# Load balancer for Tangle accelerator (using Nginx)

## Introduction
The ngx_http_upstream_module module is used to define groups of servers that can be referenced by the proxy_pass, fastcgi_pass, uwsgi_pass, scgi_pass, memcached_pass, and grpc_pass directives.

## Example Configuration
* Directives
* weight
* The default weight is 1
* Weight 2 will be sent twice as much traffic as weight 1

upstream backend {
    server backend1.example.com       weight=5;
    server backend2.example.com:8080;
    server unix:/tmp/backend3;

    server backup1.example.com:8080   backup;
    server backup2.example.com:8080   backup;
}

server {
    location / {
        proxy_pass http://backend;
    }
}

## Limitation
* Health check
* Not active
* If an error occurs during communication with a server, the request will be passed to the next server, and so on until all of the functioning servers will be tried. If a successful response could not be obtained from any of the servers, the client will receive the result of the communication with the last server.

* Plus version
* Active Health Checks

## Load balancer demo site
* DEVNET
* http://node0.puyuma.org:8000

## Upstream backend
* DEVNET
* node2.puyuma.org:8000
* node3.puyuma.org:8000
* node4.puyuma.org:8000
* node5.puyuma.org:8000
* node6.puyuma.org:8000
* node0.puyuma.org:8001
* node10.puyuma.org:8001
* node.deviceproof.org:8000

## Service file

#### Nginx configuration
* /etc/nginx/conf.d/load_balancer.conf

log_format upstreamlog '[$time_local] $remote_addr - $remote_user - $server_name  to: $upstream_addr: $request upstream_response_time $upstream_response_time msec $msec request_time $request_time';

access_log /var/log/nginx/load_balancer.log upstreamlog buffer=32k;

* Log format

[06/Sep/2018:15:24:40 +0800] 220.134.55.99 - - - _  to: 140.131.178.244:8000, 140.116.82.61:8001: GET / HTTP/1.1 upstream_response_time 3.011, 0.003 msec 1536218680.481 request_time 3.014
[06/Sep/2018:15:24:40 +0800] 220.134.55.99 - - - _  to: 140.116.245.161:8001: GET /favicon.ico HTTP/1.1 upstream_response_time 0.002 msec 1536218680.955 request_time 0.002
[06/Sep/2018:15:24:42 +0800] 220.134.55.99 - - - _  to: 140.116.82.61:8001: GET / HTTP/1.1 upstream_response_time 0.002 msec 1536218682.078 request_time 0.002
[06/Sep/2018:15:24:42 +0800] 220.134.55.99 - - - _  to: 140.116.245.161:8001: GET /favicon.ico HTTP/1.1 upstream_response_time 0.002 msec 1536218682.234 request_time 0.002
[06/Sep/2018:15:25:01 +0800] 220.134.55.99 - - - _  to: 140.116.82.61:8001: GET / HTTP/1.1 upstream_response_time 0.002 msec 1536218701.725 request_time 0.002
[06/Sep/2018:15:25:01 +0800] 220.134.55.99 - - - _  to: 140.116.245.161:8001: GET /favicon.ico HTTP/1.1 upstream_response_time 0.002 msec 1536218701.890 request_time 0.002
[06/Sep/2018:15:25:01 +0800] 220.134.55.99 - - - _  to: 140.116.82.61:8001: GET / HTTP/1.1 upstream_response_time 0.001 msec 1536218701.905 request_time 0.001
[06/Sep/2018:15:25:02 +0800] 220.134.55.99 - - - _  to: 140.116.245.161:8001: GET /favicon.ico HTTP/1.1 upstream_response_time 0.002 msec 1536218702.079 request_time 0.002
[06/Sep/2018:15:25:05 +0800] 220.134.55.99 - - - _  to: 140.131.178.244:8000, 140.116.82.61:8001: GET / HTTP/1.1 upstream_response_time 3.011, 0.003 msec 1536218705.101 request_time 3.014
[06/Sep/2018:15:25:05 +0800] 220.134.55.99 - - - _  to: 140.116.245.161:8001: GET /favicon.ico HTTP/1.1 upstream_response_time 0.002 msec 1536218705.549 request_time 0.002

## Reference
* [Module ngx_http_upstream_module](http://nginx.org/en/docs/http/ngx_http_upstream_module.html)
* [Nginx Compare versions](https://www.nginx.com/products/nginx/#compare-versions)
* [ How To Set Up Nginx Load Balancing
](https://www.digitalocean.com/community/tutorials/how-to-set-up-nginx-load-balancing)

## TODO

* Install Nginx `ngx_http_log_module` module to record the reverse proxy upstream server serving
* [how-to-record-reverse-proxy-upstream-server-serving-request-in-nginx-log](https://stackoverflow.com/questions/18627469/how-to-record-reverse-proxy-upstream-server-serving-request-in-nginx-log)
* [Nginx Module ngx_http_log_module](http://nginx.org/en/docs/http/ngx_http_log_module.html)
* Auth2 support
* https://github.com/jirutka/ngx-oauth