Unexpected error (StackExchange.Redis.RedisConnectionException) while execute function

Terraform Providers Azure
1

Hi,
I have a problem with the Redis Cache Private Endpoint, Private DNS in combination with a function.

Versions:

azurem: 2.78.0

Description:

The Terrafrom script generates all the required resources, but when the function starts, it cannot connect to the RedisCache via the private endpoint and the following error message appears.

Error Message:

Unexpected error (StackExchange.Redis.RedisConnectionException) while execute function: "No connection is active/available to service this operation; The remote certificate is invalid according to the validation procedure.ed; The remote certificate is invalid according to the validation procedure.

The terraform script looks like this:

provider "azurerm" {
  features {}
}

variable "address_space" {
  default = ["10.4.0.0/16"]
}

# VNET
resource "azurerm_resource_group" "rg" {
  name     = "vnet-rg"
  location = "westeurope"
  }

resource "azurerm_virtual_network" "vnet" {
  name                = "vnet"
  resource_group_name = azurerm_resource_group.rg.name
  location            = "westeurope"
  address_space       = var.address_space
  }

resource "azurerm_subnet" "rc_subnet" {
  name                                           = "rc-subnet"
  resource_group_name                            = azurerm_virtual_network.vnet.resource_group_name
  virtual_network_name                           = azurerm_virtual_network.vnet.name
  address_prefixes                               = [cidrsubnet(var.address_space[0], 8, 5)]
  enforce_private_link_endpoint_network_policies = true
  service_endpoints                              = ["Microsoft.Web"]
}

# Redis Cache
resource "azurerm_resource_group" "rg" {
  name     = "arc-rg"
  location = "westeurope"
  }

resource "azurerm_redis_cache" "rc" {
  name                          = "rc"
  resource_group_name           = azurerm_resource_group.rg.name
  location                      = azurerm_resource_group.rg.location
  capacity                      = 1
  family                        = "C"
  sku_name                      = "Basic"
  public_network_access_enabled = false
  enable_non_ssl_port           = false
  minimum_tls_version           = "1.2"
}

resource "azurerm_private_endpoint" "rc_endpoint" {
  name                = "rc-pe"
  location            = azurerm_resource_group.rg.location
  resource_group_name = azurerm_resource_group.rg.name
  subnet_id           = azurerm_subnet.rc_subnet.id

  private_service_connection {
    name                           = "rc-pe"
    is_manual_connection           = false
    private_connection_resource_id = azurerm_redis_cache.rc.id
    subresource_names              = ["redisCache"]
  }
}

# Private DNS
resource "azurerm_private_dns_zone" "rc_private_dns" {
  name                = "privatelink.redis.cache.windows.net"
  resource_group_name = azurerm_resource_group.rg.name
}

resource "azurerm_private_dns_zone_virtual_network_link" "vnet_link" {
  name                  = "vnet-link"
  resource_group_name   = azurerm_resource_group.rg.name
  private_dns_zone_name = azurerm_private_dns_zone.rc_private_dns.name
  virtual_network_id    = azurerm_virtual_network.vnet.id
}

resource "azurerm_private_dns_a_record" "rc_priv_dns" {
  name                = azurerm_redis_cache.rc.name
  zone_name           = azurerm_private_dns_zone.rc_private_dns.name
  resource_group_name = azurerm_resource_group.rg.name
  ttl                 = 300
  records             = [azurerm_private_endpoint.rc_endpoint.private_service_connection[0].private_ip_address]
}

resource "azurerm_function_app" "fa" {
  ...
  app_settings = {

    ...
    # Redis Cache
    REDIS_HOST = azurerm_private_dns_a_record.rc_priv_dns.fqdn
    REDIS_PORT = azurerm_redis_cache.rc.ssl_port
    REDIS_SSL  = "true"
    ...
    WEBSITES_ENABLE_APP_SERVICE_STORAGE = "true"
    WEBSITE_ENABLE_SYNC_UPDATE_SITE     = "true"
    WEBSITE_DNS_SERVER                  = "168.63.129.16"
    WEBSITE_VNET_ROUTE_ALL              = "1"
    WEBSITE_RUN_FROM_PACKAGE            = "1"
    ...
  }

I don’t know why the error occurs, maybe someone of you can help me here.

Thank you for your answers in advance.

Kind regards
Thorsten