In Service Software Upgrade support for high availability for performing zero downtime upgrade

During a regular upgrade process in a high availability setup, at some point, both nodes run different software builds. These two builds can have the same or different internal high availability version numbers.

If both the builds have different high availability version numbers, connection failover (even if it is enabled) for existing data connections is not supported. In other words, all existing data connections are lost, which leads to downtime.

To address this issue, in Service Software Upgrade (ISSU) can be used for high availability set-ups. ISSU introduces a migration functionality, which replaces the force failover operation step in the upgrade process. The migration functionality takes care of honoring the existing connections and includes the force failover operation.

After migration operation is performed, the new primary node always receives traffic (request and response) related to the existing connections but steers them to the old primary node. The old primary node processes the data traffic and then sends them directly to the destination.

How the enhanced ISSU works

The regular upgrade process in a high availability setup consist of the following sequential steps:

  1. Upgrade the secondary node. This step includes software upgrade of the secondary node and restart of the node.

  2. Force Failover. Running the force failover makes the upgraded secondary node to primary, and the primary node to secondary.

  3. Upgrade the new secondary node. This step includes software upgrade of the new secondary node and restart of the node.

During the time frame between step 1 and step 3, both nodes run different software builds. These two builds can have the same or different internal high availability versions.

If both the builds have different high availability version numbers, connection failover (even if it is enabled) for existing data connections not supported. In other words, all existing data connections are lost, which leads to downtime.

The ISSU upgrade process in a high availability setup consists of the following steps:

  1. Upgrade the secondary node. This step includes software upgrade of the secondary node and restart of the node.

  2. ISSU migration operation. The step includes the force failover operation and takes care of the existing connections. After you perform the migration operation, the new primary node always receives traffic (request and response) related to the existing connections but steers them to the old primary node through the configured SYNC VLAN in GRE tunnel. The old primary node processes the data traffic and then sends them directly to the destination.

  3. Upgrade the new secondary node. This step includes software upgrade of the new secondary node and restart of the node.

Before you begin

Before you start performing the ISSU process in a high availability setup, go through the following pre-requisites and limitations:

  • Make sure the SYNC VLAN is configured on both the nodes of the high availability setup. For more information, see Restricting high availability synchronization traffic to a VLAN.
  • ISSU is not supported in Microsoft Azure cloud because Microsoft Azure does not support GRE tunneling.
  • High availability config propagation and synchronization do not work during ISSU.
  • ISSU is not supported for IPv6 high availability setup.
  • ISSU is not supported for following sessions:
    • IPv6
    • Jumbo frames
    • IPv6 sessions
    • Large scale NAT (LSN)

Configuration steps

ISSU includes a migration feature, which replaces the force failover operation in the regular upgrade process of a high availability setup. The migration functionality takes care of honoring the existing connections and includes the force failover operation.

During the ISSU process of a high availability setup, you run the migration operation just after you upgraded the secondary node. You can perform the migration operation from either of the two nodes.

CLI Procedure

To perform the high availability migration operation by using the CLI:

At the command prompt type:

migrate ns

GUI Procedure

To perform the high availability migration operation by using the GUI:

Navigate to System, click System Information tab, and then click Migrate.

In Service Software Upgrade support for high availability for performing zero downtime upgrade