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distcache(8) |
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distcache − Distributed session caching
The distcache architecture provides a protocol and set of accompanying tools to allow applications, and indeed machines, to share session state between them by way of a network service.
The primary use of distcache right now is for SSL/TLS session caching. This allows SSL/TLS servers (eg. a secure Apache web server providing HTTPS support) to use a centralised session cache. This allows any server to resume any SSL/TLS sessions negotiated by another server on the network. The advantages to this approach include increased freedom on mechanisms for load-balancing − there is no need nor motivation to route incoming connections to the same server to improve the chances for SSL/TLS , and indeed doing so defeats the point of load−balancing, is a complex task requiring a lot of state, and the resulting routers can become a bottleneck and a single point of failure.
Future versions of distcache will expand on the protocol and should provide for a variety of "shared−state" uses besides SSL/TLS session caching.
dc_server
Runs a cache server listening on a configurable network address. See dc_server(1).
dc_client
Runs a local client proxy. This presents an interface to applications much like dc_server but itself manages multiplexing application requests to/from a cache server through a single persistent connection. See dc_client(1).
dc_test
Sends a (configurable) barrage of session caching requests to a given network address using the distcache protocol. Useful for testing correctness of an installation as well as benchmarking. See dc_test(1).
dc_snoop
A transparent proxy tool supporting the distcache protocol that can be used to monitor cache operation requests and responses between any two end-points (eg. between an application and dc_client, or between dc_client and dc_server). See dc_snoop(1).
The comments below provide a short summary of the APIs available in distcache. To view more details, consult the section 2 man pages these summaries refer to. If you are using a packaged version of distcache, you may need to ensure that a corresponding "devel" package is installed as the libraries, headers, and API documentation is often packaged independantly of the user tools.
libnal
This is the underlying Network Abstraction Library (hence " NAL ") used by the distcache libraries and tools. libnal uses non-blocking sockets, with an addressing abstraction that allows tools to transparently work over unix domain sockets or TCP/IPv4 sockets by a change of address text. For this reason, all the distcache tools can have their "−listen" and "−connect" switches set to work over either kind of transport.
libnal defines
various object types;
NAL_ADDRESS (see NAL_ADDRESS_new(2))
The addressing abstraction converts to and from text representations, indicates whether given addresses are valid for listening on, connecting to, or both.
NAL_CONNECTION (see NAL_CONNECTION_new(2))
This encapsulates a network connection that can be used for sending and receiving arbitrary binary data.
NAL_LISTENER (see NAL_LISTENER_new(2))
This encapsulates a listening socket that can be used to accept incoming connection requests on a configured address, creating a NAL_CONNECTION wrapper for each accepted connection.
NAL_SELECTOR (see NAL_SELECTOR_new(2))
This provides an object that can be prepared with various NAL_LISTENER and NAL_CONNECTION objects, and then can block waiting for network activity up to some configurable limit of time. This is the basis of non-blocking I/O and is an encapsulation of the traditional select(2) function.
NAL_BUFFER (see NAL_BUFFER_new(2))
This abstraction implements a FIFO data array and is used primarily for representing the read and send parts of a NAL_CONNECTION object.
There are also some helper functions to assist in serialising data, particularly with respect to putting integral data into network byte order (allowing interoperability between platforms with differing byte−order). These functions are documented in NAL_decode_uint32(2).
libdistcache
There are two
APIs implemented by the libdistcache library;
distcache/dc_plug.h
This header provides the DC_PLUG abstraction. This encapsulates a connection and implements the distcache protocol and various functions for manipulating the reading and writing of distcache messages (requests or responses). This abstraction can support client and server implementations of the distcache protocol and supports asynchronous behaviour by interacting with libnal’s NAL_SELECTOR type. For more information, see DC_PLUG_new(2).
distcache/dc_client.h
This header declares a higher-level (and much simpler) API than dc_plug.h, and is useful in applications that want API functions that ’’do cache operations’’. The API is blocking, and provides simplistic ’’add’’, ’’remove’’, and ’’get’’ functions that only return once the full request/response cycle is complete or an error has occured. This is the API used to add distcache support to applications like Apache, stunnel, etc. For more information, see DC_CTX_new(2).
libdistcacheserver
This header declares an API for implementing a session cache supporting the distcache protocol. It is primarily intended for environments that wish to implement an alternative method for session storage. As with elements of libdistcache, this API is likely to be undergoing some important restructuring and enhancements. Please consider subscribing to the distcache mail list and/or monitoring CVS , this gives you an opportunity to influence ongoing development and be less surprised at changes the turn up in future versions. For more information, see DC_SERVER_new(2).
The distcache toolkit, including the libnal network abstraction library that comes bundled with it, is distributed under the LGPL license ("Library GNU Public License") and you should have received a copy of this license with this software and its documents.
dc_server(1)
Distributed caching server.
dc_client(1)
Distributed caching client proxy
dc_snoop(1)
Distcache protocol analyser and debugging tool.
http://www.distcache.org/
Distcache home page.
This toolkit was designed and implemented by Geoff Thorpe for Cryptographic Appliances Incorporated. Since the project was released into open source, it has a home page and a project environment where development, mailing lists, and releases are organised. For problems with the software or this man page please check for new releases at the project web-site below, mail the users mailing list described there, or contact the author at geoff@geoffthorpe.net.
Home Page: http://www.distcache.org
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distcache(8) | |