Setup a custom dynamic DNS for instances in an OpenStack cloud

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The “ddns” set of scripts allow one to create a dynamic DNS for OpenStack cloud instances. Cloud providers may default to using unique and long hostnames, like instance.ff0f61549f3c4c6cb72a64f16572a524.compute.subdomain.domain.com.

One might prefer to use easier to remember hostnames, like instance.subdomain.domain.com. The “ddns” set of scripts allows one to use simpler hostnames. A cloud admin can use these scripts to to set up a hostname scheme and dynamic DNS for users in an OpenStack cloud.

This solution includes the following:

1. setup file - setup_ddns.sh

2. configuration file - ddns_config.yaml

3. ddns.sh executable - this main script will be autogenerated by setup_ddns.sh

4. python routines that are executed by scripts: ddns.py, gen_bind_files.py, gen_ddns_sh.py and ddns_common.py

5. templates directory, including templates for generating the following: ddns.sh, named.conf, forward and reverse zone files

1. Deploy a Centos/RHEL 6.5 instance for the DNS. It should be sufficient to choose a smaller flavor like “n1.small”.

2. Add a Floating IP

3. Setup security group rules for the DNS instance. The following ports should be open: TCP 22 (SSH), TCP 53 and UDP 53 (for DNS).

4. If the iptables service is on, it may be easiest to turn it off

5. Ensure that the OpenStack CLI clients are installed

Install the bind and bind-utils packages if they have not already been installed. Note that bind sets up the DNS server and bind-utils has the nsupdate tools.

[centos@ddns ~]$ sudo yum update -y
[centos@ddns ~]$ sudo yum install -y bind bind-utils

Using the Admin’s credentials will allow the “DDNS “ scripts to see instances across projects. If openrc.sh prompts for a password, remove the prompt and add the password in the file. Including the password in the file will be required for the scripts to run automatically. Below is an example of how to test the openrc.sh file using the OpenStack CLI.

[centos@ddns ~]$ source openrc.sh 
[centos@ddns ~]$ nova list

For example,

[centos@ddns ~]$ unzip /tmp/ddns.zip

The “ddns_config.yaml” file has all of the configuration parameters that will be used to configure BIND and the “DDNS” scripts. Edit this file and input customized information. Then save the file. It is important to make sure there are no errors, like no overlapping IP ranges in this file. Note that all fields can take only one value with the exception of “forwarders” and “ip_ranges”. Multiple forwarders and IP address ranges can be included. The IP address ranges are for both the fixed and floating OpenStack networks. These scripts require that the ranges be on octet boundaries, e.g. /24, /16 or /8. Here is an already filled in sample of the required fields.

domain_name: cloud.myuniverse.org
dns_shortname: bigbang
dns_fixed_ip: 10.130.52.121
dns_floating_ip: 10.130.56.248
forwarders:
  - 10.130.0.1
ip_ranges:
  - 10.130.52.0/24

setup_ddns.sh creates configuration files for the DNS updates as well as configuration files for BIND. It then moves the BIND files to the appropriate directories and restarts the DNS (“named”) service. Feel free to view the script to see what it does. Run this script using “sudo”.

[centos@ddns ~]$ sudo ./setup_ddns.sh

Now the main executable script, ddns.sh, has been created. It will use the OpenStack APIs to query instances and then update the DNS appropriately. Run the script.

[centos@ddns ~]$ ./ddns.sh

The following example shows how to setup cron to call ddns.sh every minute.

[centos@ddns ~]$ crontab –e  

Once in the file, add “ * * * * * ”. To monitor if the cron is working monitor /var/log/messages with “tail –f /var/log/messages”.

###8. Test the DNS Server

Use ping and dig or nslookup to test the DNS server

An instance needs to be configured to resolve using the new DNS. The easiest way to do this is to configure the image(s). In the image, change /etc/resolv.conf and /etc/sysconfig/network-scripts/ifcfg-eth0 as described below. These changes can also be done for an individual instance.

First, change the contents of resolv.conf as follows. The “nameserver_ip” can be either the fixed or floating IP of the DNS instance.

search <domain_name>
nameserver <nameserver_ip>

For example, type:

echo "PEERDNS=no" >> /etc/sysconfig/network-scripts/ifcfg-eth0