Libraries and samples to deploy an OCaml application to an Nginx server - nginx

Question

I have developed a desktop application in OCaml under Ubuntu.
Now, I would like to deploy it to a DigitalOcean Ubuntu server (512 MB Memory / 20 GB Disk) that I own. I will use JavaScript programs on the client side to call the executable stored on the server side, then deal with the returned results.
However, I have no idea how to get started.
Someone pointed me to FastCGI, I did see some FastCGI settings in Nginx server. It seems that there are some OCaml libraries to handle FastCGI or CGI: ocamlnet, cgi, CamlGI, etc.
Could anyone tell me which library is stable and suits my need?
Besides, are there some samples of the library and the settings in Nginx server to let me get started?

Answer 1

I don't think the solution I will propose is the less heavy, but it has several advantages :
It allows you to generate the website in Ocaml, so that the interface with your code won't be to hard to do
If needed you will be able to export your whole application directly in Javascript : you won't let your serveur do useless computes that the user could do, and moreover you don't need to rewrite your code in Javascript, Ocsigen can convert your code for you
If some operations need to be performed by the serveur, you can really easily call server side functions from the client side code, and all your code will be written in Ocaml.
It's pretty easy
What is this amazing tool ? Ocsigen ! You can find a complete tutorial here.
Now let's see how you can use it
Install Ocsigen
First if you don't have it, install opam (it will allow you to install ocaml packages). Just follow the instructions on the website (I cannot paste link since I don't have enough reputation points), but basically for ubuntu run :
sudo add-apt-repository ppa:avsm/ppa
sudo apt-get update
sudo apt-get install ocaml ocaml-native-compilers camlp4-extra m4 opam
Then, you need to install Ocsigen. All instructions are here : https://ocsigen.org/install but basically just do :
sudo aptitude install libev-dev libgdbm-dev libncurses5-dev libpcre3-dev libssl-dev libsqlite3-dev libcairo-ocaml-dev m4 opam camlp4-extra
opam install eliom
(Note : you can also install it with apt-get if you don't want to install/use opam, but I prefer using opam to deal with ocaml depends, you can choose a precise version...)
Well it's done, you now have installed ocsigen !
Create the web page
Then to create a basic scaffold site just run
eliom-distillery -name mysite -template basic -target-directory mysite
and to run it :
cd mysite/
make test.byte
You should see a basic page at localhost:8080/.
Now, let's insert your code. Let's imagine it is named myscript and return a string :
let myscript () = "Here is my amazing result"
Add this code before the let () = in the file mysite.eliom, and add just after h2 [pcdata "Welcome from Eliom's distillery!"]; the line :
p [pcdata (Printf.sprintf "My script gives the return function : \"%s\"" (myscript ()))]
This will create a paragraphe (p) whose content (pcdata) contains the result of myscritpt.
For me the whole mysite.eliom gives :
{shared{
open Eliom_lib
open Eliom_content
open Html5.D
}}
module Mysite_app =
Eliom_registration.App (
struct
let application_name = "mysite"
end)
let main_service =
Eliom_service.App.service ~path:[] ~get_params:Eliom_parameter.unit ()
let myscript () = "Here is my amazing result"
let () =
Mysite_app.register
~service:main_service
(fun () () ->
Lwt.return
(Eliom_tools.F.html
~title:"mysite"
~css:[["css";"mysite.css"]]
Html5.F.(body [
h2 [pcdata "Welcome from Eliom's distillery!"];
p [pcdata (Printf.sprintf "My script gives the return function : \"%s\"" (myscript ()))]
])))
(Please note that let application_name = "mysite" must follow the name that you gave to eliom-distillery. If it's not the case your javascript won't be linked)
Let's compile again :
make test.byte
Now at localhost:8080 you can read :
My script gives the return function : "Here is my amazing result"
The result of the script has been included !
Going further
You can also define myscript to be run in client side, take some Post/Get param, or communicate with the page in real time in only a few lines, but if you want to learn more about that just read the ocsigen tutorial !
Interface with Nginx
I'm not sure you really need to interface it with Nginx, since ocsigenserver is supposed to run as an (http) serveur, but if needed you can always put ocsigenserver behing a Nginx serveur by using reverse-proxy (or the reverse thing, you can serve Nginx from ocsigenserver, read the ocsigenserver manual for more details).