Zero downtime mechanism for software upgrade of a distributed computer system

A computerized method comprising:

• preparing a software patch update for upgrading one or more software components from a plurality of software components running on a plurality of application server nodes of a cluster;
• redirecting a plurality of service requests from a first instance of the cluster to a second instance of the cluster for execution, the plurality of service requests are executed by the plurality of software components;
• redirecting an execution in progress of a service request from the first instance of the cluster to the second instance of the cluster, the execution in progress proceeds from a state that is saved on a public store by the first instance of the cluster;
• and
• applying the software patch to the one or more software components running on an application server node of the first instance of the cluster.

An article of manufacture having computer readable instructions stored thereon for execution by a processor to perform a method, the method comprising:

• preparing a software patch update for upgrading one or more software components from a plurality of software components running on a plurality of application server nodes of a cluster;
• redirecting a plurality of service requests from a first instance of the cluster to a second instance of the cluster for execution, the plurality of service requests are executed by the plurality of software components;
• redirecting an execution in progress of a service request from the first instance of the cluster to the second instance of the cluster, the execution in progress proceeds from a state that is saved on a public store by the first instance of the cluster;
• and
• applying the software patch to the one or more software components running on an application server node of the first instance of the cluster.