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Part 3 - Demos, Testing and Healthchecks.

In Part II we continued from single web EC2 instance, to an Auto-Scaling Load Balanced cluster of EC2 instances.

note

You need the pre-requisites and setup from Part I before you can follow along.

Terraform files​

The terraform files you should have to work with are as follows

  • auto.scaling.group.tf
  • elastic.load.balancer.tf
  • launch.configuration.tf
  • output.tf
  • provider.tf
  • security.groups.tf
  • variables.tf

Video Example of Launch​

The Plan is good, it's time to launch our plan into the Cloud/AWS.

The bottom screen shows a watch aws ec2 describe-instance-status command which shows the moment an EC2 instance is born:

The output.tf config had the ELB's public DNS outputted so we can go and connect to it.

EC2 Cluster of Web Servers​

Check everything's launched as we needed and the web servers are serving our web page:

Test Auto Scaling Setting​

Let's test the Autoscaling Group by killing one instance, and watch ASG launch another instance (remember the minimum acceptable instances is 2):

What was new/different from the previous configs? I've noted some of the changes below.

Added healthchecks​

These are cool. It tells the Load Balancer what's a "healthy" number of EC2 instances we want running(2 is the magic number here), sets timeout values and intervals.

# elastic.load.balancer.tf
resource "aws_elb" "ElasticLoadBalancer" {
  name = "ELBAutoScalingGroup"
  security_groups = ["${aws_security_group.ELBSecurityGroup.id}"]
  availability_zones = ["${data.aws_availability_zones.available.names}"]

  health_check {
    healthy_threshold = 2
    unhealthy_threshold = 2
    timeout = 3
    interval = 30
    target = "HTTP:${var.inbound_port}/"
  }

  listener {
    lb_port = 80
    lb_protocol = "http"
    instance_port = "${var.inbound_port}"
    instance_protocol = "http"
  }
}

ELB: Healthchecks Targeting EC2's​

AWS healthchecks are essentially "pings" to the EC2 endpoints defined by the 'target' parameter.

  • 'HTTP' is the ping protocol
  • 'var.inbound_port' is the ping port
  • the ping PATH the '/' on the end.

Interpolating count for EC2 instance names (failed)​

Well this failed miserably. I wanted to have each EC2 fire up with a unique name. Need to look into this more, but from the little I've read up on this approach it might not be the way to go.

Anyway, the new changes:

variables.tf

variable "count" {
  default = 1
}

auto.scaling.group.tf (note 'tags' not 'tag')

tags {
    Name = "${format("ASG-%03d", count.index + 1)}"
    propagate_at_launch = true
}

Conclusion​

Overall this was a really good basic steps exercise in getting familiar with the building blocks of Terraform. It's a really great infrastructure management platform and I think one that I'm going to get properly familiar with and I definitely recommend it as part of your DevOps toolchain.

References​

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