Front-end caching and session back end

Front-end caching and session back end

Front-end caching

We do not recommend using front-end caching tools with the dashboard. The dashboard is rendering dynamic content resulting directly from OpenStack API requests and front-end caching layers such as varnish can prevent the correct content from being displayed. In Django, static media is directly served from Apache or Nginx and already benefits from web host caching.

Session back end

The default session back end for horizon django.contrib.sessions.backends.signed_cookies saves user data in signed, but unencrypted cookies stored in the browser. Due to the fact that each dashboard instance is stateless, the previously mentioned methodology provides the ability to implement the most simple session back-end scaling.

It should be noted that with this type of implementation sensitive access tokens will be stored in the browser and will be transmitted with each request made. The back end ensures the integrity of session data, even though the transmitted data is only encrypted by HTTPS.

If your architecture allows for shared storage and and if you have configured your cache correctly, we recommend setting your SESSION_ENGINE to django.contrib.sessions.backends.cache and using it as cache-based session backend with memcached as the cache. Memcached is an efficient in-memory key-value store for chunks of data that can be used in a high availability and distributed environment and is easy to configure. However, you need to ensure that there is no data leakage. Memcached makes use of spare RAM to store frequently accessed data blocks, acting like memory cache for repeatedly accessed information. Since memcached utilizes local memory, there is no overhead of database and file system usage leading to direct access of data from RAM rather than from disk.

We recommend the use of memcached instead of local-memory cache because it is fast, retains data for a longer duration, is multi-process safe and has the ability to share cache over multiple servers, but still treats it as a single cache.

To enable memcached, execute the following:

SESSION_ENGINE = 'django.contrib.sessions.backends.cache'
    'BACKEND': 'django.core.cache.backends.memcached.MemcachedCache'

For further details, see the Django documentation.

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