Erlang load balancer

Use cases

In case you have tasks of different heaviness, do not know your load limits and spawn as many threads, as possible - use it. In any other situations - use poolboy, jobs, rabbitmq, pool or others.

Worker Configuration

There is no need to configure worker for getting statistics. Just sure, that os_mon application is started and eloadbalc is added as a rebar dep.

Balancer Configuration

Add eloadbalc as a rebar dep. Balancer system will use logic selection code and storing system metrics, while worker server will just execute code for getting metrics.
Sample configuration:

{
    Metric,
    [{Node, ConnectTime, UpdateTime, MaxValue}]
}

Where Metric is atom cpu, ram or counter.
cpu means that logic will collect cpu load percentage from all of your worker nodes.
ram will collect free memory percentage.
counter will collect statistics of run queue.
Node is your node name with address, as an atom, f.e. eloadbalc@127.0.0.1.
ConnectTime is a time for your balancer node to connect to worker. When node is down and error {badrpc, nodedown} is got

• this time is used against UpdateTime. Important! Do not set this time too little, as often rpc calls can prevent your worker node from starting.
  UpdateTime is an atom realtime or integer value in milliseconds, means update frequency of statistics. Realtime requests will ask node on every get_less_loaded node request. They are more direct, but can produce load themselves.
  MaxValue is an integer value of maximum load. If current load exceeds this value - node will be turned off - and won't act in get_less_loaded calls.
  If you want to add your nodes after configuring balancer - use eloadbalc:add_node/3. It takes these parameters: Node, MaxValue, UpdateTime.

Usage

To connect eloadbalc to your app - add eloadbalc_sup to your supervision tree, and pass the configuration to it. It will start one server per your balancer system node. Than you can use eloadbalc:get_less_loaded/0 to obtain less loaded node, or eloadbalc:get_less_loaded_random/0 to get random from less loaded nodes with 5% delta.

Troubleshooting

If eb_logic_worker can't connect to remote node for statistics collection and you get badrpc error - first chech if rpc protocol is allowed in your network firewall rules and two nodes have the same secret.
If nodes can connect to each other, but you can't call eb_collector - check if it's code is loaded in the system. Simply call eb_collector:collect... when your application start for loading the code.