OpenCache
OpenCache is an experimental HTTP caching platform that utilises OpenFlow-enabled switches to provide transparent content delivery. It works in a controller-node architecture, described in the Architecture section.
Progress is quickly advancing, with a number of features to be implemented shortly (see TODO for more details).
Requirements
OpenCache is written for Python 2.7 and is tested on Unix platforms. It is recommended that pip is used to automatically install OpenCache and any additional dependencies.
The OpenCache controller uses the pymongo library to interact with a MongoDB database. pyzmq is required for internal ØMQ messaging. Backported from Python 3.2+ to Python 2.6-2.7, configparser is also used for allowing additional flexibility in configuration files.
Installation
pip
To install or upgrade pip, download get-pip.py.
Then run the following (which may require administrator access):
$ python get-pip.pyFor more detailed instructions and alternative installation methods, please visit the pip website.
opencache
OpenCache can be installed easily using pip and PyPi:
$ pip install opencache --preAs OpenCache is still in a pre-release phase, it is necessary to use the --pre flag at the moment (to retrieve any release).
Alternatively, distutils can be used to install OpenCache from source. Simply download the compressed repository, uncompress, and run:
$ python setup.py installRunning OpenCache
OpenCache is split into two parts: the controller and the node. See the Architecture section for more details.
To run the OpenCache controller, simply use:
$ opencache --controller --config="PATH_TO_CONFIG"Similarly, to run the OpenCache node, use:
$ opencache --node --config="PATH_TO_CONFIG"Sample configuration files are included in example\config directory for both a controller and a node (see controller.conf and node.conf respectively). Runtime output is written to both a log file and to stdout. The destination file for this log can be specified in the configuration file.
Updating
If you are using the OpenCache PyPi distribution, simply run --upgrade to update to the latest version:
$ pip install opencache --pre --upgradeArchitecture
OpenCache operates in a controller-node architecture. This means that each node is configured to connect to a single controller. This controller is then responsible for the behaviour of any nodes that connect to it. This creates a centralised point of control. A user (or application) can interact with an OpenCache deployment through this controller by using the JSON-RPC Interface.
The controller maintains the state of connected nodes. If a controller does not receive a message from a controller within a pre-determined time limit, the controller assumes the node is disconnected. Each node will maintain connectivity with the controller using periodic keep_alive messages.
JSON-RPC Interface
To interface with OpenCache, a standard JSON-RPC can be made to the controller. All requests must be sent via the HTTP POST method.
The following RPCs are used to interact with a an OpenCache deployment via a controller (more details for each method given below):
| method | params | result |
|---|---|---|
start |
{ ("expr" : <expr>), ("node" : <node>) } |
<boolean> |
stop |
{ ("expr" : <expr>), ("node" : <node>) } |
<boolean> |
pause |
{ ("expr" : <expr>), ("node" : <node>) } |
<boolean> |
fetch |
{ ("expr" : <expr>), ("node" : <node>) } |
<boolean> |
seed |
{ ("expr" : <expr>), ("node" : <node>) } |
<boolean> |
refresh |
{ ("expr" : <expr>), ("node" : <node>) } |
<boolean> |
stat |
{ ("expr" : <expr>), ("node" : <node>) } |
[<cache_hit>, <cache_miss>... ] |
Parameters in brackets are optional. If not included, a wildcard all (*) is used. A <node> can be either a single node, a vertical-bar-seperated (|) list of nodes or a wildcard (*) for all existing nodes. An <expr> can either be a single OpenCache expression, a vertical-bar-seperated (|) list of OpenCache expressions or a wildcard (*) to cache all HTTP traffic.
start
Start the given cache instances. Creates new instances if they do not exist, and restarts those that are paused.
Return Value: Returns a true result message on success or an error message on failure.
stop
Stop the given cache instances. Prevents them from responding to requests and terminates the running instance. Content is removed from disk.
Return Value: Returns a true result message on success or an error message on failure.
pause
Pause the given cache instances, temporarily stopping request handing but not removing content from disk. Restart again using start command.
Return Value: Returns a true result message on success or an error message on failure.
fetch
Fetch and retrieve an object from a remote location. Considered as 'pre-caching' content on the node, ready to serve subsequent requests. Similar to a 'cache-miss' event, where content is not present in the cache and must be retrieved.
Return Value: Returns a true result message on success or an error message on failure.
seed
Artifically add a number of fully resolved expressions to the given nodes. Each one of these expressions is seen as equivalent to each other, and will serve the same content given a request. For example, this feature can be used to define a single object, stored in multiple locations; with the use of seed, the object will only be stored once in each node, reducing storage utilisation.
Return Value: Returns a true result message on success or an error message on failure.
refresh
Manually request fresh statistics from given cache instances. Does not rely on periodic reporting. Useful if you want the most up to date statistics.
Return Value: Returns a true result message on success or an error message on failure.
stat
Return aggregate statistics for given cache instances. These stats are stored at the controller to reduce latency. Cache instances will periodically report stats back to the controller. To manually request fresh statistics from given cache instances, use the refresh command before this (it may also be necessary to insert a delay to ensure fresh statistics are received back to the controller from all cache instances). Stats are kept for a predefined period of time that is configurable.
Return Value:
| field | note |
|---|---|
start |
number of cache instances in 'start' state. |
stop |
number of cache instances in 'stop' state. |
pause |
number of cache instances in 'paused' state. |
cache_miss |
number of cache miss (content not found in cache) events (one per request). |
cache_miss_size |
number of bytes served whilst handling cache miss (content not found in cache) events. |
cache_hit |
number of cache hit (content already found in cache) events (one per request). |
cache_hit_size |
number of bytes served whilst handling cache hit (content already found in cache) events. |
cache_object |
number of objects currently stored by the cache. |
cache_object_size |
number of bytes for the cached objects on disk (actual). |
total_node_count |
number of unique node IDs present in results |
total_expr_count |
number of unique expressions present in results |
total_response_count |
number of unique responses seen |
node_seen |
list of those node IDs present in results |
expr_seen |
list of those expressions present in results |
node_expr_pairs_seen |
pairs of nodes and expressions present in results, including current status and average load |
Performance
OpenCache should be considered an experimental prototype, and is not built for production environments.
However, this is not to say that OpenCache performs poorly, rather it is not optimised for performance yet.
Currently, a cache instance is single-process but multi-threaded. Running alone on an 2.5GHz i5, one such instance can handle a maximum of ~650 requests per second (based on initial testing).
License
This software is licensed under the Apache License, Version 2.0.
Releases
OpenCache follows the Semantic Versioning System for numbering releases.
Author
OpenCache is developed and maintained by Matthew Broadbent (matt@matthewbroadbent.net). It can be found on GitHub at: http://github.com/broadbent/opencache.
