doc: Adds documentation and example for mongodbatlas_flex_cluster resource and data source

docs/data-sources/flex_cluster.md

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+# Data Source: mongodbatlas_flex_cluster
+
+`mongodbatlas_flex_cluster` describes a flex cluster.
+
+## Example Usages
+```terraform
+resource "mongodbatlas_flex_cluster" "example-cluster" {
+  project_id = var.project_id
+  name       = var.cluster_name
+  provider_settings = {
+    backing_provider_name = "AWS"
+    region_name           = "US_EAST_1"
+  }
+  termination_protection_enabled = true
+}
+
+data "mongodbatlas_flex_cluster" "example-cluster" {
+  project_id = var.project_id
+  name       = mongodbatlas_flex_cluster.example-cluster.name
+}
+
+data "mongodbatlas_flex_clusters" "example-clusters" {
+  project_id = var.project_id
+}
+
+output "mongodbatlas_flex_cluster" {
+  value = data.mongodbatlas_flex_cluster.example-cluster.name
+}
+
+output "mongodbatlas_flex_clusters_names" {
+  value = [for cluster in data.mongodbatlas_flex_clusters.example-clusters.results : cluster.name]
+}
+```
+
+<!-- schema generated by tfplugindocs -->
+## Schema
+
+### Required
+
+- `name` (String) Human-readable label that identifies the flex cluster.
+- `project_id` (String) Unique 24-hexadecimal digit string that identifies your project. Use the [/groups](#tag/Projects/operation/listProjects) endpoint to retrieve all projects to which the authenticated user has access.
+
+**NOTE**: Groups and projects are synonymous terms. Your group id is the same as your project id. For existing groups, your group/project id remains the same. The resource and corresponding endpoints use the term groups.
+
+### Read-Only
+
+- `backup_settings` (Attributes) Flex backup configuration (see [below for nested schema](#nestedatt--backup_settings))
+- `cluster_type` (String) Flex cluster topology.
+- `connection_strings` (Attributes) Collection of Uniform Resource Locators that point to the MongoDB database. (see [below for nested schema](#nestedatt--connection_strings))
+- `create_date` (String) Date and time when MongoDB Cloud created this instance. This parameter expresses its value in ISO 8601 format in UTC.
+- `id` (String) Unique 24-hexadecimal digit string that identifies the instance.
+- `mongo_db_version` (String) Version of MongoDB that the instance runs.
+- `provider_settings` (Attributes) Group of cloud provider settings that configure the provisioned MongoDB flex cluster. (see [below for nested schema](#nestedatt--provider_settings))
+- `state_name` (String) Human-readable label that indicates the current operating condition of this instance.
+- `tags` (Map of String) Map that contains key-value pairs between 1 to 255 characters in length for tagging and categorizing the instance.
+- `termination_protection_enabled` (Boolean) Flag that indicates whether termination protection is enabled on the cluster. If set to `true`, MongoDB Cloud won't delete the cluster. If set to `false`, MongoDB Cloud will delete the cluster.
+- `version_release_system` (String) Method by which the cluster maintains the MongoDB versions.
+
+<a id="nestedatt--backup_settings"></a>
+### Nested Schema for `backup_settings`
+
+Read-Only:
+
+- `enabled` (Boolean) Flag that indicates whether backups are performed for this flex cluster. Backup uses [TODO](TODO) for flex clusters.
+
+
+<a id="nestedatt--connection_strings"></a>
+### Nested Schema for `connection_strings`
+
+Read-Only:
+
+- `standard` (String) Public connection string that you can use to connect to this cluster. This connection string uses the mongodb:// protocol.
+- `standard_srv` (String) Public connection string that you can use to connect to this flex cluster. This connection string uses the `mongodb+srv://` protocol.
+
+
+<a id="nestedatt--provider_settings"></a>
+### Nested Schema for `provider_settings`
+
+Read-Only:
+
+- `backing_provider_name` (String) Cloud service provider on which MongoDB Cloud provisioned the flex cluster.
+- `disk_size_gb` (Number) Storage capacity available to the flex cluster expressed in gigabytes.
+- `provider_name` (String) Human-readable label that identifies the cloud service provider.
+- `region_name` (String) Human-readable label that identifies the geographic location of your MongoDB flex cluster. The region you choose can affect network latency for clients accessing your databases. For a complete list of region names, see [AWS](https://docs.atlas.mongodb.com/reference/amazon-aws/#std-label-amazon-aws), [GCP](https://docs.atlas.mongodb.com/reference/google-gcp/), and [Azure](https://docs.atlas.mongodb.com/reference/microsoft-azure/).
+
+For more information see: [MongoDB Atlas API - Flex Cluster](https://www.mongodb.com/docs/atlas/reference/api-resources-spec/#tag/Flex-Clusters/operation/getFlexCluster) Documentation.

