dns resolving not working in azure environement

Arne Hebbrecht 0

hello, so i have been looking for a solution for a couple off days now. i' am deploying a frontend (dockerized vue.js) and a backend (dockerized asp.net application). both are inside a subnet (containers) inside a vnet. there is a application gateway with a public ip address. the application loadbalancer backendpool is connected to the fqdn of the frontend. there is a private dns zone that redirects the traffic to the loadbalancer static ip of the environnement.

Now the problem i am having is i can curl with the loadbalanced link to the backend example : curl https://backend.example.com this returns a hello world for testing but now when i connect to the frontend true the public ip and do the same (using axios doing the fetch server side and not in the browser) i get that the dns name is not able to be resolved

what could the problem be ?

ChaitanyaNaykodi-MSFT 22,941 Reputation points Microsoft Employee

2024-03-25T22:53:56.13+00:00
@Arne Hebbrecht

Thank you for reaching out.

It will help if you could provide the information below to troubleshoot this issue.

A rough network diagram of your set-up with expected traffic flow and connections.

A screenshot of the Application Gateway's listener configuration, backend settings and backend health details.

Thank you!

Arne Hebbrecht 0

So this is the basic setup of the network.

User's image

so when i go from the client pc to the frontend container this works (i have a private dns zone that has recorord that point from the fqdn --> static ip of the container environement (the environement is ran true in my own vnet and is inside a subnet now from my understanding the frontend and backend should be able to communciate with eachother tru the internal loadbalancer of the environement for example i would curl from https://frontend.environment.test to https://backend.environement.test now this gives me a hello world (backend is a api )

first thing i tried was to to a fetch with and withouth axios beacuse i didnt know if the fecth happend in the browser or on the server (neeeds to be on the server for the dns resolving to work i think new to frontend applications)

second was also adding the backend fqdn to the private dns zon and als pointing it to the static ip of the container environnement

but after al this the weird part is that the curl gives me the expected answer but the fecth doesn't resolve the dns

here are also the cal from the frontend the fqdn are not correct i know just examples

User's image

if further explanition is needed ill be ready to answer if needed i also have the terraform code for this project (takes about half an hour to setup)

and the requested screenshots listener

User's image

backend settings

User's image

backend health

User's image

also the terraform script of the application laodblancer if you want it

resource "azurerm_application_gateway" "res-3" {
  enable_http2        = true
  location            = var.location
  name                = "Container-apps-gateway"
  resource_group_name = var.resource_group_name
  zones               = ["1", "2", "3"]
  backend_address_pool {
    fqdns = ["${var.appName}.${azurerm_container_app_environment.res-2.default_domain}"] 
    name  = "agw-backend-pool"
  }
  backend_http_settings {
    cookie_based_affinity               = "Disabled"
    name                                = "agw-backend-setting"
    pick_host_name_from_backend_address = true
    port                                = 443
    protocol                            = "Https"
    request_timeout                     = 20
  }
  frontend_ip_configuration {
    name                            = "appGwPublicFrontendIpIPv4"
    private_link_configuration_name = "agw-private-link"
    public_ip_address_id            = azurerm_public_ip.res-6.id
  }
  frontend_port {
    name = "port_80"
    port = 80
  }
  gateway_ip_configuration {
    name      = "appGatewayIpConfig"
    subnet_id = azurerm_subnet.res-9.id
  }
  http_listener {
    frontend_ip_configuration_name = "appGwPublicFrontendIpIPv4"
    frontend_port_name             = "port_80"
    name                           = "agw-listener"
    protocol                       = "Http"
  }
  private_link_configuration {
    name = "agw-private-link"
    ip_configuration {
      name                          = "privateLinkIpConfig1"
      primary                       = false
      private_ip_address_allocation = "Dynamic"
      subnet_id                     = azurerm_subnet.res-8.id
    }
  }
  request_routing_rule {
    backend_address_pool_name  = "agw-backend-pool"
    backend_http_settings_name = "agw-backend-setting"
    http_listener_name         = "agw-listener"
    name                       = "agw-routing-rule"
    priority                   = 1
    rule_type                  = "Basic"
  }
  sku {
    capacity = 1
    name     = "Standard_v2"
    tier     = "Standard_v2"
  }
  depends_on = [
    azurerm_public_ip.res-6,
    azurerm_private_dns_zone.res-4,
    azurerm_container_app_environment.res-2,
    azurerm_container_app.res-1
  ]
}

resource "azurerm_public_ip" "res-6" {
  allocation_method   = "Static"
  location            = var.location
  name                = "frontend-ip"
  resource_group_name = var.resource_group_name
  sku                 = "Standard"
  zones               = ["1", "2", "3"]
  depends_on = [
    azurerm_private_dns_zone.res-4,
    azurerm_container_app_environment.res-2,
    azurerm_container_app.res-1
  ]  
}

ChaitanyaNaykodi-MSFT 22,941 Reputation points Microsoft Employee

2024-04-10T03:35:48.4233333+00:00

@Arne Hebbrecht

Apologies for the delay in getting back to you here.

In order to further troubleshoot this issue, I can offer you a one-time free support ticket in order to help resolve the issue. Please refer to my private message here for additional details.

1 answer

Glen Rego 75 Reputation points Microsoft Employee

2024-03-25T23:47:31.73+00:00

@Arne Hebbrecht

If the Application Gateway listener is configured as a multisite that listens on a specific hostname, attempting to access the DNS name of the public address will not function. Providing additional details about the configuration would be greatly beneficial in gaining further insights.
Please sign in to rate this answer.
Arne Hebbrecht 0 Reputation points

2024-03-26T12:38:01.4866667+00:00

So this is the basic setup of the network.

so when i go from the client pc to the frontend container this works (i have a private dns zone that has recorord that point from the fqdn --> static ip of the container environement (the environement is ran true in my own vnet and is inside a subnet now from my understanding the frontend and backend should be able to communciate with eachother tru the internal loadbalancer of the environement for example i would curl from https://frontend.environment.test to https://backend.environement.test now this gives me a hello world (backend is a api )

first thing i tried was to to a fetch with and withouth axios beacuse i didnt know if the fecth happend in the browser or on the server (neeeds to be on the server for the dns resolving to work i think new to frontend applications)

second was also adding the backend fqdn to the private dns zon and als pointing it to the static ip of the container environnement

but after al this the weird part is that the curl gives me the expected answer but the fecth doesn't resolve the dns

here are also the cal from the frontend the fqdn are not correct i know just examples

if further explanition is needed ill be ready to answer if needed i also have the terraform code for this project (takes about half an hour to setup)
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