In Service System Upgrade - ISSU

Use ISSU to upgrade and troubleshoot an active switch with minimal disruption to the network.

ISSU includes the following modes:

• Restart
• Upgrade
• Maintenance

Restart Mode

You can configure the switch to restart in one of the following modes.

• cold restarts the system and resets all the hardware devices on the switch (including the switching ASIC).

• fast restarts the system more efficiently with minimal impact to traffic by reloading the kernel and software stack without a hard reset of the hardware. During a fast restart, the system decouples from the network to the extent possible using existing protocol extensions before recovering to the operational mode of the system. The restart process maintains the forwarding entries of the switching ASIC and the data plane is not affected. Traffic outage is much lower in this mode as there is a momentary interruption after reboot, while the system reinitializes.

• warm restarts the system with no interruption to traffic for existing route entries. Warm mode diverts traffic from itself and restarts the system without a hardware reset of the switch ASIC. While this process does not affect the data plane, the control plane is absent during restart and is unable to process routing updates. However, if no alternate paths exist, the switch continues forwarding with the existing entries with no interruptions.

  When you restart the switch in warm mode, BGP only performs a graceful restart if the BGP graceful restart option is set to full. To set BGP graceful restart to full, run the nv set router bgp graceful-restart mode full command, then apply the configuration with nv config apply. For more information about BGP graceful restart, refer to Optional BGP Configuration.

NVIDIA recommends you use NVUE commands to configure restart mode and reboot the system. If you prefer to use csmgrctl commands, you must stop NVUE from managing the /etc/cumulus/csmgrd.conf file before you set restart mode:

1. Run the following NVUE commands:

   cumulus@switch:~$ nv set system config apply ignore /etc/cumulus/csmgrd.conf
   cumulus@switch:~$ nv config apply
   

2. Edit the /etc/cumulus/csmgrd.conf file and set the csmgrctl_override option to true:

   cumulus@switch:~$ sudo nano /etc/cumulus/csmgrd.conf
   csmgrctl_override=true
   ...
   

3. Save the configuration:

   cumulus@switch:~$ nv config save
   

The following command configures the switch to restart in cold mode:

cumulus@switch:~$ nv set system reboot mode cold
cumulus@switch:~$ nv config apply

cumulus@switch:~$ sudo csmgrctl -c

The following command configures the switch to restart in fast mode:

cumulus@switch:~$ nv set system reboot mode fast
cumulus@switch:~$ nv config apply

cumulus@switch:~$ sudo csmgrctl -f

The following command configures the switch to restart in warm mode.

cumulus@switch:~$ nv set system reboot mode warm
cumulus@switch:~$ nv config apply

cumulus@switch:~$ sudo csmgrctl -w

To reboot the switch in the restart mode you configure above with NVUE:

cumulus@switch:~$ nv action reboot system no-confirm

To show system reboot information, such as the reboot date and time, reason, and reset mode (fast, cold, warm), run the NVUE nv show system reboot command:

cumulus@switch:~$ nv show system reboot
           operational                       applied  pending
---------  --------------------------------  -------  -------
reason                                                       
  gentime  2023-04-26T15:11:23.140569+00:00                  
  reason   Unknown                                           
  user     system/root

Upgrade Mode

Upgrade mode updates all the components and services on the switch to the latest Cumulus Linux minor release without impacting traffic. After upgrade is complete, you must restart the switch with either a warm, cold, or fast restart.

If the switch is in warm restart mode, restarting the switch after an upgrade does not result in traffic loss (this is a hitless upgrade).

Upgrade mode includes the following options:

• all runs apt-get upgrade to upgrade all the system components to the latest release without affecting traffic flow. You must restart the system after the upgrade completes with one of the restart modes.
• dry-run provides information on the components you want to upgrade.

The following command upgrades all the system components:

cumulus@switch:~$ sudo csmgrctl -u

The following command provides information on the components you want to upgrade:

cumulus@switch:~$ sudo csmgrctl -d

Maintenance Mode

Maintenance mode isolates the system from the rest of the network so that you can perform intrusive troubleshooting tasks and data collection or perform system changes, such as break out ports and replace optics or cables with minimal disruption.

Enable Maintenance Mode

Run the following command to enable maintenance mode. When maintenance mode is on, ISSU performs a graceful BGP shutdown, redirects traffic over the peerlink and brings down the MLAG port link. switchd maintains full capability.

cumulus@switch:~$ sudo csmgrctl -m1

You can run additional commands to bring all the ports down, then up to restore the port admin state.

cumulus@switch:~$ sudo csmgrctl -p0
cumulus@switch:~$ sudo csmgrctl -p1

Disable Maintenance Mode

Run the following command to disable maintenance mode and restore normal operation. When maintenance mode is off, ISSU performs a soft restart, runs a BGP graceful restart, and brings the MLAG port link back up. switchd maintains full capability.

cumulus@switch:~$ sudo csmgrctl -m0

Show Maintenance Mode Status

To see the status of maintenance mode, run the Linux sudo csmgrctl -s command. For example:

cumulus@switch:~$ sudo csmgrctl -s
Current System Mode: Maintenance since Tue Jan  5 00:13:37 2021 (Duration: 00:00:31)
 Boot Mode: reboot_cold  
 2 registered modules
 frr     : Maintenance, down
 switchd : Maintenance, down