1. An application upgrade method, comprising: receiving an application deployment request, wherein the application deployment request comprises a deployment package of a to-be-deployed application, wherein the deployment package of the to-be-deployed application describes a node template of the to-be-deployed application, an identifier of a deployed application, an identifier of a node template of the deployed application, an identifier of a first platform node template, a version requirement of the node template of the to-be-deployed application for the first platform node template, and an upgrade identifier indicating that the node template of the to-be-deployed application is used to upgrade the node template of the deployed application indicated by the identifier of the node template of the deployed application; determining, according to the upgrade identifier, that the deployment package of the to-be-deployed application is an upgrade package of the deployed application indicated by the identifier of the deployed application; acquiring, according to the identifier of the deployed application, an identifier that is of a first platform node and corresponding to the identifier of the first platform node template, and acquiring a version of the first platform node indicated by the identifier of the first platform node; determining, according to the version of the first platform node, that the version of the first platform node is below the version requirement of the node template of the to-be-deployed application for the first platform node template; acquiring, according to the version requirement of the node template of the to-be-deployed application for the first platform node template, a first platform node upgrade package that meets the version requirement of the node template of the to-be-deployed application for the first platform node template; upgrading the first platform node indicated by the identifier of the first platform node by using the first platform node upgrade package; determining an identifier of a to-be-upgraded application node; and upgrading the application node indicated by the identifier of the to-be-upgraded application node by using the deployment package of the to-be-deployed application.