> ## Documentation Index
> Fetch the complete documentation index at: https://www.ravion.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.
# Modules
> Modules are the core Ravion primitive that defines, tracks, and manages a piece of infrastructure, from a database to a full application.
A module is the core primitive in Ravion for both tracking and managing your services and supporting infrastructure.
A module's definition determines which **capabilities** its instances have — a Terraform stack, build config, deploy manager, and so on:
```mermaid theme={null}
%%{init: {'flowchart': {'defaultRenderer': 'elk'}}}%%
flowchart LR
Module[Module] -. optional .-> IaCState["Stack (Terraform state)
"]
Module -. optional .-> BuildConfig["Build config
"]
Module -. optional .-> DeployManager["Deploy manager
"]
Module -. optional .-> CertificateDomain["Certificate & domain manager
"]
Module -. optional .-> MetricCharts["Metric charts
"]
Module -. optional .-> Logs["Logs
"]
Module -. optional .-> Links["Links
"]
class Module container
class IaCState,BuildConfig,DeployManager,CertificateDomain,MetricCharts,Logs,Links module
classDef container fill:#FE6104,stroke:#BD4406,color:#fff
classDef module fill:#F6DDCE,stroke:#FE6104,color:#2a1208
click IaCState "/modules/stack" "Open stack docs"
click BuildConfig "/modules/build" "Open build docs"
click DeployManager "/modules/deploy" "Open deploy docs"
click CertificateDomain "/modules/deploy" "Open deploy docs"
click MetricCharts "/modules/metrics" "Open metrics docs"
click Logs "/modules/logs" "Open logs docs"
```
For example, our **VPC Network** module has only a stack. But the **ECS Web Server** module has *all* of the above capabilities.
For how modules relate to stacks, deploys, and pipelines, see [Core concepts](/concepts/core-concepts).
By default, you have access to the Ravion [standard library](/module-definitions/standard-library) of module definitions. You can see the available module definitions via the *Catalog* page in the dashboard or via the `/module-definitions` endpoint.
You can also create your own module definitions.
## Module hierarchy
*Catalog* is used to refer to the module definitions available to your organization. These include the Ravion [standard library](/module-definitions/standard-library) of modules with type `rvn-*` and any custom modules you've added.
Module definitions are versioned with semver, and each module instance is an instance of a specific version.
```mermaid theme={null}
flowchart
OrgCatalog[Organization catalog] -- contains --> StandardModules[Standard modules of type rvn-*]
OrgCatalog -- contains --> CustomModules[Custom modules]
StandardModules --> ModuleDefinition[Module definition]
CustomModules --> ModuleDefinition
ModuleDefinition -- has many --> ModuleVersion[Module version]
ModuleInstance[Module instance] -- of --> ModuleVersion
class OrgCatalog catalog
class StandardModules,CustomModules source
class ModuleDefinition,ModuleVersion,ModuleInstance module
classDef catalog fill:#FE6104,stroke:#BD4406,color:#fff
classDef source fill:#1f2937,stroke:#111827,color:#fff
classDef module fill:#F6DDCE,stroke:#FE6104,color:#2a1208
```