# Load Balancers
  
  A **load balancer** is a device that distributes incoming network traffic amongst
  multiple back-end systems. These back-end systems are called the **nodes** of
  the load balancer.
  
  ## Getting started
  
  ### 1. Instantiate a Rackspace client.
  
  ```php
  
  use OpenCloud\Rackspace;
  
  $client = new Rackspace(Rackspace::US_IDENTITY_ENDPOINT, array(
      'username' => '<YOUR RACKSPACE CLOUD ACCOUNT USERNAME'>,
      'apiKey'   => '<YOUR RACKSPACE CLOUD ACCOUNT API KEY>'
  ));
  ```
  
  ### 2. Retrieve the server instances you want to add as nodes of the load balancer.
  
  ```php
  $computeService = $client->computeService('cloudServersOpenStack', 'DFW');
  
  $serverOne = $computeService->server('e836fc4e-056d-4447-a80e-fefcaa640216');
  $serverTwo = $computeService->server('5399cd36-a23f-41a6-bdf7-20902aec0e74');
  ```
  
  The example above uses two server instances that have already been created. It
  retrieves the server instances using their IDs. See also: [creating server instances]().
  
  ### 3. Obtain a Load Balancer service object from the client.
  
  This object will be used to first define the load balancer nodes and later create the load balancer itself.
  
  ```php
  $loadBalancerService = $client->loadBalancerService('cloudLoadBalancers', 'DFW');
  ```
  
  ### 4. Define a load balancer node for each server.
  
  ```php
  $loadBalancer = $loadBalancerService->loadBalancer();
  
  $serverOneNode = $loadBalancer->node();
  $serverOneNode->address = $serverOne->addresses->private[0]->addr;
  $serverOneNode->port = 8080;
  $serverOneNode->condition = 'ENABLED';
  
  $serverTwoNode = $loadBalancer->node();
  $serverTwoNode->address = $serverTwo->addresses->private[0]->addr;
  $serverTwoNode->port = 8080;
  $serverTwoNode->condition = 'ENABLED';
  ```
  
  In the example above, each node runs a service that listens on port 8080. Further, 
  each node will start out as `ENABLED`, which means it will be ready to receive
  network traffic from the load balancer as soon as it is created.
  
  ### 5. Create the load balancer with the two nodes.
  
  ```php
  $loadBalancer->addVirtualIp('PUBLIC');
  $loadBalancer->create(array(
      'name' => 'My smart load balancer',
      'port' => 80,
      'protocol' => 'HTTP',
      'nodes' => array($serverOneNode, $serverTwoNode)
  ));
  ```
  
  In the example above, the load balancer will have a virtual IP address accessible 
  from the public Internet. Also notice that the port the load balancer listens
  on (80) does not need to match the ports of its nodes (8080).
  
  ## Next steps
  
  Once you have created a load balancer, there is a lot you can do with it. See 
  the [complete user guide for load balancers](USERGUIDE.md).