docs/data-sources/flex_clusters.md

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+# Data Source: mongodbatlas_flex_clusters
+
+`mongodbatlas_flex_clusters` returns all flex clusters in a project.
+
+## Example Usages
+```terraform
+resource "mongodbatlas_flex_cluster" "example-cluster" {
+  project_id = var.project_id
+  name       = var.cluster_name
+  provider_settings = {
+    backing_provider_name = "AWS"
+    region_name           = "US_EAST_1"
+  }
+  termination_protection_enabled = true
+}
+
+data "mongodbatlas_flex_cluster" "example-cluster" {
+  project_id = var.project_id
+  name       = mongodbatlas_flex_cluster.example-cluster.name
+}
+
+data "mongodbatlas_flex_clusters" "example-clusters" {
+  project_id = var.project_id
+}
+
+output "mongodbatlas_flex_cluster" {
+  value = data.mongodbatlas_flex_cluster.example-cluster.name
+}
+
+output "mongodbatlas_flex_clusters_names" {
+  value = [for cluster in data.mongodbatlas_flex_clusters.example-clusters.results : cluster.name]
+}
+```
+
+<!-- schema generated by tfplugindocs -->
+## Schema
+
+### Required
+
+- `project_id` (String) Unique 24-hexadecimal digit string that identifies your project. Use the [/groups](#tag/Projects/operation/listProjects) endpoint to retrieve all projects to which the authenticated user has access.
+
+**NOTE**: Groups and projects are synonymous terms. Your group id is the same as your project id. For existing groups, your group/project id remains the same. The resource and corresponding endpoints use the term groups.
+
+### Read-Only
+
+- `results` (Attributes List) List of returned documents that MongoDB Cloud provides when completing this request. (see [below for nested schema](#nestedatt--results))
+
+<a id="nestedatt--results"></a>
+### Nested Schema for `results`
+
+Read-Only:
+
+- `backup_settings` (Attributes) Flex backup configuration (see [below for nested schema](#nestedatt--results--backup_settings))
+- `cluster_type` (String) Flex cluster topology.
+- `connection_strings` (Attributes) Collection of Uniform Resource Locators that point to the MongoDB database. (see [below for nested schema](#nestedatt--results--connection_strings))
+- `create_date` (String) Date and time when MongoDB Cloud created this instance. This parameter expresses its value in ISO 8601 format in UTC.
+- `id` (String) Unique 24-hexadecimal digit string that identifies the instance.
+- `mongo_db_version` (String) Version of MongoDB that the instance runs.
+- `name` (String) Human-readable label that identifies the flex cluster.
+- `project_id` (String) Unique 24-hexadecimal digit string that identifies your project. Use the [/groups](#tag/Projects/operation/listProjects) endpoint to retrieve all projects to which the authenticated user has access.
+
+**NOTE**: Groups and projects are synonymous terms. Your group id is the same as your project id. For existing groups, your group/project id remains the same. The resource and corresponding endpoints use the term groups.
+- `provider_settings` (Attributes) Group of cloud provider settings that configure the provisioned MongoDB flex cluster. (see [below for nested schema](#nestedatt--results--provider_settings))
+- `state_name` (String) Human-readable label that indicates the current operating condition of this instance.
+- `tags` (Map of String) Map that contains key-value pairs between 1 to 255 characters in length for tagging and categorizing the instance.
+- `termination_protection_enabled` (Boolean) Flag that indicates whether termination protection is enabled on the cluster. If set to `true`, MongoDB Cloud won't delete the cluster. If set to `false`, MongoDB Cloud will delete the cluster.
+- `version_release_system` (String) Method by which the cluster maintains the MongoDB versions.
+
+<a id="nestedatt--results--backup_settings"></a>
+### Nested Schema for `results.backup_settings`
+
+Read-Only:
+
+- `enabled` (Boolean) Flag that indicates whether backups are performed for this flex cluster. Backup uses [TODO](TODO) for flex clusters.
+
+
+<a id="nestedatt--results--connection_strings"></a>
+### Nested Schema for `results.connection_strings`
+
+Read-Only:
+
+- `standard` (String) Public connection string that you can use to connect to this cluster. This connection string uses the mongodb:// protocol.
+- `standard_srv` (String) Public connection string that you can use to connect to this flex cluster. This connection string uses the `mongodb+srv://` protocol.
+
+
+<a id="nestedatt--results--provider_settings"></a>
+### Nested Schema for `results.provider_settings`
+
+Read-Only:
+
+- `backing_provider_name` (String) Cloud service provider on which MongoDB Cloud provisioned the flex cluster.
+- `disk_size_gb` (Number) Storage capacity available to the flex cluster expressed in gigabytes.
+- `provider_name` (String) Human-readable label that identifies the cloud service provider.
+- `region_name` (String) Human-readable label that identifies the geographic location of your MongoDB flex cluster. The region you choose can affect network latency for clients accessing your databases. For a complete list of region names, see [AWS](https://docs.atlas.mongodb.com/reference/amazon-aws/#std-label-amazon-aws), [GCP](https://docs.atlas.mongodb.com/reference/google-gcp/), and [Azure](https://docs.atlas.mongodb.com/reference/microsoft-azure/).
+
+For more information see: [MongoDB Atlas API - Flex Clusters](https://www.mongodb.com/docs/atlas/reference/api-resources-spec/v2/#tag/Streams/operation/listFlexClusters) Documentation.

