Configure custom DNS settings using dnsmasq

Learn how to configure custom DNS settings using dnsmasq.

Written by brian.sears

Last published at: May 10th, 2023

dnsmasq is a tool for installing and configuring DNS routing rules for cluster nodes. You can use it to set up routing between your Databricks environment and your on-premise network.

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Warning

If you use your own DNS server and it goes down, you will experience an outage and will not be able to create clusters.

Use the following cluster-scoped init script to configure dnsmasq for a cluster node.

  1. Use netcat (nc) to test connectivity from the notebook environment to your on-premise network.
    nc -vz <on-premise-ip> 53
  2. Create the base directory you want to store the init script in if it does not already exist.
    dbutils.fs.mkdirs("dbfs:/databricks/<init-script-folder>/")
  3. Create the script.

    AWS Scala example

    dbutils.fs.put("/databricks/<init-script-folder>/dns-masq.sh","""
    #!/bin/bash
    ########################################
    Configure on-prem dns access.
    ########################################
    
    sudo apt-get update -y
    sudo apt-get install dnsmasq -y --force-yes
    
    ## Add dns entries for internal your-company.net name servers
    echo server=/databricks.net/<dns-server-ip> | sudo tee --append /etc/dnsmasq.conf
    
    ## Find the default DNS settings for the EC2 instance and use them as the default DNS route
    
    ec2_dns=cat /etc/resolv.conf | grep "nameserver"; | cut -d' ' -f 2
    echo "Old dns in resolv.conf $ec2_dns"
    
    echo "server=$ec2_dns" | sudo tee --append /etc/dnsmasq.conf
    
    ## configure resolv.conf to point to dnsmasq service instead of static resolv.conf file
    mv /etc/resolv.conf /etc/resolv.conf.orig
    echo nameserver 127.0.0.1 | sudo tee --append /etc/resolv.conf
    sudo systemctl disable --now systemd-resolved
    sudo systemctl enable --now dnsmasq
    """, true)
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    Azure Scala example

    dbutils.fs.put("/databricks/<init-script-folder>/dns-masq.sh","""
    #!/bin/bash
    sudo apt-get update -y
    sudo apt-get install dnsmasq -y --force-yes
    
    ## Add dns entries for internal nameservers
    echo server=/databricks.net/<dns-server-ip> | sudo tee --append /etc/dnsmasq.conf
       
    ## Find the default DNS settings for the instance and use them as the default DNS route
    azvm_dns=cat /etc/resolv.conf | grep "nameserver"; | cut -d' ' -f 2
    echo "Old dns in resolv.conf $azvm_dns"
    echo "server=$azvm_dns" | sudo tee --append /etc/dnsmasq.conf
        
    ## configure resolv.conf to point to dnsmasq service instead of static resolv.conf file
    mv /etc/resolv.conf /etc/resolv.conf.orig
    echo nameserver 127.0.0.1 | sudo tee --append /etc/resolv.conf
    sudo systemctl disable --now systemd-resolved
    sudo systemctl enable --now dnsmasq
    """, true)
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  4. Check that the script exists.
    display(dbutils.fs.ls("dbfs:/databricks/<init-script-folder>/dns-masq.sh"))
  5. Configure the init script that you just created as a cluster-scoped init script. You will need the full path to the location of the script (dbfs:/databricks/<init-script-folder>/dns-masq.sh).
  6. Launch a zero-node cluster to confirm that you can create clusters.
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