Production-Grade (ish) server orchestration with Kamal

This is the architecture of our small cluster:

Architecture

It creates two servers: web where our application lives and accessories where our dependencies like databases and caches live. web exposes ports 80, 22 and 443, while accessories is not accessible from the outside. Root access is disabled on both machines and only the kamal user can SSH into them.

You can create more servers by updating web_servers_count or accessories_count in variables.tf. If there is more than one web server, a load balancer will be created and all the web servers will be added to it.

In case multiple servers of different types are created, the naming will be web-1, web-2, accessories-1, and accessories-2, as opposed to web, accessories, the default naming convention.

Important

If you are copying this workflow, you should change the SSH keys in cloudinit/base.yml to your own. It is defined on ssh_import_id and imports the SSH keys from your GitHub account.

Connecting to the servers

After running terraform apply, the script will output an SSH configuration that can be copied to your ~/.ssh/config file. This is to help you connect to servers since accessory servers are not accessible from the outside, you need to use the web server as a jump host. It looks like this:

ssh_01_web_config = <<EOT
Host web-1
  HostName 167.235.61.121
  User kamal
Host web-2
  HostName 5.75.160.210
  User kamal
EOT
ssh_02_accessories_config = <<EOT
Host accessories-1
  HostName 78.46.225.17
  User kamal
  ProxyJump web-1
Host accessories-2
  HostName 167.235.156.173
  User kamal
  ProxyJump web-1
Host accessories-3
  HostName 128.140.70.80
  User kamal
  ProxyJump web-1
EOT

The machines

All machines are CPX11: 2 AMD vCPUs, 2 GB of RAM and 40 GB of SSD storage, running Ubuntu 24.04. See variables.tf for more details and how to change them.

Price

The default setup of 1 web server and 1 accessory server will cost you around 10 EUR/month.

How to use it

1. Clone
2. Create a file terraform.tfvars with your credentials, it will look like this:

hetzner_api_key = "your-api-key"

3. Update the cloudinit/base.yml file with your SSH keys (line #23)
4. Run terraform init
5. Run terraform plan (optional)
6. Run terraform apply