Hosting Template Engine Server with Nginx and Openresty’s Lua Plugin

We wanted to have a server which can serve dynamically generated HTMLs from templates based on request. One can write this as a webapp in any web-framework and deploy on http server; but why not program the server itself!

The problem

We want server to return basic html from template. Something like whenever the http://localhost:8090/myapp?param1=hello&param2=John is called it should return text/html response which looks like this:

<html>
<body>
    <p>Nice to see you John. Platform greets you "hello".</p>
</body>
</html>

The name and greeting is compiled using a template from param. so the template looks like this:

<html>
<body>
    <p>Nice to see you {param1}. Platform greets you "{param2}".</p>
</body>
</html>

Nginx

Anyone working in web development would have heard about Nginx - most likely as the highly available server for setting up reverse proxy for load balancing. It can be used for many other services as well. Until recently I was using Nginx as just the server container with a simple config file which one can use to configure. After I met an Nginx module by Openresty for lua-nginx - I can use Nginx to program.

OpenResty turns the NGINX server into a powerful web app server, in which developers can use the Lua programming language to script various existing nginx C modules and Lua modules and construct extremely high-performance web applications that are capable to handle 10K ~ 1000K+ connections in a single box.

The solution

brew install openresty/brew/openresty
brew install pcre openssl curl

mkdir myapp
cd myapp

mkdir logs/ conf/ templates/ lua/

templates/greet.html

<html>
<body>
     <p>Nice to see you {param1}. Platform greets you "{param2}".</p>
</body>
</html>

installing lua’s templating library

One greatest benefit of using lua-nginx module would be able to use numerous existing libraries for programing our app. We would use lua-resty-template to compile the html templates. Installing library using OpenResty package manager (opm):

opm get bungle/lua-resty-template

lua/myapp.lua

local template = require("resty.template")
local template_string = ngx.location.capture("/templates/greet.html")
template.render(template_string.body, {
    param1 = ngx.req.get_uri_args()["param1"],
    param2 = ngx.req.get_uri_args()["param2"]
})

Bunch of things are used here. ngx is global variable we can use in our lua files to communicate with openresty’s nginx server.

conf/nginx.conf

worker_processes  1;
error_log logs/error.log;
events {
    worker_connections 1024;
}
http {
    root ./;
    server {
        listen 8090;

	    location /myapp {
		    default_type text/html;
		    content_by_lua_file ./lua/myapp.lua;
	    }
	}
}

run

./usr/local/openresty/nginx/sbin/nginx -p ~/myapp -c conf/nginx.conf

That should run the myapp server on 8090 port. And curl http://localhost:3000/myapp?param1=hello&param2=John should give the compiled HTML we wanted from our template.

TL;DR

Plain Nginx is fast and easy to configure. OpenResty gives enhanced support on Nginx; in a way it is Nginx++. This gives power to program Nginx with lua scripting - which is also fast and easy. One can make Nginx compile templates, do access validation, auth verification all in Nginx itself, even when configuring it as reverse proxy for a webapp.

References:

https://yos.io/2016/01/28/building-an-api-gateway-with-lua-and-nginx/
https://www.staticshin.com/top-tens/things-about-openresty.html
https://www.staticshin.com/programming/definitely-an-open-resty-guide/
https://openresty.org/en/installation.html
https://www.digitalocean.com/community/tutorials/how-to-use-the-openresty-web-framework-for-nginx-on-ubuntu-16-04
https://github.com/openresty/lua-nginx-module
https://github.com/bungle/lua-resty-template
https://stackoverflow.com/questions/19853930/getting-error-while-using-lua-with-nginx
https://github.com/bungle/awesome-resty