Build your own 11.2 RAC system-part II: DNS & DHCP for GNS

UPDATE 221103: Oracle 11.2 is effectively out of support, this article is now archived and shouldn’t be referred to.

Wow, I managed to cram 4 acronyms into the subject line, not bad for a Friday! The reason of this post is simple: I want to get Grid Naming Service (GNS) up and running on my 11.2 RAC system, after all it’s one of the major new features for 11.2. It required me to get acquainted with administering a Domain Name Service (DNS) server. In addition to a DNS system I also had to set up a system serving IP addresses using the Dynamic Host Configuration Protocol (DHCP). Getting GNS to work with RAC is purely optional though and the configuration files shown below are for lab-use only!

To use GNS with RAC 11.2 (part of Grid Plug And Play) we need DHCP and DNS, so let’s tackle them one by one in the lab. This article is based on Oracle Linux 5.2 and Oracle Real Application Cluster 11.2. A dedicated VM was created to serve DHCP and DNS requests, its IP is 192.168.1.82.

DHCP

DHCP is another one of those services the linux sys admin normally provides; DHCP is short for Dynamic Host Configuration Protocol. There has to be a package which provides the service, and sure enough this is called  dhcp. The dhcp client normally is installed already which makes it easy to avoid confusion.

Let’s start by installing the dhcp server (your version is most likely newer than the base release)

# rpm -ihv dhcp-3.0.5-13.el5

Documentation is a great way to get started so I looked up a sample configuration file for my network. GNS will require to assign IP addresses on the public network so I came up with the following configuration in /etc/dhcpd.conf

ddns-update-style interim; 
ignore client-updates; 

subnet 192.168.1.0 netmask 255.255.255.0 { 
    option subnet-mask 255.255.255.0; 
    option domain-name "the-playground.de"; 
    range 192.168.1.100 192.168.1.254; 
    default-lease-time 21600; 
    max-lease-time 43200; 
}

A simple service dhcpd start as root started the service. Easy enough, now for DNS.

Configuring DNS for GNS

Please refer to part I of the series for an (albeit very brief) introduction to DNS. The difference now is that we have to delegate the subdomain to GNS,  which involves a little bit of work on the DNS server. Also, we need to put a virtual IP address for GNS into DNS, but that address must not be in use – the so-called GNS glue record.

Bind9 as shipped with RHEL 5.2 is again in use. Remember that the DNS server resides on auxOEL5.the-playground.de with an IP address of 192.168.1.82. I’m using 192.168.1.92 as the GNS glue record, and the subdomain used for GNS is rac.the-playground.de. Final reminder that this isn’t a production-grade configuration: a lot of security features normally found in real DNS servers is left out of the configuration to keep it simple. Let’s start again by installing bind:

# rpm -ihv bind-9.3.4-6.P1.el5.x86_64.rpm

With the software and its dependencies in place the next step is to create the configuration. This is a rather complex topics and many books have been written about bind 9. Getting into every detail of the configuration however is out of scope of this article, please refer to the documentation if you like to better understand what each option in the following files implies in more detail.

File: /etc/named.conf

options
{
	/* make named use port 53 for the source of all queries, to allow
         * firewalls to block all ports except 53:
         */
	query-source    port 53;	
	query-source-v6 port 53;
	
	// Put files that named is allowed to write in the data/ directory:
	directory "/var/named"; // the default
	dump-file 		"data/cache_dump.db";
        statistics-file 	"data/named_stats.txt";
        memstatistics-file 	"data/named_mem_stats.txt";

};
logging 
{
/*      If you want to enable debugging, eg. using the 'rndc trace' command,
 *      named will try to write the 'named.run' file in the $directory (/var/named).
 *      By default, SELinux policy does not allow named to modify the /var/named directory,
 *      so put the default debug log file in data/ :
 */
        channel default_debug {
                file "data/named.run";
                severity dynamic;
        };	
};

view "internal"
{
/* This view will contain zones you want to serve only to "internal" clients
   that connect via your directly attached LAN interfaces - "localnets" .
 */
	match-clients		{ localnets; };
	match-destinations	{ localnets; };
	recursion yes;
	// all views must contain the root hints zone:
	include "/etc/named.root.hints";


	zone "the-playground.de" IN {
 		type master;
		file "the-playground.zone";
		allow-transfer { 192.168.1.92; };
	};

	zone "1.168.192.in-addr.arpa" IN {
		type master;
		file "the-playground.reverse";
	};
};