docs/guides/flex-cluster-to-dedicated-cluster-migraton-guide.md

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+---
+page_title: "Migration Guide: Flex Cluster to Dedicated Cluster"
+---
+
+# Migration Guide: Flex Cluster to Dedicated Cluster
+
+**Objective**: This guide explains how to replace the `mongodbatlas_flex_cluster` resource with the `mongodbatlas_advanced_cluster` resource.
+
+Currently, the only method to migrate your Flex cluster to a Dedicated cluster is via the Atlas UI.
+
+<!-- Noting that implementation of flex_cluster as a part of mongodb_advanced_cluster in January 2025 will create new migration journey -->
+
+## Best Practices Before Migrating
+Before doing any migration, create a backup of your [Terraform state file](https://developer.hashicorp.com/terraform/cli/commands/state).
+
+### Procedure
+
+
+See [Modify a Cluster](https://www.mongodb.com/docs/atlas/scale-cluster/) for how to migrate via the Atlas UI.
+
+Complete the following procedure to resolves the configuration drift in Terraform. This does not affect the underlying cluster infrastructure.
+
+1. Find the import IDs of the new Dedicated cluster your Flex cluster has migrated to: `{PROJECT_ID}-{CLUSTER_NAME}`, such as `664619d870c247237f4b86a6-clusterName`
+2. Add an import block to one of your `.tf` files:
+  ```terraform
+  import {
+    to = mongodbatlas_advanced_cluster.this
+    id = "664619d870c247237f4b86a6-clusterName" # from step 1
+  }
+  ```
+  3. Run `terraform plan -generate-config-out=adv_cluster.tf`. This should generate a `adv_cluster.tf` file.
+  4. Run `terraform apply`. You should see the resource imported: `Apply complete! Resources: 1 imported, 0 added, 0 changed, 0 destroyed.`
+  5. Remove the "default" fields. Many fields of this resource are optional. Look for fields with a `null` or `0` value or blocks you didn't specify before. Required fields have been outlined in the below example resource block:
+      ``` terraform
+      resource "mongodbatlas_advanced_cluster" "this" {
+         cluster_type = "REPLICASET"
+         name         = "clusterName"
+         project_id   = "664619d870c247237f4b86a6"
+         replication_specs {
+            zone_name = "Zone 1"
+            region_configs {
+               priority      = 7
+               provider_name = "AWS"
+               region_name   = "EU_WEST_1"
+               analytics_specs {
+                  instance_size = "M10"
+                  node_count    = 0
+               }
+               electable_specs {
+                  instance_size = "M10"
+                  node_count    = 3
+               }
+            }
+         }
+      }
+      ```
+   6. Re-use existing [Terraform expressions](https://developer.hashicorp.com/terraform/language/expressions). All fields in the generated configuration have static values. Look in your previous configuration for:
+      - variables, for example: `var.project_id`
+      - Terraform keywords, for example: `for_each`, `count`, and `depends_on`
+  7. Re-run `terraform apply` to ensure you have no planned changes: `No changes. Your infrastructure matches the configuration.`
+  8. Update the references from your previous cluster resource: `mongodbatlas_flex_cluster.this.X` to the new `mongodbatlas_advanced_cluster.this.X`.
+  9. Update any data source blocks to refer to `mongodbatlas_advanced_cluster`.
+  10. Replace your existing clusters with the ones from `adv_cluster.tf` and run `terraform state rm mongodbatlas_flex_cluster.this`. Without this step, Terraform creates a plan to delete your existing cluster.
+  11.  Remove the import block created in step 2.
+  12.  Re-run `terraform apply` to ensure you have no planned changes: `No changes. Your infrastructure matches the configuration.`

