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# Usage
The terraform configuration provides a simple way to start AWS EC2 instances
with the necessary software and configuration to run experiments.
As preparation please configure a proper ssh key in `rewan/module.tf` and
`rewan/server.user-data.yml`.
```
$ terraform init config-geo
$ terraform apply config-geo
$ ./extract_ips.py
... Use servers ...
$ terraform destroy config-geo
```
Warning: Seamless switching between configs is not always possible! Destroy the servers first if necessary.
# Setup Description
The `rewan` module contains the configuration for the VMs of a region whereas
`config-geo` contains the actual VM and regions setup in `config-geo`.
## VMs
The default instance type is configured in `rewan/variables.tf` and currently
defaults to a small t3 instance. The configuration uses spot instances with a
price limit of 0.02 dollars. In case a region has no spot capacity available
it is possible to use regular on-demand instances instead (on a per region basis).
The virtual machines run Ubuntu 18.04 and install Java 11, rsync/moreutils
(necessary for the experiment scripts), nethogs/iftop (network traffic
measurements) and chrony (NTP time synchronization). The software installation
can run for a few minutes after VM startup.
The firewall of each VM allows access via SSH, permits pinging the VMs and opens
TCP ports 8170-8199 for connections between the replicas.
## Region Setup
The region setup for starting VMs in `config-geo` consists of three setup steps:
1. Configure a `provider` for each region.
2. Include the `rewan` module for each region and configure it to use the matching
provider. The subnet specification configures the VPC subnets which also specify
a VMs region. The module creates `counts` VMs, which are assigned to VPC subnets
from first to last. If there are more VMs than subnets, then these VMs are added
to the last subnet.
3. Finally, add the rewan module to the `outregs` variable. This allows the
`extract_ips.py` to retrieve the VMs internal and external IPs.