Configure Resources

Resources may require provider-level data or remote system clients to operate correctly. The framework supports the ability to configure this data and/or clients once within the provider, then pass that information to resources by adding the Configure method.

Prepare Provider Configure Method

Implement the provider.ConfigureResponse.ResourceData field in the Provider interface Configure method. This value can be set to any type, whether an existing client or vendor SDK type, a provider-defined custom type, or the provider implementation itself. It is recommended to use pointer types so that resources can determine if this value was configured before attempting to use it.

During execution of the terraform plan and terraform apply commands, Terraform calls the provider ConfigureProvider RPC, in which the framework calls the provider.Provider interface Configure method.

In this example, the Go standard library net/http.Client is configured in the provider, and made available for resources:

// With the provider.Provider implementation
func (p *ExampleCloudProvider) Configure(ctx context.Context, req provider.ConfigureRequest, resp *provider.ConfigureResponse) {
  resp.ResourceData = &http.Client{/* ... */}
}

In this example, the code defines an ExampleClient type that is made available for resources:

type ExampleClient struct {
  /* ... */
}

// With the provider.Provider implementation
func (p *ExampleCloudProvider) Configure(ctx context.Context, req provider.ConfigureRequest, resp *provider.ConfigureResponse) {
  resp.ResourceData = &ExampleClient{/* ... */}
}

In this example, the ExampleCloudProvider type itself is made available for resources:

// With the provider.Provider implementation
type ExampleCloudProvider struct {
  /* ... */
}

func (p *ExampleCloudProvider) Configure(ctx context.Context, req provider.ConfigureRequest, resp *provider.ConfigureResponse) {
  resp.ResourceData = p
}

Define Resource Configure Method

Implement the resource.ResourceWithConfigure interface which receives the provider configured data from the Provider interface Configure method and saves it into the resource.Resource interface implementation.

The resource.ResourceWithConfigure interface Configure method is called during execution of the terraform validate, terraform plan and terraform apply commands when the ValidateResourceConfig RPC is sent. Additionally, the resource.ResourceWithConfigure interface Configure method is called during execution of the terraform plan and terraform apply commands when the ReadResource RPC is sent.

Note that Terraform calling the ValidateResourceConfig RPC would not call the ConfigureProvider RPC first, so implementations need to account for that situation. Configuration validation in Terraform occurs without provider configuration ("offline").

In this example, the provider configured the Go standard library net/http.Client which the resource uses during Read:

// With the resource.Resource implementation
type ThingResource struct {
  client *http.Client
}

func (r *ThingResource) Configure(ctx context.Context, req resource.ConfigureRequest, resp *resource.ConfigureResponse) {
  // Always perform a nil check when handling ProviderData because Terraform
  // sets that data after it calls the ConfigureProvider RPC.
  if req.ProviderData == nil {
    return
  }

  client, ok := req.ProviderData.(*http.Client)

  if !ok {
    resp.Diagnostics.AddError(
      "Unexpected Resource Configure Type",
      fmt.Sprintf("Expected *http.Client, got: %T. Please report this issue to the provider developers.", req.ProviderData),
    )

    return
  }

  r.client = client
}

func (r *ThingResource) Read(ctx context.Context, req resource.ReadRequest, resp *resource.ReadResponse) {
  // Prevent panic if the provider has not been configured.
  if r.client == nil {
    resp.Diagnostics.AddError(
      "Unconfigured HTTP Client",
      "Expected configured HTTP client. Please report this issue to the provider developers.",
    )

    return
  }

  httpResp, err := r.client.Get("https://example.com")
  /* ... */
}