10-07-2019
It is
usually (but not always) better to keep to a single A record for an IP address with a matching PTR record so the IP address can be used to find out the host. Other things, such as service names or alternate domain entries can be added as CNAME or alias records. If you have a service that other things connect to and use that has a logical name, then it is
usual to define that as an alias. When you come to replace your servers, if the applications all use a CNAME/alias then you can edit the DNS to move the alias to point to the new server when you are happy that it is ready.
Additionally, if you have a cluster of servers, you might consider more things. For an Active/Passive cluster, you would have an A record for each server, but make every connection to the application(s) to use a separate IP address that you move to the active server, a virtual IP if you like. Consider:-
- ServerA: 10.10.10.1 with PTR of 10.10.10.1 to ServerA
- ServerB: 10.10.10.2 with PTR of 10.10.10.2 to ServerB
- ServerC: 10.10.10.3 with PTR of 10.10.10.3 to ServerC
- Myapp: 10.10.10.101 with no PTR record
Make the 'active' server also offer the
Myapp IP address and make connections point to service name
Myapp
For an Active/Active cluster, you need some sort of load-balancer, but that's a whole extra topic.
What do you actually want to do with the applications offered by the server and how would you consider transferring them to a replacement later?
Robin
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LEARN ABOUT DEBIAN
net::nslookup
Net::Nslookup(3pm) User Contributed Perl Documentation Net::Nslookup(3pm)
NAME
Net::Nslookup - Provide nslookup(1)-like capabilities
SYNOPSIS
use Net::Nslookup;
my @addrs = nslookup $host;
my @mx = nslookup(type => "MX", domain => "perl.org");
DESCRIPTION
"Net::Nslookup" provides the capabilities of the standard UNIX command line tool nslookup(1). "Net::DNS" is a wonderful and full featured
module, but quite often, all you need is `nslookup $host`. This module provides that functionality.
"Net::Nslookup" exports a single function, called "nslookup". "nslookup" can be used to retrieve A, PTR, CNAME, MX, NS, SOA, and TXT
records.
my $a = nslookup(host => "use.perl.org", type => "A");
my @mx = nslookup(domain => "perl.org", type => "MX");
my @ns = nslookup(domain => "perl.org", type => "NS");
my $name = nslookup(host => "206.33.105.41", type => "PTR");
"nslookup" takes a hash of options, one of which should be term, and performs a DNS lookup on that term. The type of lookup is determined
by the type argument. If server is specified (it should be an IP address, or a reference to an array of IP addresses), that server(s) will
be used for lookups.
If only a single argument is passed in, the type defaults to A, that is, a normal A record lookup.
If "nslookup" is called in a list context, and there is more than one address, an array is returned. If "nslookup" is called in a scalar
context, and there is more than one address, "nslookup" returns the first address. If there is only one address returned, then, naturally,
it will be the only one returned, regardless of the calling context.
domain and host are synonyms for term, and can be used to make client code more readable. For example, use domain when getting NS records,
and use host for A records; both do the same thing.
server should be a single IP address or a reference to an array of IP addresses:
my @a = nslookup(host => 'example.com', server => '4.2.2.1');
my @a = nslookup(host => 'example.com', server => [ '4.2.2.1', '128.103.1.1' ])
By default, when doing CNAME, MX, and NS lookups, "nslookup" returns names, not addresses. This is a change from versions prior to 2.0,
which always tried to resolve names to addresses. Pass the recurse => 1 flag to "nslookup" to have it follow CNAME, MX, and NS lookups.
Note that this usage of "recurse" is not consistent with the official DNS meaning of recurse.
# returns soemthing like ("mail.example.com")
my @mx = nslookup(domain => 'example.com', type => 'MX');
# returns soemthing like ("127.0.0.1")
my @mx = nslookup(domain => 'example.com', type => 'MX', recurse => 1);
SOA lookups return the SOA record in the same format as the `host` tool:
print nslookup(domain => 'example.com', type => 'SOA');
dns1.icann.org. hostmaster.icann.org. 2011061433 7200 3600 1209600 3600
TIMEOUTS
Lookups timeout after 15 seconds by default, but this can be configured by passing timeout => X to "nslookup".
DEBUGGING
Pass debug => 1 to "nslookup" to emit debugging messages to STDERR.
AUTHOR
darren chamberlain <darren@cpan.org>
perl v5.12.4 2011-08-15 Net::Nslookup(3pm)