Consul-Terraform-Sync is a service-oriented tool for managing network infrastructure near real-time. Consul-Terraform-Sync runs as a daemon and integrates the network topology maintained by your Consul cluster with your network infrastructure to dynamically secure and connect services.
»10,000 Foot View
The diagram shows Consul-Terraform-Sync monitoring the Consul service catalog for updates and utilizing Terraform to update the state of the infrastructure.
There are two principal aspects of Sync to know about corresponding to the lines to Consul and Terraform in the diagram above. The line to Consul represents the Watchers monitoring the state of Consul's service catalog (and possibly KV store) while the line to Terraform represents tasks being run to update the infrastructure.
»Watcher and Views
Consul-Terraform-Sync monitors Consul for updates utilizing Consul's Blocking Queries whenever supported, falling back on polling when not. The watcher maintains a separate thread (known internally as a view) for each value monitored, running any tasks that depend on that watched value whenever it's updated. Say, for example, running a task to update a proxy when an instance goes unhealthy.
A task is the action triggered by the updated data monitored in Consul. It takes the that dynamic service data and translates it into a call to the infrastructure application to configure it with the updates. It uses a driver to push out these updates, the initial driver being a local Terraform run. An example of a task is to automate a firewall security policy rule with discovered IP addresses for a set of Consul services.
A driver encapsulates the resources required to communicate the updates to the network infrastructure. Terraform is the initial supported driver. It comes with a set of providers that enables supporting a wide variety of infrastructure applications.
The Secure Consul-Terraform-Sync for Production tutorial contains a checklist of best practices to secure your Consul-Terraform-Sync installation for a production environment.