Linux-HA Phase I Requirements
                                       
   This document describes a set of general Linux-HA requirements which
   have been presented to the list, and no objections were made.  Of
   course, it would have been nice to have had a good discussion, but I
   take silence to mean assent :-)
   
Linux-HA Phase I General Goals

     * Simple
     * Reliable
     * Easy to configure
     * Easy to test
     * Easy to monitor
     * Redundant hardware and software are verified for working condition
       
Linux-HA Phase I Requirements

   The short-term goal of Phase I is to provide a more realistic
   demonstration of Linux-HA, in a form that will actually be usable to a
   certain set of customers (users) in a production sense.
   
   This demonstration is focused on providing High-Availability web
   service.  The rationale for providing web service is simple:  It is
   well-understood, and Linux has a significant presence in the web
   server market.  This will provide more initial users and testers than
   most other applications.
   
   The following minimal requirements on the web service are considered
   sufficient for this demonstration:
     * An active/standby methodology is acceptable.  Load sharing need
       not be explicitly supported
     * Data on standby nodes must be continually replicated from their
       paired active nodes over dedicated LANs.  I am referring
       specifically to application data, not cluster config data.
       
     * Comment: It is expected that we will use "poor man's replication"
       between the active and standby nodes
       
     IP address takeover between active and standby hosts. Ability to
   start and stop applications as IP addresses move around the cluster.
   
     Basic cluster monitoring capabilities via /proc-like interface
   
     Simple configuration and installation documentation
   
     Basic support for either resource groups or dependencies
   
Restrictions Allowed for Demonstration

   The following restrictions are considered acceptable for the
   demonstration.
     * It is not necessary to provide load sharing between members of the
       cluster (An active/standby methodology is acceptable)
     * A single active/standby pair is sufficient at the beginning
     * No application level notification of cluster transitions need be
       provided (though see the stop/start requirement above)
     * No hardware diagnostics need be provided
       
Post-Demonstration Requirement Candidates

   After these demonstration requirements have been met, it is expected
   that the following capabilities will be added (not listed in priority
   order):
     * Integration of hardware and software diagnostics into the
       architecture
     * Support for in-node IP interface failover (failing between NICs
       within a single host)
     * Application notification of cluster transitions (support for
       arbitrary application failover)
     * Plug-in modules interface available for cluster management
       
     * {allowing support for: active/standby, n+1, load sharing, etc.}
       
     Cluster management uses diagnostic information in failover strategy
   
     Arbitrary number of nodes in cluster.
   
     Multiple pairs of active/standby servers in the cluster
   
     Easily configured support for common servers like these: ftp, smtp,
   pop3, imap, DNS, others (?)
   This is intended to be something more sophisticated than changing run
   levels.  Changing run levels only supports the active/standby model.
   Note that these kinds of services may be started and stopped with
   /etc/rc.d/init.d scripts, but will not likely be tied to run levels.
   
     Load sharing between the active/replicator servers via NFS (?)
   
     Support for other replication configurations.  For example:
     * Shared SCSI
     * GFS
     * User-defined replication methods
       
     Sophisticated, cool GUI monitoring capabilities
   
     Cool GUI configuration tools
   
     Other cool and feasible things such as people are moved to do them
   :-)
   
     I have a bias against making the customer to write shell scripts to
   move resources around for "normal" cases.  This is in harmony with
   "easy to configure" and Cool GUI configuration tools.