Cherrys : a Redis backend for CherryPy sessions

CherryPy kicks some serious arse in the 'I am just a HTTP framework' category! As of version 3.2 it supports 4 types of storage for sessions by default:

• Ram
• File
• PostgreSQL
• Memcached

Redis is growing in popularity as an alternative to Memcached (and is fully supported on dotCloud!)

Installation

If you are not using pip yet. Install it and while you are at it consider using virtualenv too.

$ pip install cherrys

redis-py and CherryPy are required dependencies hence will be installed if necessary.

We recommend installing hiredis-py (a faster parser) as well.

$ pip install hiredis

Usage (and abusage)

To tell CherryPy which backend to use, we need to specify the storage_type for the sessions tool. You may want to read more about CherryPy configuration.

tools.sessions.storage_type : 'redis'

But CherryPy doesn't know Redis. Hence the first thing we need to do is add the cherrys RedisSession class to cherrypy.lib.sessions.

import cherrys
cherrypy.lib.sessions.RedisSession = cherrys.RedisSession

It is that simple!

Config dictionary

There are a few optional parameters you can set:

• host [127.0.0.1] (when is_sentinel this is host for sentinel service)
• port [6379] (when is_sentinel this is port for sentinel service)
• ssl [False] (for both sentinel and redis)
• db [0]
• prefix [""] (prepended to session id if given; useful when ACLs are enabled)
• user [None] (for old version of authentication can be set to empty string)
• password [None]
• lock_timeout [None] (None, or time in seconds until session lock expires)
• url [None] (alternative to host/port/ssl/db/user/password combination)

Sentinel-related additional (optional) parameters:

• is_sentinel [False]
• sentinel_pass [None]
• sentinel_service [None]
• tls_skip_verify [False]

A full config dictionary to activate Redis backed sessions would look like this.

config = {
    'tools.sessions.on' : True,
    'tools.sessions.storage_type' : 'redis',

    'tools.sessions.host': REDIS_HOST,
    'tools.sessions.port': REDIS_PORT,

    'tools.sessions.db': REDIS_DB,
    'tools.sessions.prefix': REDIS_PREFIX,
    'tools.sessions.user': REDIS_USER,
    'tools.sessions.password': REDIS_PASS,
    'tools.sessions.lock_timeout: LOCK_TIME_SECONDS,
}

A full config dictionary to activate RedisSentinelSSL backed sessions would look like this.

config = {
    'tools.sessions.on' : True,
    'tools.sessions.storage_type' : 'redis',

    'tools.sessions.host': REDIS_HOST,
    'tools.sessions.port': REDIS_PORT,
    'tools.sessions.ssl': True,

    'tools.sessions.db': REDIS_DB,
    'tools.sessions.prefix': REDIS_PREFIX,
    'tools.sessions.user': REDIS_USER,
    'tools.sessions.password': REDIS_PASS,
    'tools.sessions.lock_timeout: LOCK_TIME_SECONDS,

    'tools.sessions.is_sentinel': True,
    'tools.sessions.sentinel_pass': REDIS_SENTINEL_PASS,
    'tools.sessions.sentinel_service': REDIS_SENTINEL_SERVICENAME,
    'tools.sessions.tls_skip_verify': True,
}

Configuration via redis URL

As a shortcut a URL to the redis server can be provided as well.

import cherrys
config = {
    'tools.sessions.on' : True,
    # next setting removes the need for initializing `cherrypy.lib.sessions.RedisSession' above:
    'tools.sessions.storage_class' : cherrys.RedisSession,
    'tools.sessions.url': 'redis://your-name:your-pwd@redis-server:6379/2'
}

The number at the end of the URL ("2") denotes the redis database to be used.

Running unittests

Unittests require a running redis-server on localhost:6379 setup without any authentication in place.

Then install pytest into your current virtualenv and start it from your command line:

$ pip install pytest
$ pytest