16.7 Understanding a DNS-Based PSE Cluster Database

A DNS-based PSE cluster database is an ASCII text file that resides in the /etc/namedb directory. The name of the file usually has the format psecluster_domain_name.db .

Information in the PSE cluster database is entered in the form of case-insensitive DNS resource records, each starting in column 1 of the database file. All database resource records adhere to the format required for the DNS Internet (IN) class of data.

As shown in Figure 16-1, the database file information falls into seven main categories:

  1. Start Of Authority - Contains DNS- specific information
  2. Point of Origin Information - Sets the DNS domain origin of subsequent entries.
  3. Domain Definition Information - Sets up the Source of Authority (SOA) for this PSE cluster domain.
  4. Name Server Information - Sets up the DNS name servers (NS) for this PSE cluster domain.
  5. PSE cluster domain Origin - Starts the beginning of the PSE- cluster-specific domain information.
  6. Configuration Data Information - Defines known partitions, the default partition, the load update time, the communications service port, and shared file systems for the PSE cluster domain.
  7. Partition Definition Information - Defines partition members and communications.

In addition, the PSE cluster database can contain comments, which begin with a semicolon (;).

Figure 16-1 PSE Cluster Database File

The following sections describe each type of PSE cluster database information in more detail.

16.7.1 Point of Origin Information

Each .db file must begin with point of origin information, using the $ORIGIN control entry to set the DNS domain origin of subsequent entries. For example, the following entry sets the origin to abc.xyz.qwe.com : 

$ORIGIN abc.xyz.qwe.com.

In addition, you can use point of origin information to set up the configuration of partitions as subdomains of the PSE cluster domain. For example, the following entry sets the origin for the partitions and configuration_data in the domain mycluster to mycluster.abc.xyz.qwe.com : 

$ORIGIN mycluster.abc.xyz.qwe.com.

Note that domain names in database file statements must conclude with a period, indicating fully qualified DNS domains.

16.7.2 Domain Definition Information

Note
The serial number in the SOA must be incremented each time the file is edited. The PSE Database editor does this automatically for you.

A PSE cluster domain is expressed in DNS terminology as a SOA definition that identifies a unique domain name. All related information is defined in terms of subdomains of this PSE cluster domain. The following example shows a PSE cluster domain definition: 

mycluster       IN     SOA     abc.xyz.qwe.com. (
                postmaster@abc.xyz.qwe.com
                20
                300
                60
                1209600
                43200 )

The domain definition information is contained in a DNS SOA record defining a PSE cluster domain named mycluster . The enclosing parentheses that start at the end of line one and end on line seven allow the record to be continued beyond the first line.

Table 16-5 explains the contents of the fields in the SOA record.

Table 16-5 PSE cluster Database SOA Fields

Field  Description 
mycluster   Defines the name of the PSE cluster domain. 
IN   Indicates that the data in the domain definition is in DNS Internet format. 
SOA   Indicates that this is a SOA record. 
abc.xyz.qwe.com.   Specifies the host on which the database is created. 
postmaster@abc.xyz.qwe.com.   Specifies the address for the person in charge of the database data. 
20   The serial number that indicates the revision status of the data in the database file. 
300   The interval (in seconds) at which the secondary server tries to refresh its data. 
60   If the secondary server fails to connect to the primary server after the refresh period, it continues trying to connect at this interval (in seconds). 
1209600   The time (in seconds) at which the secondary server expires its data if it fails to connect to the primary server. 
43200   The time to live (TTL) (in seconds) that any server can cache the resource record. 

16.7.3 Name Server Information

The following example shows the entries for the primary and secondary DNS name servers for a PSE cluster domain: 

;
mycluster     IN      NS      server1.abc.xyz.qwe.com.
mycluster     IN      NS      server2.abc.xyz.qwe.com.
mycluster     IN      NS      server3.abc.xyz.qwe.com.
;

Table 16-6 explains the contents of the fields in the SOA record.

These fields are repeated for each name server in the PSE cluster domain.

Table 16-6 PSE cluster Database Name Server Fields

Field  Description 
mycluster   Indicates the PSE cluster domain that this name server serves. 
IN   Indicates that the data in the name server definition is in DNS Internet format. 
NS   Indicates that this is a name server record. 
*.abc.xyz.qwe.com.   Specifies the DNS domain name for this server. 

16.7.4 configuration_data Information

The configuration_data records define such PSE parameters as known partitions, the default partition, the load update time, the communications service port, and shared file systems for the PSE cluster domain. The configuration_ data records are entered through PSE DNS tokens in DNS text (TXT) format. The following example shows a database file configuration_data entry:

The configuration_data records define such PSE parameters as known partitions, the default partition, the load update time, the communications service port, and shared file systems for the PSE cluster domain. The configuration_ data records are entered through PSE DNS tokens in DNS text (TXT) format. Example 16-6 shows a database file configuration_data entry.

Example 16-6 configuration_data Database Entry

$ORIGIN mycluster.abc.xyz.com.
;
configuration_data IN   TXT     "PSE_PARTITIONS test compute servers"
                   IN   TXT     "PSE_PARTITIONS tools smp bigmem comp1"
                   IN   TXT     "PSE_PARTITIONS system comp2 allmembers"
                   IN   TXT     "PSE_SERVICEPORT 2233"
                   IN   TXT     "PSE_DEFAULT_PARTITION allmembers"
                   IN   TXT     "PSE_LOADSERVERS mach1 mach2"
;

The configuration_data resource record begins with the configuration_data subdomain designation in column 1, followed by a series of PSE DNS token entries in Internet TXT format. PSE DNS token entries must be enclosed in quotes. The configuration_data resource record is a required part of the PSE cluster database. Table 16-2 describes the PSE DNS tokens used for configuration_ data .

16.7.5 Partition Definition Information

The partition information begins with a subdomain designation containing the partition name in column one, followed by a series of PSE DNS token entries enclosed in quotes. The partition records are not a required part of the PSE cluster database. Characteristics can be defined at any partition level. If defined, new definitions have precedence over inherited values.

One of the characteristics of the PSE definition language is the ability to use groups to define other groups. This allows for easy definition, as well as attribute inheritance.

The example shown in Example 16-7 defines the set of PSE_MEMBERS for partition allmembers to be those of partitions system, compiler, test, gold, servers, tools, smp, and bigmem. Conversely, allmembers defines PSE_GROUPS for all of the listed partitions.

Example 16-7 Database Partition Definitions

;
test       IN   TXT  "PSE_MEMBERS mach3 mach4 mach5 mach6"
;
compute    IN   TXT  "PSE_MEMBERS mach1 smp1"
;
servers    IN   TXT  "PSE_MEMBERS server3 server1 server2"
;
tools      IN   TXT  "PSE_MEMBERS mach7 mach8 mach9 mach10"
;
smp        IN   TXT  "PSE_MEMBERS smp1"
;
bigmem     IN   TXT  "PSE_MEMBERS smp1"
;
system     IN   TXT  "PSE_MEMBERS mach11 tools"
;
allmembers IN   TXT  "PSE_MEMBERS system compiler test gold servers"
           IN   TXT  "PSE_MEMBERS tools smp bigmem"
           IN   TXT  "PSE_GROUPS users"