docs/resources/flex_cluster.md

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+# Resource: mongodbatlas_flex_cluster
+
+`mongodbatlas_flex_cluster` provides a Flex Cluster resource. The resource lets you create, update, delete and import a flex cluster.
+
+## Example Usages
+
+```terraform
+resource "mongodbatlas_flex_cluster" "example-cluster" {
+  project_id = var.project_id
+  name       = var.cluster_name
+  provider_settings = {
+    backing_provider_name = "AWS"
+    region_name           = "US_EAST_1"
+  }
+  termination_protection_enabled = true
+}
+
+data "mongodbatlas_flex_cluster" "example-cluster" {
+  project_id = var.project_id
+  name       = mongodbatlas_flex_cluster.example-cluster.name
+}
+
+data "mongodbatlas_flex_clusters" "example-clusters" {
+  project_id = var.project_id
+}
+
+output "mongodbatlas_flex_cluster" {
+  value = data.mongodbatlas_flex_cluster.example-cluster.name
+}
+
+output "mongodbatlas_flex_clusters_names" {
+  value = [for cluster in data.mongodbatlas_flex_clusters.example-clusters.results : cluster.name]
+}
+```
+
+<!-- schema generated by tfplugindocs -->
+## Schema
+
+### Required
+
+- `name` (String) Human-readable label that identifies the instance.
+- `project_id` (String) Unique 24-hexadecimal character string that identifies the project.
+- `provider_settings` (Attributes) Group of cloud provider settings that configure the provisioned MongoDB flex cluster. (see [below for nested schema](#nestedatt--provider_settings))
+
+### Optional
+
+- `tags` (Map of String) Map that contains key-value pairs between 1 to 255 characters in length for tagging and categorizing the instance.
+- `termination_protection_enabled` (Boolean) Flag that indicates whether termination protection is enabled on the cluster. If set to `true`, MongoDB Cloud won't delete the cluster. If set to `false`, MongoDB Cloud will delete the cluster.
+
+### Read-Only
+
+- `backup_settings` (Attributes) Flex backup configuration (see [below for nested schema](#nestedatt--backup_settings))
+- `cluster_type` (String) Flex cluster topology.
+- `connection_strings` (Attributes) Collection of Uniform Resource Locators that point to the MongoDB database. (see [below for nested schema](#nestedatt--connection_strings))
+- `create_date` (String) Date and time when MongoDB Cloud created this instance. This parameter expresses its value in ISO 8601 format in UTC.
+- `id` (String) Unique 24-hexadecimal digit string that identifies the instance.
+- `mongo_db_version` (String) Version of MongoDB that the instance runs.
+- `state_name` (String) Human-readable label that indicates the current operating condition of this instance.
+- `version_release_system` (String) Method by which the cluster maintains the MongoDB versions.
+
+<a id="nestedatt--provider_settings"></a>
+### Nested Schema for `provider_settings`
+
+Required:
+
+- `backing_provider_name` (String) Cloud service provider on which MongoDB Cloud provisioned the flex cluster.
