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Plan a virtual network for Azure HDInsight

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This article provides background information on using Azure Virtual Networks (VNets) with Azure HDInsight. It also discusses design and implementation decisions that must be made before you can implement a virtual network for your HDInsight cluster. Once the planning phase is finished, you can proceed to Create virtual networks for Azure HDInsight clusters. For more information on HDInsight management IP addresses that are needed to properly configure network security groups (NSGs) and user-defined routes, see HDInsight management IP addresses.

Using an Azure Virtual Network enables the following scenarios:

  • Connecting to HDInsight directly from an on-premises network.
  • Connecting HDInsight to data stores in an Azure Virtual network.
  • Directly accessing Apache Hadoop services that aren't available publicly over the internet. For example, Apache Kafka APIs or the Apache HBase Java API.

Important

Creating an HDInsight cluster in a VNET will create several networking resources, such as NICs and load balancers. Do not delete or modify these networking resources, as they are needed for your cluster to function correctly with the VNET.

Planning

The following are the questions that you must answer when planning to install HDInsight in a virtual network:

  • Do you need to install HDInsight into an existing virtual network? Or are you creating a new network?

    If you're using an existing virtual network, you may need to modify the network configuration before you can install HDInsight. For more information, see the added HDInsight to an existing virtual network section.

  • Do you want to connect the virtual network containing HDInsight to another virtual network or your on-premises network?

    To easily work with resources across networks, you may need to create a custom DNS and configure DNS forwarding. For more information, see the connecting multiple networks section.

  • Do you want to restrict/redirect inbound or outbound traffic to HDInsight?

    HDInsight must have unrestricted communication with specific IP addresses in the Azure data center. There are also several ports that must be allowed through firewalls for client communication. For more information, see Control network traffic.

Add HDInsight to an existing virtual network

Use the steps in this section to discover how to add a new HDInsight to an existing Azure Virtual Network.

Note

  • You cannot add an existing HDInsight cluster into a virtual network.
  • The VNET and the cluster being created must be in the same subscription.

  1. Are you using a classic or Resource Manager deployment model for the virtual network?

    HDInsight 3.4 and greater requires a Resource Manager virtual network. Earlier versions of HDInsight required a classic virtual network.

    If your existing network is a classic virtual network, then you must create a Resource Manager virtual network and then connect the two. Connecting classic VNets to new VNets.

    Once joined, HDInsight installed in the Resource Manager network can interact with resources in the classic network.

  2. Do you use network security groups, user-defined routes, or Virtual Network Appliances to restrict traffic into or out of the virtual network?

    As a managed service, HDInsight requires unrestricted access to several IP addresses in the Azure data center. To allow communication with these IP addresses, update any existing network security groups or user-defined routes.

    HDInsight hosts multiple services, which use various ports. Don't block traffic to these ports. For a list of ports to allow through virtual appliance firewalls, see the Security section.

    To find your existing security configuration, use the following Azure PowerShell or Azure CLI commands:

    • Network security groups

      Replace RESOURCEGROUP with the name of the resource group that contains the virtual network, and then enter the command:

      Get-AzNetworkSecurityGroup -ResourceGroupName  "RESOURCEGROUP"

      az network nsg list --resource-group RESOURCEGROUP

      For more information, see Troubleshoot network security groups document.

      Important

      Network security group rules are applied in order based on rule priority. The first rule that matches the traffic pattern is applied, and no others are applied for that traffic. Order rules from most permissive to least permissive. For more information, see the Filter network traffic with network security groups document.

    • User-defined routes

      Replace RESOURCEGROUP with the name of the resource group that contains the virtual network, and then enter the command:

      Get-AzRouteTable -ResourceGroupName "RESOURCEGROUP"

      az network route-table list --resource-group RESOURCEGROUP

      For more information, see the Diagnose a virtual machine routing problem document.

  3. Create a HDInsight cluster and select the Azure Virtual Network during configuration. Use the steps in the following documents to understand the cluster creation process:

    Important

    Adding HDInsight to a virtual network is an optional configuration step. Be sure to select the virtual network when configuring the cluster.

Connecting multiple networks

The biggest challenge with a multi-network configuration is name resolution between the networks.

Azure provides name resolution for Azure services that are installed in a virtual network. This built-in name resolution allows HDInsight to connect to the following resources by using a fully qualified domain name (FQDN):

  • Any resource that is available on the internet. For example, microsoft.com, windowsupdate.com.

  • Any resource that is in the same Azure Virtual Network, by using the internal DNS name of the resource. For example, when using the default name resolution, the following are examples of internal DNS names assigned to HDInsight worker nodes:

    • <workername1>.0owcbllr5hze3hxdja3mqlrhhe.ex.internal.cloudapp.net

    • <workername2>.0owcbllr5hze3hxdja3mqlrhhe.ex.internal.cloudapp.net

      Both these nodes can communicate directly with each other, and other nodes in HDInsight, by using internal DNS names.

The default name resolution does not allow HDInsight to resolve the names of resources in networks that are joined to the virtual network. For example, it's common to join your on-premises network to the virtual network. With only the default name resolution, HDInsight can't access resources in the on-premises network by name. The opposite is also true, resources in your on-premises network can't access resources in the virtual network by name.

