Maintaining client version affinity during a rolling server cluster upgrade includes a server in the server cluster receiving a request from a client and checking the request for a version cookie indicating a software version that the client is running. Responsive to a determination that the server is running the same software version as the client, the server serves the request. Responsive to a determination that the client is running a software version matching a previous software version of the server, the server initiates a software upgrade on the client instead of servicing the request. Responsive to a determination that the server is not running the same software version as the client, the server forwards the request to one of the other servers in the server cluster that is running the same software version as the client.