+- `region_name` (String) Human-readable label that identifies the geographic location of your MongoDB flex cluster. The region you choose can affect network latency for clients accessing your databases. For a complete list of region names, see [AWS](https://docs.atlas.mongodb.com/reference/amazon-aws/#std-label-amazon-aws), [GCP](https://docs.atlas.mongodb.com/reference/google-gcp/), and [Azure](https://docs.atlas.mongodb.com/reference/microsoft-azure/).
+
+Read-Only:
+
+- `disk_size_gb` (Number) Storage capacity available to the flex cluster expressed in gigabytes.
+- `provider_name` (String) Human-readable label that identifies the cloud service provider.
+
+
+<a id="nestedatt--backup_settings"></a>
+### Nested Schema for `backup_settings`
+
+Read-Only:
+
+- `enabled` (Boolean) Flag that indicates whether backups are performed for this flex cluster. Backup uses [TODO](TODO) for flex clusters.
+
+
+<a id="nestedatt--connection_strings"></a>
+### Nested Schema for `connection_strings`
+
+Read-Only:
+
+- `standard` (String) Public connection string that you can use to connect to this cluster. This connection string uses the mongodb:// protocol.
+- `standard_srv` (String) Public connection string that you can use to connect to this flex cluster. This connection string uses the `mongodb+srv://` protocol.
+
+# Import 
+You can import the Flex Cluster resource by using the Project ID and Flex Cluster name, in the format `PROJECT_ID-FLEX_CLUSTER_NAME`. For example:
+```
+$ terraform import mongodbatlas_flex_cluster.test 6117ac2fe2a3d04ed27a987v-yourFlexClusterName
+```
+
+For more information see: [MongoDB Atlas API - Flex Cluster](https://www.mongodb.com/docs/atlas/reference/api-resources-spec/#tag/Flex-Clusters/operation/createFlexcluster) Documentation.

examples/mongodbatlas_flex_cluster/README.md

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+# MongoDB Atlas Provider -- Atlas Flex Cluster
+This example creates one flex cluster in a project.
+
+Variables Required to be set:
+- `public_key`: Atlas public key
+- `private_key`: Atlas  private key
+- `project_id`: Project ID where flex cluster will be created
+- `cluster_name`: Name of flex cluster that will be created

examples/mongodbatlas_flex_cluster/main.tf

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+resource "mongodbatlas_flex_cluster" "example-cluster" {
+  project_id = var.project_id
+  name       = var.cluster_name
+  provider_settings = {
+    backing_provider_name = "AWS"
+    region_name           = "US_EAST_1"
+  }
+  termination_protection_enabled = true
+}
+
+data "mongodbatlas_flex_cluster" "example-cluster" {
+  project_id = var.project_id
+  name       = mongodbatlas_flex_cluster.example-cluster.name
+}
+
+data "mongodbatlas_flex_clusters" "example-clusters" {
+  project_id = var.project_id
+}
+
+output "mongodbatlas_flex_cluster" {
+  value = data.mongodbatlas_flex_cluster.example-cluster.name
+}
+
+output "mongodbatlas_flex_clusters_names" {
+  value = [for cluster in data.mongodbatlas_flex_clusters.example-clusters.results : cluster.name]
+}

examples/mongodbatlas_flex_cluster/provider.tf

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+provider "mongodbatlas" {
+  public_key  = var.public_key
+  private_key = var.private_key
+}