Flask Cache not caching

Question

I followed a tutorial of Flask-Cache and tried to implement it myself. Given the following example, why would Flask not cache the time?

from flask import Flask
import time

app = Flask(__name__)
cache = Cache(config={'CACHE_TYPE': 'simple'})
cache.init_app(app)

@app.route('/time')
@cache.cached(timeout=50, key_prefix='test')
def test():
   return time.ctime()

Output is always the current time.

It seems like the cache is recreated every single request. What am I doing wrong?

Edit: I execute the following python-file with Python 2.7.6:

def runserver():
    port = int(os.environ.get('PORT', 5000))
    Triangle(app)
    app.run(host='0.0.0.0', port=port, processes=5)


if __name__ == '__main__':
    runserver()

Answer 1

You are using the SimpleCache setup:

cache = Cache(config={'CACHE_TYPE': 'simple'})

This uses a single global dictionary to hold the cache, and this in turn will only work if you are using a WSGI server that uses one Python interpreter to serve all your WSGI requests. If you use a WSGI server that uses separate child processes to handle requests, you'll get a new copy of that dictionary each time and nothing is cached, effectively.

The code works fine when run with the built-in app.run() development server, given you don't use the processes argument.

Your update shows that you run the server with 5 separate processes. Each process will get its own dictionary, and the cache is not shared between them. Use a different caching backend instead, like filesystem:

cache = Cache(config={'CACHE_TYPE': 'filesystem', 'CACHE_DIR': '/tmp'})