---
title: "Network Load balancer"
weight: 1
---

## Introduction
Load balancer is a key component of the network. It distributes all the incoming traffic across any set of components like EC2 instances, DB, etc. 

In this workshop we will create.  

* External Load balancer     - **```1```** 
* Internal Load balancer     - **```1```** 

***aws_lb*** terraform resource will be used to create the load balancer.  

```console
resource "aws_lb" "external-lb" {
  name                             = "External-LB"
  load_balancer_type               = "network"
  internal                         = false
  enable_cross_zone_load_balancing = "true"
  subnets                          = var.outside_subnet_id
}
```

1. Notice that the external load balancer points towards the outside subnet.
2. Enabling cross zone load balancing is crucial to make sure that requests are evenly split between all the availability zones used. 
3. Set the internal attribute to false for the internet facing load balancer. 
   
  ![load_balancers](/static/images/deploy_loadbalancers/lb.jpeg) 

Following are the variables created to set port and protocol on which the load balancer will listen to and use for checking health status of tartget instances

```console
variable "external_listener_ports" {
  default = [{
    protocol = "TCP"
    port = 22
    target_type = "ip"
  }]
}
variable "external_health_check" {
  default = {
    protocol = "TCP"
    port     = 80
  }
}
```

The load balancer will require some targets to route requests to, to create a target group we use the ***aws_lb_target_group*** terraform resource.

```console
resource "aws_lb_target_group" "external_front_end" {
  for_each    = {for k, v in var.external_listener_ports : k => v}
  name        = tostring("external-${each.key}")
  port        = each.value.port
  protocol    = each.value.protocol
  target_type = each.value.target_type
  vpc_id      = var.vpc_id

  health_check {
    interval = 30
    protocol = var.external_health_check.protocol
    port     = var.external_health_check.port
  }
}
```    
  ![target_groups](/static/images/deploy_loadbalancers/target_groups.jpeg) 
  
--> We can change the attributes of ```heath_check ```attachment as per specific needs.



Attaching targets to the target group:

```console
resource "aws_lb_target_group_attachment" "target1" {
  count            = length(var.ftd_outside_ip)
  depends_on       = [aws_lb_target_group.external_front_end]
  target_group_arn = aws_lb_target_group.external_front_end[0].arn
  target_id        = var.ftd_outside_ip[count.index]
}
```

To configure the port and protocol the load balancer should listen on, we use ***aws_lb_listener*** (exists for App-lb as well)terraform resource.  
It will allow the loadbalancer to listen to certain ports and protocols

```console
resource "aws_lb_listener" "external_listener" {
  for_each  = { for k, v in var.external_listener_ports : k => v }
  load_balancer_arn = aws_lb.external-lb[0].arn
  port              = each.value.port
  protocol          = each.value.protocol
  default_action {
    type             = "forward"
    target_group_arn = aws_lb_target_group.external_front_end[each.key].arn
  }
}
```

1. We add the ARN of load balancer and the ports and protocols desired. 
2. Target group is also attached as the part of ***default_action***.