[DTOSS-12318] - feat(iac): add Azure Bastion module with public IP and diagnostic settings

infrastructure/modules/bastion/README.md

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+# bastion
+
+Deploy an [Azure Bastion host](https://learn.microsoft.com/en-us/azure/bastion/bastion-overview) with a dedicated public IP address and diagnostic settings. Integrates with the [subnet module](../subnet/) and [log-analytics-workspace module](../log-analytics-workspace/).
+
+## Terraform documentation
+
+For the list of inputs, outputs, resources... check the [terraform module documentation](tfdocs.md).
+
+## Prerequisites
+
+Azure Bastion requires a dedicated subnet named exactly `AzureBastionSubnet` with a minimum `/26` prefix. Use the [subnet module](../subnet/) to create it with the required NSG rules:
+
+```hcl
+module "subnet_bastion" {
+  source = "../subnet"
+
+  name                = "AzureBastionSubnet"
+  resource_group_name = azurerm_resource_group.main.name
+  vnet_name           = module.vnet.name
+  address_prefixes    = [cidrsubnet(var.vnet_address_space, 10, 0)]
+  location            = var.region
+  create_nsg          = true
+  network_security_group_name      = "nsg-bastion-${var.env_config}-uks"
+  network_security_group_nsg_rules = local.bastion_nsg_rules
+
+  log_analytics_workspace_id                                     = module.log_analytics_workspace.id
+  monitor_diagnostic_setting_network_security_group_enabled_logs = []
+}
+```
+
+See [Azure Bastion NSG requirements](https://learn.microsoft.com/en-us/azure/bastion/bastion-nsg) for the required inbound and outbound rules.
+
+## Usage
+
+Deploy a Standard Bastion host with audit logging:
+
+```hcl
+module "bastion" {
+  source = "../../../dtos-devops-templates/infrastructure/modules/bastion"
+
+  name                = "bas-myapp-dev-uks"
+  public_ip_name      = "pip-bastion-myapp-dev-uks"
+  resource_group_name = azurerm_resource_group.main.name
+  location            = "uksouth"
+  sku                 = "Standard"
+  subnet_id           = module.subnet_bastion.id
+
+  log_analytics_workspace_id                      = module.log_analytics_workspace.id
+  monitor_diagnostic_setting_bastion_enabled_logs = ["BastionAuditLogs"]
+  monitor_diagnostic_setting_bastion_metrics      = ["AllMetrics"]
+}
+```
+
+## SKU selection
+
+| SKU | Scale units | Native client | File copy | IP connect | Session recording | Public IP required |
+|-----|-------------|---------------|-----------|------------|-------------------|--------------------|
+| Basic | Fixed (2) | No | No | No | No | Yes |
+| Standard | 2–50 | Yes | Yes | Yes | No | Yes |
+| Premium | 2–50 | Yes | Yes | Yes | Yes | Yes |
+
+- **Standard** is recommended for most production workloads. It supports native client connections, host scaling, and all advanced features.
+- **Premium** adds session recording for compliance requirements and a private-only deployment option (no public IP).
+- **Basic** provides a fixed-capacity dedicated deployment at lower cost. Advanced features are not available.
+- **Developer** SKU is not supported by this module — it uses shared infrastructure and does not require a public IP or dedicated subnet.
+
+## Zone redundancy (recommended for production)
+
+By default the public IP is deployed with no availability zone pinning. For production, pass `zones = ["1", "2", "3"]` to make the public IP zone-redundant:
+
+```hcl
+module "bastion" {
+  ...
+  zones = ["1", "2", "3"]
+}
+```
+
+Zone-redundant public IPs are available in UK South at no additional cost. See [Reliability in Azure Bastion](https://learn.microsoft.com/en-us/azure/reliability/reliability-bastion) for supported regions.
+
+## Standard/Premium features
+
+The following features are disabled by default and require Standard SKU or higher:
+
+**Native client / tunneling** — enables SSH and RDP connections via the Azure CLI (`az network bastion ssh`, `az network bastion rdp`) instead of the browser-based client. Recommended for operations teams:
+
+```hcl
+module "bastion" {
+  ...
+  tunneling_enabled = true
+}
+```
+
+**IP connect** — allows connecting to VMs using their private IP address rather than requiring them to be in the same virtual network:
+
+```hcl
+module "bastion" {
+  ...
+  ip_connect_enabled = true
+}
+```
+
+**File copy** — enables file transfer between the local machine and target VMs via native client connections:
+
+```hcl
+module "bastion" {
+  ...
+  file_copy_enabled = true
+  tunneling_enabled = true  # file copy requires native client
+}
+```
+
+## Scaling
+
+Each scale unit supports approximately 20 concurrent RDP sessions or 40 concurrent SSH sessions. The default of 2 units (40 RDP / 80 SSH) is sufficient for most environments. Increase `scale_units` for larger deployments:
+
+```hcl
+module "bastion" {
+  ...
+  scale_units = 5  # ~100 concurrent RDP / ~200 concurrent SSH
+}
+```
+
+`scale_units` is only configurable for Standard and Premium SKUs. Basic is fixed at 2 units.
+
+## Diagnostic logs
+
+The module creates a diagnostic setting targeting the provided Log Analytics workspace. The only available log category for Azure Bastion is `BastionAuditLogs`, which records user connections, source IPs, session metadata, and audit trail information:
+
+```hcl
+module "bastion" {
+  ...
+  monitor_diagnostic_setting_bastion_enabled_logs = ["BastionAuditLogs"]
+  monitor_diagnostic_setting_bastion_metrics      = ["AllMetrics"]
+}
+```

