Concurrency

Resources are converged one after the other, in the order of the program. Creating a server takes a while; when resources do not depend on each other, converge them at the same time with concurrently:

(define-values (key ip data)
  (concurrently
   (hetzner-ssh-key "me" #:public-key-file "~/.ssh/id_ed25519.pub")
   (hetzner-primary-ip "forge" #:location "fsn1")
   (hetzner-volume "data" #:size 10 #:location "fsn1")))

Each expression runs in its own thread, and concurrently returns their values in order.

If one fails, the others finish, then the error is raised, and the stage deletes nothing.

call-concurrently does the same with procedures, for a list built at run time:

(apply call-concurrently
       (map (lambda (name)
              (lambda ()
                (hetzner-server name #:type "cx23" #:location "fsn1")))
            '("web-1" "web-2" "web-3")))