[Xorp-hackers] process auto restart

[Pavlin Radoslavov]

> I have one question.  How is process auto restart addressed in XORP design?
> By process auto restart, I mean to automatically restart a process
> which exits abnormally, e.g. crash.
> 
> How can the restarted process get its configuration information? 

Ray,

The restarting can be done as follows:

 1. The rtrmgr detects that the process has exit abnormally by using
    one of the following mechanisms:
   (a) If the process is running on the same machine as the rtrmgr,
       then the rtrmgr can check the process' exit status after
       SIGCHLD.
   (b) The rtrmgr registers interest with the finder in that
       particular process' status. E.g., see the following XRL
       interfaces: finder_event_notifier/0.1 and
       finder_event_observer/0.1 (inside files
       xrl/interfaces/finder_event_notifier.xif and
       xrl/interfaces/finder_event_observer.xif).

 2. Once the abnormal exit is detected, the rtrmgr can check its
    current configuration related to this particular process, and
    will execute only those tasks that are needed to start the
    process and configure it. Those tasks include the particular
    command to start the process, and the XRLs to configure it
    (remember that all configuration is done via XRLs sent by the
    rtrmgr to the process).

In other words, the rtrmgr has all the responsibility for restarting
and configuring the process, and the process itself does not need to
do anything special.

Note that currently the rtrmgr only detects (using 1(a)) that a
process has exit abnormally, but it does not attempt to restart it.
The restarting should be added in one of the future releases.

Regards,
Pavlin