infrastructure/modules/bastion/main.tf

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+module "pip" {
+  source = "../public-ip"
+
+  name                = var.public_ip_name
+  resource_group_name = var.resource_group_name
+  location            = var.location
+  allocation_method   = "Static"
+  sku                 = "Standard"
+  zones               = var.zones
+
+  tags = var.tags
+}
+
+resource "azurerm_bastion_host" "bastion" {
+  name                = var.name
+  location            = var.location
+  resource_group_name = var.resource_group_name
+  sku                 = var.sku
+
+  copy_paste_enabled     = var.copy_paste_enabled
+  file_copy_enabled      = var.file_copy_enabled
+  ip_connect_enabled     = var.ip_connect_enabled
+  tunneling_enabled      = var.tunneling_enabled
+  shareable_link_enabled = var.shareable_link_enabled
+  scale_units            = var.scale_units
+
+  ip_configuration {
+    name                 = "configuration"
+    subnet_id            = var.subnet_id
+    public_ip_address_id = module.pip.id
+  }
+
+  tags = var.tags
+}
+
+module "diagnostic_settings" {
+  source = "../diagnostic-settings"
+
+  name                       = "${var.name}-diagnostic-setting"
+  target_resource_id         = azurerm_bastion_host.bastion.id
+  log_analytics_workspace_id = var.log_analytics_workspace_id
+  enabled_log                = var.monitor_diagnostic_setting_bastion_enabled_logs
+  enabled_metric             = var.monitor_diagnostic_setting_bastion_metrics
+}

infrastructure/modules/bastion/outputs.tf

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+output "id" {
+  description = "The ID of the Bastion host."
+  value       = azurerm_bastion_host.bastion.id
+}
+
+output "name" {
+  description = "The name of the Bastion host."
+  value       = azurerm_bastion_host.bastion.name
+}
+
+output "dns_name" {
+  description = "The FQDN of the Bastion host."
+  value       = azurerm_bastion_host.bastion.dns_name
+}
+
+output "public_ip_address" {
+  description = "The public IP address associated with the Bastion host."
+  value       = module.pip.ip_address
+}

