Supervisor Cache

Cache arbitrary data in a Supervisor instance.

Overview

This package is an RPC extension for the Supervisor package that provides the ability to cache arbitrary data directly inside a Supervisor instance as key/value pairs.

For example, if you write a program that modifies Supervisor's runtime configuration with Twiddler, you might also use Supervisor Cache to store breadcrumbs of this having occurred that your program can easily fetch later.

Since data cached in a Supervisor instance survives only as long as that instance, using Supervisor Cache can prevent the synchronization headaches you might have using the filesystem or a database to accomplish the same task.

Installation

Download and extract, then install to Python's site-packages: 

$ sudo python setup.py install

After installing the package, you must modify your supervisord.conf file to register the cache interface: 

[rpcinterface:cache]
supervisor.rpcinterface_factory = supervisor_cache.rpcinterface:make_cache_rpcinterface

After modifying the supervisord.conf file, your Supervisor instance must be restarted for the cache interface to be loaded.

Usage

The cache functions allow key/value pairs to be stored and fetched. The following Python interpreter session demonstrates the usage.

First, a ServerProxy object must be configured. If supervisord is listening on an inet socket, ServerProxy configuration is simple: 

>>> import xmlrpclib
>>> s = xmlrpclib.ServerProxy('http://localhost:9001')

If supervisord is listening on a domain socket, ServerProxy can be configured with SupervisorTransport. The URL must still be supplied and be a valid HTTP URL to appease ServerProxy, but it is superfluous. 

>>> import xmlrpclib
>>> from supervisor.xmlrpc import SupervisorTransport
>>> s = xmlrpclib.ServerProxy('http://127.0.0.1/whatever', 
... SupervisorTransport('', '', 'unix:///path/to/supervisor.sock'))

Once ServerProxy has been configured appropriately, we can now exercise supervisor_cache: 

>>> s.cache.getKeys()
[]
>>> s.cache.store('foo', 'bar')
True
>>> s.cache.fetch('foo')
'bar'
>>> s.cache.getKeys()
['foo']

The key must be a string and cannot be zero-length. The value must also be a string but is permitted to be zero-length.

Please consult the inline source documentation for the specifics of each command available.

Warnings

Data is not discarded from the cache until it is explicitly deleted with the cache.delete() method. Data does not persist after Supervisor is shut down.

Your Supervisor instance should never be exposed to the outside world. It is quite easy to perform a denial of service attack by filling supervisor_cache with large amounts of data.