[racket] racket distributed hello-world example error

i run the hello-world example in distributed-lib but got a socket error.

here is what i did:
1, i  have a pc and a VPS
2, i  can login the VPS from the pc  without password. (ssh)
3, they both running racket6.1
4,i  change localhost to the ip of the vps in  hello-world.rkt
        
then i run hello-word.rkt but it block then got a socket error.

in fact,i do not know how racket distributd work,but what else should i do to make it run correct.