infrastructure/modules/bastion/tfdocs.md

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+# Module documentation
+
+## Required Inputs
+
+The following input variables are required:
+
+### <a name="input_log_analytics_workspace_id"></a> [log\_analytics\_workspace\_id](#input\_log\_analytics\_workspace\_id)
+
+Description: The ID of the Log Analytics workspace to send diagnostic logs to.
+
+Type: `string`
+
+### <a name="input_monitor_diagnostic_setting_bastion_enabled_logs"></a> [monitor\_diagnostic\_setting\_bastion\_enabled\_logs](#input\_monitor\_diagnostic\_setting\_bastion\_enabled\_logs)
+
+Description: List of log categories to enable for the Bastion diagnostic setting (e.g. ["BastionAuditLogs"]).
+
+Type: `list(string)`
+
+### <a name="input_monitor_diagnostic_setting_bastion_metrics"></a> [monitor\_diagnostic\_setting\_bastion\_metrics](#input\_monitor\_diagnostic\_setting\_bastion\_metrics)
+
+Description: List of metric categories to enable for the Bastion diagnostic setting (e.g. ["AllMetrics"]).
+
+Type: `list(string)`
+
+### <a name="input_name"></a> [name](#input\_name)
+
+Description: The name of the Azure Bastion host.
+
+Type: `string`
+
+### <a name="input_public_ip_name"></a> [public\_ip\_name](#input\_public\_ip\_name)
+
+Description: The name of the public IP address resource created for the Bastion host.
+
+Type: `string`
+
+### <a name="input_resource_group_name"></a> [resource\_group\_name](#input\_resource\_group\_name)
+
+Description: The name of the resource group in which to create the Bastion host.
+
+Type: `string`
+
+### <a name="input_subnet_id"></a> [subnet\_id](#input\_subnet\_id)
+
+Description: The ID of the AzureBastionSubnet in which the Bastion host will be deployed.
+
+Type: `string`
+
+## Optional Inputs
+
+The following input variables are optional (have default values):
+
+### <a name="input_copy_paste_enabled"></a> [copy\_paste\_enabled](#input\_copy\_paste\_enabled)
+
+Description: Is copy/paste feature enabled for the Bastion host.
+
+Type: `bool`
+
+Default: `true`
+
+### <a name="input_file_copy_enabled"></a> [file\_copy\_enabled](#input\_file\_copy\_enabled)
+
+Description: Is file copy feature enabled for the Bastion host. Requires Standard SKU or higher.
+
+Type: `bool`
+
+Default: `false`
+
+### <a name="input_ip_connect_enabled"></a> [ip\_connect\_enabled](#input\_ip\_connect\_enabled)
+
+Description: Is IP connect feature enabled for the Bastion host. Requires Standard SKU or higher.
+
+Type: `bool`
+
+Default: `false`
+
+### <a name="input_location"></a> [location](#input\_location)
+
+Description: The location/region where the Bastion host will be created.
+
+Type: `string`
+
+Default: `"uksouth"`
+
+### <a name="input_scale_units"></a> [scale\_units](#input\_scale\_units)
+
+Description: The number of scale units for the Bastion host. Each unit supports ~20 concurrent RDP / ~40 concurrent SSH sessions. Must be between 2 and 50 for Standard/Premium SKU; Basic is fixed at 2.
+
+Type: `number`
+
+Default: `2`
+
+### <a name="input_shareable_link_enabled"></a> [shareable\_link\_enabled](#input\_shareable\_link\_enabled)
+
+Description: Is shareable link feature enabled for the Bastion host. Requires Standard SKU or higher.
+
+Type: `bool`
+
+Default: `false`
+
+### <a name="input_sku"></a> [sku](#input\_sku)
+
+Description: The SKU tier of the Bastion host. Possible values are Basic, Standard, and Premium. Standard is recommended for most production workloads; Premium adds session recording and private-only deployment. Developer SKU is not supported by this module as it does not use a public IP or dedicated subnet.
+
+Type: `string`
+
+Default: `"Standard"`
+
+### <a name="input_tags"></a> [tags](#input\_tags)
+
+Description: A mapping of tags to assign to the resource.
+
+Type: `map(string)`
+
+Default: `{}`
+
+### <a name="input_tunneling_enabled"></a> [tunneling\_enabled](#input\_tunneling\_enabled)
+
+Description: Is tunneling (native client support) feature enabled for the Bastion host. Enables native SSH/RDP client connections via az network bastion ssh/rdp. Recommended for Standard SKU or higher.
+
+Type: `bool`
+
+Default: `false`
+
+### <a name="input_zones"></a> [zones](#input\_zones)
+
+Description: Availability zones for the public IP address. Use ["1", "2", "3"] for zone-redundant deployment, which is recommended for production environments. An empty list deploys with no zone redundancy.
+
+Type: `list(string)`
+
+Default: `[]`
+## Modules
+
+The following Modules are called:
+
+### <a name="module_diagnostic_settings"></a> [diagnostic\_settings](#module\_diagnostic\_settings)
+
+Source: ../diagnostic-settings
+
+Version:
+
+### <a name="module_pip"></a> [pip](#module\_pip)
+
+Source: ../public-ip
+
+Version:
+## Outputs
+
+The following outputs are exported:
+
+### <a name="output_dns_name"></a> [dns\_name](#output\_dns\_name)
+
+Description: The FQDN of the Bastion host.
+
+### <a name="output_id"></a> [id](#output\_id)
+
+Description: The ID of the Bastion host.
+
+### <a name="output_name"></a> [name](#output\_name)
+
+Description: The name of the Bastion host.
+
+### <a name="output_public_ip_address"></a> [public\_ip\_address](#output\_public\_ip\_address)
+
+Description: The public IP address associated with the Bastion host.
+## Resources
+
+The following resources are used by this module:
+
+- [azurerm_bastion_host.bastion](https://registry.terraform.io/providers/hashicorp/azurerm/latest/docs/resources/bastion_host) (resource)