Nginx-lua Dynamic location to upstream

[Simone]

Hi there,
I've Just started to play with Lua and this is what I'd like to achieve:
I expose a location and a lua script Will inspect http args.Once It takes the args,It Will call an external api searching for a specific content and It Will writes the returned json values on some lua variables.
Based on the returned values,Nginx Will proxy_pass to the right upstream.
Does Nginx/luajit cache all json values/pages based on different calls?I don't really want to call an external api for every single location request...
Thanks a lot.

[Martin Gee]

You'll need your own cache.  https://github.com/sourcelair/ceryx  is a project that does a lot of what you're looking for. You can read the code to see how it's using ShareMemory as a cache for routes. 

[Rob Kay]

If you make the request to the external API using ngx.location.capture() via a proxy pass, you can configure the proxy pass to use nginx native caching. Something like:

http {

    proxy_cache_path /path/to/cache keys_zone=my_cache:100m;

}

upstream external_api {

    server external.api.com:443;

}

upstream backend1 {

    server 1.1.1.1:443;

}

upstream backend2 {

    server 2.2.2.2:443;

}

location / {

    set $chosen_backend '';

    set $reqeust_uri '';

    access_by_lua_block {

        local json = require 'cjson'

        local lua_request_uri = '/api/v1/searchterm' .. ngx.var.arg_searchterm

        api_response = ngx.location.capture('/external_api', {

            vars = {

                request_uri = lua_request_uri

            }

        })

        response_json = json.decode(api_response)

        if response_json['result'] then

            ngx.var.chosen_backend = 'backend1' 

        else

            ngx.var.chosen_backend = 'backend2'

        end

    }

    proxy_pass https://$chosen_backend;

}

location /external_api {

    internal;

    proxy_pass https://external_api/$api_request;

    proxy_cache my_cache;

    proxy_cache_key $uri;

    proxy_cache_valid 200 5m;

}

[David Birdsong]

What are your route/upstream invalidation requirements?

If it's reasonable to fit in memory, just do the lookups in an access_by_lua* or rewrite_by_lua* block and cache the values in a lua module. If you can live w/ simply expiring out the info on a small interval, use the lua shared memory with whatever expiry is appropriate. 

...and then in increasing levels of sophistication:

https://github.com/openresty/srcache-nginx-module

https://github.com/pintsized/ledge

If you can't preset your upstream servers in the config, use balancer_by_lua to allow for your backends to be defined on the fly. Your code can access in data you've retrieved in the access_by or rewrite_by phases.

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