NGINX - OpenResty - How to reverse proxy a call to 2 different servers based based on a string?

Question

I'm trying to configure NGINX/OpenResty to proxy SOAP calls to 2 different servers based on a string present on the SOAP request.

What I'm able to do: I am able to proxy requests to 2 different servers based on the path the SOAP client is calling:

location /pathA { proxy_pass http://www.ServerA.com/PathA/; } location /pathB { proxy_pass http://www.ServerB.com/PathB/; } 

What I can't do:

I can't separate the traffic based on the content of the request. The main reason I believe is that I can't correctly assemble the LUA script to extract the information and later use it to proxy the request.

location / { conten_by_lua ' ngx.req.read_body() local match = ngx.re.match(ngx.var.request_body,"STRING TO FIND") if match then proxy_pass http://www.ServerA.com/PathA/; else proxy_pass http://www.ServerB.com/PathB/; 

how can I achieve this?

I installed OpenResty and LUA is working fine.

I think I read somewhere that if the request is not an HTTP POST ngx.req.read_body() would not work. Is that correct?

Thank you for your help.

Answer 1

You almost did it youself, the only thing I would do differently is to use rewrite_by_lua instead of content_by_lua:

location / { set $proxy ""; rewrite_by_lua ' ngx.req.read_body() local match = ngx.re.match(ngx.var.request_body, "STRING TO FIND") if match then ngx.var.proxy = "www.ServerA.com" else ngx.var.proxy = "www.ServerB.com" end '; proxy_pass http://$proxy$uri; } 

If request is not an HTTP POST or has an empty body, ngx.req.read_body() will return nil, so it is better to add an additional check:

location / { set $proxy ""; rewrite_by_lua ' ngx.req.read_body() local body = ngx.var.request_body if (body) then local match = ngx.re.match(body, "STRING TO FIND") if match then ngx.var.proxy = "www.ServerA.com" else ngx.var.proxy = "www.ServerB.com" end else ngx.status = ngx.HTTP_NOT_FOUND ngx.exit(ngx.status) end '; proxy_pass http://$proxy$uri; } 

You also can limit allowed methods:

location / { limit_except POST { deny all; } ... } 

One more thing. With this configuration, if you specify your backends with domain names instead of IP addresses, you'll need a resolver directive in your config. You can use your local name server if you have one, or use something external like Google public DNS (8.8.8.8) or DNS provided for you by your ISP.

Answer 2

Here is the code snippets I used in openresty to distinguish dev and prod webhook according to posted json body:

server { listen 8080; resolver 114.114.114.114 8.8.8.8 valid=30s; location /webhook { limit_except POST { deny all; } set $proxy ""; rewrite_by_lua_block { local devWebhook = "myservice.dev" -- todo local prodWebhook = "mysevice.prod" -- todo function getFile(file_name) local f = assert(io.open(file_name, 'r')) local string = f:read("*all") f:close() return string end ngx.req.read_body() local data = ngx.req.get_body_data() if nil == data then local file_name = ngx.req.get_body_file() if file_name then data = getFile(file_name) end end local json = require("cjson.safe") local t = json.decode(data) if not (type(t) == "table" and t["msg"]) then ngx.exit(400) end local msg = ngx.unescape_uri(t["msg"]) if not (type(msg) == "string" and #msg > 0) then ngx.exit(400) end if string.find(msg, '"title":".*test product.*"') then ngx.var.proxy = devWebhook else ngx.var.proxy = prodWebhook end } proxy_pass http://$proxy$uri; } }