Process Restartability; Enabling Process Restartability - Dell S4820T Configuration Manual

Process Restartability

Process restartability is an extension to the Dell Networking OS high availability system component that
enables application processes and system protocol tasks to be restarted.
This extension increases system reliability and uptime by attempting to restart the crashed process on
primary RPM before executing the failover procedure as a last resort.
Currently, if a software exception occurs, Dell Networking OS executes a failover procedure. In a single-
RPM system, the system generates a coredump and reboots; in a dual-RPM system, the system generates
a coredump and fails over to the standby RPM.
With a system reload, the system must read and apply the entire startup-config file, which might take
some time if the startup-config is large. Restarting a process saves time because only a portion of the
configuration related to the crashed process is read and reapplied.
For a dual-RPMs system, restarting a process also precludes launching the failover process on the
primary and standby RPMs. Recovery is attempted first locally on the primary RPM, which involves less
CPU overhead, increasing the systems availability for other activities.
However, in both single and dual-RPM systems, even when you configure process restart, the coredump
portion of failover is still executed.
The processes that you can restart fall under three categories:
• Interface-related processes — TACACS+, RADIUS, CLI, and SSH, and so on.
• Protocol tasks — OSPF, RIP, and ACL, and so on. Process restart is not currently available for protocol
tasks; the failover procedure is executed immediately after software exception.
• Line card processes — IPC, Event Log Agent, Line Card Manager, and so on. Process restart is not
currently available for line card processes; the failover procedure is executed immediately after
software exception.

Enabling Process Restartability

The restart time varies by process.
In general, interface-related processes are hitless and can be restarted in seconds; if a restart is
successful, traffic is not interrupted. Protocol tasks and line card processes are not hitless and take longer
to restart. You can select which process may attempt to restart and the number of consecutive restart
attempts before failover, but by default, every process fails over.
• Enable process restartability for a process or task.
CONFIGURATION mode
process restartable [process] [try number] [timestamp hours]
• Display the processes and tasks configured for restart.
EXEC Privilege
When a process restarts, FTOS displays a message similar to the following message.
[9/18 23:22:21] TME-(tme): Starting to restart the failed process tacplus
[9/18 23:22:41] TME-(tme): Finishing restarting the failed process tacplus
You can specify the timestamp in hour(s) so that if the number of attempts to restart exceeds the
maximum allowed within this timestamp, Restart mode is changed into Failover mode from that moment
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High Availability (HA)