribute any |
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changes back if you decide to modify the framework. |
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The downside of forking is of course that Flask extensions will most |
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likely break because the new framework has a different import name. |
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Furthermore integrating upstream changes can be a complex process, |
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depending on the number of changes. Because of that, forking should be |
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the very last resort. |
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Scaling like a Pro |
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------------------ |
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For many web applications the complexity of the code is less an issue than |
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the scaling for the number of users or data entries expected. Flask by |
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itself is only limited in terms of scaling by your application code, the |
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data store you want to use and the Python implementation and webserver you |
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are running on. |
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Scaling well means for example that if you double the amount of servers |
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you get about twice the performance. Scaling bad means that if you add a |
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new server the application won't perform any better or would not even |
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support a second server. |
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There is only one limiting factor regarding scaling in Flask which are |
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the context local proxies. They depend on context which in Flask is |
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defined as being either a thread, process or greenlet. If your server |
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uses some kind of concurrency that is not based on threads or greenlets, |
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Flask will no longer be able to support these global proxies. However the |
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majority of servers are using either threads, greenlets or separate |
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processes to achieve concurrency which are all methods well supported by |
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the underlying Werkzeug library. |
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Dialogue with the Community |
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--------------------------- |
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The Flask developers are very interested to keep everybody happy, so as |
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soon as you find an obstacle in your way, caused by Flask, don't hesitate |
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to contact the developers on the mailinglist or IRC channel. The best way |
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for the Flask and Flask-extension developers to improve it for larger |
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applications is getting feedback from users.
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