A Shirako deployment runs as a dynamic collection of interacting peers that work together to coordinate asynchronous actions on the underlying resources. Each actor is a multithreaded server written in Java and running within a Java Virtual Machine. Actors communicate using an asynchronous peer-to-peer messaging model through a replaceable stub layer. SOAP stubs allow actors running in different JVMs to interact using Web Services protocols (Apache Axis).
Our goal was to build a common toolkit for all actors that is understandable and maintainable by one person. Table 2 shows the number of lines of Java code (semicolon lines) in the major system components of our prototype. In addition, there is a smaller body of code, definitions, and stubs to instantiate groups of Shirako actors from XML descriptors, encode and decode actor exchanges using SOAP messaging, and sign and validate SHARP-compliant exchanges. Shirako also includes a few dozen Ant scripts, averaging about 40 lines each, and other supporting scripts. These scripts configure the various resources and applications that we have experimented with, including those described in Section 5. Finally, the system includes a basic Web interface for Shirako/COD actors; it is implemented in about 2400 lines of Velocity scripting code that invokes Java methods directly.
The prototype makes use of several other open-source components. It uses Java-based tools to interact with resources when possible, in part because Java exception handling is a basis for error detection, reporting, attribution, and logging of configuration actions. Ant tasks and the Ant interpreter are written in Java, so the COD resource drivers execute configuration scripts by invoking the Ant interpreter directly within the same JVM. The event handlers often connect to nodes using key-based logins through jsch, a Java secure channel interface (SSH2). Actors optionally use jldap to interface to external LDAP repositories for recovery. COD employs several open-source components for network management based on LDAP directory servers (RFC 2307 schema standard) as described below.