apiserver seems to provide apis like: GET /api/v1/watch/nodes to watch and get nodes info. when controller-manager is working, how the watch api is called and where can i find this in source code?
You can watch changes by reading the api. If you want to use the supported go client you alternatively you could connect like this: https://github.com/kelseyhightower/motorboat/blob/master/main.go#L94