Attachment 179501 Details for Bug 247772 – Preliminary event parser specification.

Preliminary event parser specification.

specs.txt (text/plain), 4.36 KB, created by Lon Hohberger on 2007-08-29 18:04:53 UTC

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Creator: Lon Hohberger

Created: 2007-08-29 18:04:53 UTC

Size: 4.36 KB

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obsolete

>Basic configuration specification:
>
>  <rm>
>    <events>
>      <event class="node"/>        
>      <event class="node"
>             node_name="bar"/>     
>      <event class="node"
>             node_name="foo"
>             node_state="up"/>     
>      <event class="node"
>             node_id="3"
>             node_state="down"/>   
>
>          (note, all service ops and such deal with node ID, not
>           with node names)
>
>      <event class="service"/>     
>      <event class="service"
>             service_name="A"/>    
>      <event class="service"
>             service_name="B"
>         service_state="started"/> 
>    </event>
>    ...
>  </rm>
>
>Node event globals:
>  
>   n_name - node name
>   n_id - node ID
>   n_state - new node state
>
>Service event globals:
>
>   svc_name
>   svc_state
>   svc_owner (ID... if running; <= 0 if not)
>
>C-binding functions:
>
>  service_owner( servicename )  <-- returns node ID (int)
>
>  service_status( servicename ) <-- returns string
>
>  service_count( nodeID )       <-- returns # of services on the node
>
>  node_state( nodeID )          <-- returns node state
>
>  service_start(s, pref_nodeID, avoid_nodeID)
>                                <-- start a not-running service on
>                                    preferred node.  In any case, avoid
>                                    the avoid node.
>
>  service_relocate(s, pref_nodeID, avoid_nodeID)
>                                <-- relo. a running service to the
>                                    preferred node.  In any case, avoid
>                                    the avoid node.  (both node specs
>                                    are optional)
>  service_stop(s)               <-- stop the service
>  service_fail(s)               <-- fail the service
>  service_disable(s)            <-- disable the service (note: you can
>                                    NOT disable a failed service from
>                                    an event script; you must do this
>                                    manually))
>
>  ...
>
>I prototyped a simplistic script language which should work (using
>lex/yacc).  I also started (barely) on the internal executive for it,
>which would be fairly efficient since it's a very limited language.
>However, it would still take awhile to get it fully put together.
>
>So, I also grabbed Lua (an embedded script language) and was able to
>create a C-bound function in about 45 minutes, build a test program, and
>call a test lua-script which called the c-bound function.  We don't ship
>Lua in RHEL, so either we'd have to provide it as a library in rgmanager
>or embed it statically in rgmanager if we were to use it.
>
>If we use Lua, it'll take maybe a week (mostly writing binding
>functions) to develop functions to let admins do (literally) whatever
>they need on events.  Probably double if I finish the internal (more
>simplistic, but faster and smaller) parser.  As a side note, doing the
>latter has the side effect of being able to rewrite the front-end so
>long as the intermediate tree is built correctly - that is, once I get
>the back end done, the front-end can be reworked and be entirely done
>using XML for example.
>
>So, with either language construct, it's reasonably easy to do something
>like this in cluster.conf:
>
><event class="node" node_state="down">
>    if service_owner("service:SAP_main") == n_id) and
>       service_state("service:SAP_main") == "started") then
>
>        -- fail over service if it was running to the node running
>        -- the service named "SAP_replicated"
>		start_service("service:SAP_main",
>			service_owner("service:SAP_replicated"), 0))
>	end
></event>
>
>Move SAP replication server away from the SAP main if they're cohabiting
>and/or start the initial instance of the replication server on cluster
>boot:
>
><event class="service" name="service:SAP_main" state="started">
>	if service_state("service:SAP_replicated") == "disabled" then
>		start_service("service:SAP_replicated", ...)
>    else if service_owner("service:SAP_main") == 
>	   service_owner("service:SAP_replicated") then
>		relocate_service("service:SAP_repicated", ...)
>	end
></event>
>
>Note that I am also exploring the ability to use a parsed XML tree as
>a programming construct (like XEXPR, but with the ability to register
>functions...).

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