Warning

You must create the custom DNS server and configure the virtual network to use it before creating the HDInsight cluster.

To enable name resolution between the virtual network and resources in joined networks, you must perform the following actions:

  1. Create a custom DNS server in the Azure Virtual Network where you plan to install HDInsight.

  2. Configure the virtual network to use the custom DNS server.

  3. Find the Azure assigned DNS suffix for your virtual network. This value is similar to 0owcbllr5hze3hxdja3mqlrhhe.ex.internal.cloudapp.net. For information on finding the DNS suffix, see the Example: Custom DNS section.

  4. Configure forwarding between the DNS servers. The configuration depends on the type of remote network.

    • If the remote network is an on-premises network, configure DNS as follows:

      • Custom DNS (in the virtual network):

        • Forward requests for the DNS suffix of the virtual network to the Azure recursive resolver (168.63.129.16). Azure handles requests for resources in the virtual network

        • Forward all other requests to the on-premises DNS server. The on-premises DNS handles all other name resolution requests, even requests for internet resources such as Microsoft.com.

      • On-premises DNS: Forward requests for the virtual network DNS suffix to the custom DNS server. The custom DNS server then forwards to the Azure recursive resolver.

        This configuration routes requests for fully qualified domain names that contain the DNS suffix of the virtual network to the custom DNS server. All other requests (even for public internet addresses) are handled by the on-premises DNS server.

    • If the remote network is another Azure Virtual Network, configure DNS as follows:

      • Custom DNS (in each virtual network):

        • Requests for the DNS suffix of the virtual networks are forwarded to the custom DNS servers. The DNS in each virtual network is responsible for resolving resources within its network.

        • Forward all other requests to the Azure recursive resolver. The recursive resolver is responsible for resolving local and internet resources.

        The DNS server for each network forwards requests to the other, based on DNS suffix. Other requests are resolved using the Azure recursive resolver.

      For an example of each configuration, see the Example: Custom DNS section.

For more information, see the Name Resolution for VMs and Role Instances document.

Directly connect to Apache Hadoop services

You can connect to the cluster at https://CLUSTERNAME.azurehdinsight.net. This address uses a public IP, which may not be reachable if you have used NSGs to restrict incoming traffic from the internet. Additionally, when you deploy the cluster in a virtual network you can access it using the private endpoint https://CLUSTERNAME-int.azurehdinsight.net. This endpoint resolves to a private IP inside the virtual network for cluster access.

To connect to Apache Ambari and other web pages through the virtual network, use the following steps:

  1. To discover the internal fully qualified domain names (FQDN) of the HDInsight cluster nodes, use one of the following methods:

    Replace RESOURCEGROUP with the name of the resource group that contains the virtual network, and then enter the command:

    $clusterNICs = Get-AzNetworkInterface -ResourceGroupName "RESOURCEGROUP" | where-object {$_.Name -like "*node*"}

$nodes = @()
foreach($nic in $clusterNICs) {
    $node = new-object System.Object
    $node | add-member -MemberType NoteProperty -name "Type" -value $nic.Name.Split('-')[1]
    $node | add-member -MemberType NoteProperty -name "InternalIP" -value $nic.IpConfigurations.PrivateIpAddress
    $node | add-member -MemberType NoteProperty -name "InternalFQDN" -value $nic.DnsSettings.InternalFqdn
    $nodes += $node
}
$nodes | sort-object Type

    az network nic list --resource-group RESOURCEGROUP --output table --query "[?contains(name, 'node')].{NICname:name,InternalIP:ipConfigurations[0].privateIpAddress,InternalFQDN:dnsSettings.internalFqdn}"

    In the list of nodes returned, find the FQDN for the head nodes and use the FQDNs to connect to Ambari and other web services. For example, use http://<headnode-fqdn>:8080 to access Ambari.

    Important

    Some services hosted on the head nodes are only active on one node at a time. If you try accessing a service on one head node and it returns a 404 error, switch to the other head node.

  2. To determine the node and port that a service is available on, see the Ports used by Hadoop services on HDInsight document.

Load balancing

When you create a HDInsight cluster, several load balancers are created as well. Due to the retirement of the basic load balancer, the type of load balancers is at the standard SKU level, which has certain constraints. Inbound flows to the standard load balancers are closed unless allowed  by a network security group. You may need to bond a network security to your subnet and configure the network security rules.

There are several outbound connectivity methods enabled for the standard load balancer. It’s worth noting that the default outbound access will be retired soon. If a NAT gateway is adopted to provide outbound network access, the subnet is not capable with the basic load balancer. If you intend to bond a NAT gateway to a subnet, there should be no basic load balancer existed in this subnet. With the NAT gateway as the outbound access method, a newly created HDInsight cluster can't share the same subnet with previously created HDInsight clusters with basic load balancers.

Another constraint is that the HDInsight load balancers shouldn't be deleted or modified. Any changes to the load balancer rules will get overwritten during certain maintenance events such as certificate renewals. If the load balancers are modified and it affects the cluster functionality, you may need to recreate the cluster.

Next steps