Aleksandar Stefanov

Aleksandar Stefanov

Azure Cloud Architect

Azure Container Instances in VNET with custom DNS

2 minute read

Azure Container Instances (ACI) enables you to run containers on-demand without managing or thinking about the infrastructure below. In summary, it is a serverless container runtime offering. It supports both Linux and Windows containers.

You can deploy Linux containers into an Azure virtual network, which will make them reachable from your networks. If you are using custom DNS resolvers in the VNET where you plan to deploy your ACI, the containers will not inherit that configuration. By default, they will use the Azure DNS service with the virtual IP address of 168.63.129.16.

To specify your custom DNS servers, you need to use YAML file for the deployments. The following is an example of the content of such a file:

apiVersion: '2021-07-01'
location: westeurope
name: customdns
properties:
  containers:
  - name: alpine01
    properties:
      image: alpine
      command:
      - tail
      - -f
      - /dev/null
      resources:
        requests:
          cpu: 1
          memoryInGb: 1.5
      ports:
      - port: 80
  dnsConfig:
    nameServers:
      - <YOUR DNS SERVER>
      - <YOUR DNS SERVER>
  subnetIds: # Subnet to deploy the container group into
    - id: <RESOURCE ID OF YOUR SUBNET - in a format /subscriptions/<subscription_id>/resourceGroups/<resource_group_name>/providers/Microsoft.Network/virtualNetworks/<virtual_network_name>/subnets/<subnet_name>>
      name: <SUBNET NAME>
  ipAddress:
    type: Private
    ports:
    - protocol: tcp
      port: '80'
  osType: Linux  
type: Microsoft.ContainerInstance/containerGroups

You then create a Container Instance using the yaml file:

az container create -g <RESOURCE GROUP NAME> -f containerGroup.yml

To verify the DNS configuration, connect to the console of your container, and check the content of the /etc/resolv.conf file:

cat /etc/resolv.conf

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