File: /var/named/the-playground.zone

$TTL 86400
$ORIGIN the-playground.de.
@ 1D IN SOA auxOEL5.the-playground.de. hostmaster.the-playground.de. (
 2002022401 ; serial
 3H ; refresh
 15 ; retry
 1w ; expire
 3h ; minimum
)
; main domain name servers
 IN NS auxOEL5.the-playground.de.
auxOEL5 IN A 192.168.1.82
; A record for mail server above
mail IN A 192.168.1.82
 
rac11gr2node1 IN A 192.168.1.90
rac11gr2node2 IN A 192.168.1.91
 
; sub-domain definitions
$ORIGIN rac.the-playground.de.
@ IN NS gns.rac.the-playground.de.
; sub-domain address records for name server only - glue record
gns IN A 192.168.1.92 ; 'glue' record

File: /var/named/the-playground.reverse

$TTL 86400 ; 24 hours could have been written as 24h or 1d
@ 1D IN SOA the-playground.de. hostmaster.the-playground.de. (
 2002022401 ; serial
 3H ; refresh
 15 ; retry
 1w ; expire
 3h ; minimum
 )
 IN NS auxOEL5.the-playground.de.
82 IN PTR auxOEL5.the-playground.de.
90 IN PTR rac11gr2node1.the-playground.de.
91 IN PTR rac11gr2node2.the-playground.de.

That’s it! Use service named restart to activate your changes.

Validating the configuration – testing the clients

So far so good. Let’s check that name resolution via DNS works on RAC node1 and node2. The debugging tools are dig and nslookup. My configuration uses the following settings on the client.

File: /etc/resolv.conf

nameserver        192.168.1.82
search            the-playground.de

options attempts: 2
options timeout: 1

File: /etc/nsswitch.conf

...
group: files

#hosts:  db files nisplus nis dns
hosts:   files dns

That should be enough for the moment, if your name service caching daemon is active it might be a good idea to stop it now. First we try forward resolution:

[oracle@rac11gr2node1 ~]$ nslookup rac11gr2node1.the-playground.de
Server:          192.168.1.82
Address          192.168.1.82#53

Name:    rac11gr2node1.the-playground.de
Address: 192.168.1.90

Now let’s try the reverse lookup:

[oracle@rac11gr2node1 ~]$ nslookup 192.168.1.90
Server:           192.168.1.82
Address:          192.168.1.82#53

90.1.168.192.in-addr.arpa  name = rac11gr2node1.the-playground.de.

[oracle@rac11gr2node1 ~]$

With the subdomain delegation, who answers my questions for domain “the-playground.de”?

[oracle@rac11gr2node1 ~]$ dig the-playground.de

; <<>> DiG 9.3.6-P1-RedHat-9.3.6-4.P1.el5 <<>> the-playground.de
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 29033
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0

;; QUESTION SECTION:
;the-playground.de. IN A

;; AUTHORITY SECTION:
the-playground.de. 10800 IN SOA auxOEL5.the-playground.de. hostmaster.the-playground.de. 2002022401 10800 15 604800 10800

;; Query time: 2 msec
;; SERVER: 192.168.1.82#53(192.168.1.82)
;; WHEN: Wed Oct 7 13:48:05 2009
;; MSG SIZE rcvd: 90

The important bit is the “AUTHORITY SECTION”. So, it’s working! I’ll write up my troubleshooting tips for DNS (I learned the hard way) in a future article.

We are ready to run runInstaller for the Grid Infrastructure now. Remember these points:

• Public hostnames go into DNS such as rac11gr2node1.example.com
• SCAN is NOT in DNS and will be created by DHCP. The SCAN address is in the subdomain, i.e. rac11gr2-scan.rac.the-playground.de
• The GNS VIP must be in the subdomain delegation section