Methods for improving reliability while upgrading software programs in a clustered computer system

A method for upgrading a software program from a first version to a second version, said software program being implemented as software modules running on a plurality of computers coupled in a cluster configuration in a clustered computer system, said method comprising:

• replacing a subset of said software modules with said second version of said software program;
• assigning said subset of software modules with a first certification level;
• monitoring performance of said subset of software modules to ascertain whether said subset of software modules meet a predefined reliability criteria after said replacing;
• if said subset of software modules meet said predefined reliability criteria, designating said subset of software modules with a second certification level, wherein said subset of software modules receive transaction requests that require said software program at a first rate when assigned said first certification level, said subset of software modules receive said transaction requests that require said software program at a second rate when assigned said second certification level, said second certification level being higher than said first certification level;
• wherein said replacing said subset of said software modules replaces said subset of said software modules with said second version of said software program on a first subset of said plurality of computers of said clusters while a second subset of computers of said cluster maintains said first version of said software program, further comprising sharing a work load of said transaction requests for said software program in a clustering relationship between said plurality of computers, wherein said sharing routes a first subset of said transaction requests to said first subset of said plurality of computers so that said subset of software modules does not receive transaction requests above said first rate and routes a second subset of said transaction requests to said second subset of said plurality of computers.