Terraform Core And Plugins
Terraform is logically split into two main parts: Terraform Core and Terraform Plugins. Terraform Core uses remote procedure calls (RPC) to communicate with Terraform Plugins, and offers multiple ways to discover and load plugins to use. Terraform Plugins expose an implementation for a specific service, such as AWS, or provisioner, such as bash.
Terraform Core
Terraform Core is a statically-compiled binary written in the Go programming language. The compiled binary is the command line tool (CLI) terraform, the entrypoint for anyone using Terraform.
Responsibilities of terraform Core
- Infrastructure as code: reading and interpolating configuration files and modules
- Resource state management
- Plan execution
- Construction of the Resource Graph
- Communication with plugins over RPC
Terraform Plugins
Terraform Plugins are written in Go and are executable binaries invoked by Terraform Core over RPC. Each plugin exposes an implementation for a specific service, such as AWS, or provisioner, such as bash.
All Providers and Provisioners used in Terraform configurations are plugins.
They are executed as a separate process and communicate with the main Terraform binary over an RPC interface.
Terraform has several Provisioners built-in, while Providers are discovered dynamically as needed.
Terraform Core provides a high-level framework that abstracts away the details of plugin discovery and RPC communication so developers do not need to manage either.
Terraform Plugins are responsible for the domain-specific implementation of their type.
Responsibilities of Provider Plugins are
- Initialization of any included libraries used to make API calls
- Authentication with the Infrastructure Provider
- Define Resources that map to specific Services
Responsibilities of Provisioner Plugins are
- Executing commands or scripts on the designated Resource after creation, or on destruction.