How can I automatically scale my Droplets based on CPU usage using Terraform and DigitalOcean?

Hey!

Great question! Indeed, as you mentioned, while DigitalOcean doesn’t have native auto-scaling for Droplets, you can still achieve something similar by combining Terraform with monitoring tools like DigitalOcean’s Monitoring and external automation for scaling.

1. First, set up DigitalOcean Monitoring or an external monitoring tool like Prometheus to keep track of CPU usage on your Droplets. DigitalOcean Monitoring can trigger alerts when CPU thresholds are exceeded, which is key for deciding when to scale up or down:

https://docs.digitalocean.com/products/monitoring/

2. Once you have the monitoring in place, since Terraform isn’t event-driven, you’ll need to use a cron job, CI/CD pipeline (like GitHub Actions or Jenkins), or another automation tool to trigger Terraform runs. The idea is to monitor the CPU usage and, when the usage crosses a defined threshold, trigger Terraform to either scale up by creating more Droplets or scale down by destroying unnecessary ones.

Here’s an example of how you can use a variable in Terraform to control the number of Droplets:

variable "droplet_count" {
  default = 1
}

resource "digitalocean_droplet" "web" {
  count  = var.droplet_count
  name   = "web-${count.index + 1}"
  image  = "ubuntu-20-04-x64"
  region = "nyc3"
  size   = "s-1vcpu-1gb"
}

In this case, the droplet_count variable will control how many Droplets are created. You can modify this value dynamically based on the CPU usage and then trigger a Terraform apply.

3. To distribute traffic across the Droplets, use DigitalOcean’s Load Balancers. Here’s how you can set up a load balancer using Terraform:

resource "digitalocean_loadbalancer" "lb" {
  name   = "web-lb"
  region = "nyc3"

  forwarding_rule {
    entry_port      = 80
    entry_protocol  = "http"
    target_port     = 80
    target_protocol = "http"
  }

  droplet_ids = digitalocean_droplet.web[*].id
}

This will provide a way to “auto-scale” your Droplets based on demand, even though it’s not built into DigitalOcean’s platform natively.

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On another note, if you’re just getting started with Terraform and DigitalOcean, this ebook might be helpful: Introduction to Terraform ebook.

Let me know if you have any other questions, and good luck with your project!

- Bobby