nginx lua balancer example

config.lua

return {
  servers = {
    foo = {'127.0.0.1', 9001},
    bar = {'127.0.0.1', 9002},
    baz = {'127.0.0.1', 9003},
  }
}

nginx.bar.conf

daemon off;
worker_processes 1;
pid nginx.bar.pid;
error_log stderr debug;

events {
  worker_connections 1024;
}

stream {

  lua_code_cache off;

  init_by_lua_block {
    require('ngx.balancer')
    require('server')
    require('config')
  }

  server {
    listen 9002;
    proxy_pass dispatcher;
    preread_by_lua_block {
      require('server').serve('bar')
    }
  }

  upstream dispatcher {
    server 0.0.0.1:1234;
    balancer_by_lua_block {
      require('server').dispatch()
    }
  }

}

nginx.baz.conf

daemon off;
worker_processes 1;
pid nginx.baz.pid;
error_log stderr debug;

events {
  worker_connections 1024;
}

stream {

  lua_code_cache off;

  init_by_lua_block {
    require('ngx.balancer')
    require('server')
    require('config')
  }

  server {
    listen 9003;
    proxy_pass dispatcher;
    preread_by_lua_block {
      require('server').serve('baz')
    }
  }

  upstream dispatcher {
    server 0.0.0.1:1234;
    balancer_by_lua_block {
      require('server').dispatch()
    }
  }

}

nginx.foo.conf

daemon off;
worker_processes 1;
pid nginx.foo.pid;
error_log stderr debug;

events {
  worker_connections 1024;
}

stream {

  lua_code_cache off;

  init_by_lua_block {
    require('ngx.balancer')
    require('server')
    require('config')
  }

  server {
    listen 9001;
    proxy_pass dispatcher;
    preread_by_lua_block {
      require('server').serve('foo')
    }
  }

  upstream dispatcher {
    server 0.0.0.1:1234;
    balancer_by_lua_block {
      require('server').dispatch()
    }
  }

}

server.lua

local balancer = require('ngx.balancer')

local config = require('config')
local servers = config.servers


local _M = {}


local answer = function(own_id, ...)
  ngx.say('[', own_id, '] ', ...)
end


local log_err = function(...)
  args = {...}
  table.insert(args, '\n\n')
  ngx.log(ngx.ERR, '\n\n*** ', table.unpack(args))
end


_M.serve = function(own_id)
  answer(own_id, 'connected')
  local sock = ngx.req.socket()
  while true do
    local data, err = sock:receive('*l')
    if not data then
      log_err('read error: ', err)
      ngx.exit(ngx.ERROR)
    end
    if data:sub(1, 1) == '/' then
      local upstream_id = data:sub(2)
      answer(own_id, 'connecting to upstream: ', upstream_id)
      ngx.ctx.upstream_id = upstream_id
      ngx.exit(ngx.OK)
    else
      answer(own_id, 'echo: ', data)
    end
  end
end


_M.dispatch = function()
  local upstream_id = ngx.ctx.upstream_id
  local upstream = servers[upstream_id]
  if not upstream then
    log_err('unknown upstream: ', upstream_id)
    ngx.exit(ngx.ERROR)
  else
    local ok, err = balancer.set_current_peer(table.unpack(upstream))
    if not ok then
      log_err('failed to set upstream: ', err)
      ngx.exit(ngx.ERROR)
    end
  end
end


return _M