Migration of leases from one failover pair to another without outage
Nick Urbanik
nicku at nicku.org
Wed Feb 27 06:03:35 UTC 2008
Dear Folks,
In migrating a lease from one pair to another, we have a situation
like this:
* we need to change the partners one at a time; here, from
secondary-a.test to secondary-b.test. However,
* the configuration on the primary needs to change to point to the
new secondary, and so it needs to restart to read this new
configuration.
Since a restart takes some 15 minutes or so, we would like to avoid a
situation where service is disabled for such a length of time.
Any suggestions on avoiding an outage?
Problem of moving from here:
Step 1:
+---------+ +---------+
| +-----+ | | +-----+ |
| |testa| | <-----------------------> | |testa| |
| +-----+ | | +-----+ |
+---------+ +---------+
primary-a.test secondary-a.test
+---------+
| |
| |
| |
+---------+
secondary-b.test
To here:
Step 2:
+---------+ +---------+
| +-----+ | | |
| |testa| | <---------\ | |
| +-----+ | \ | |
+---------+ \ +---------+
primary-a.test \ secondary-a.test
\
\ +---------+
\ | +-----+ |
\------> | |testa| |
| +-----+ |
+---------+
secondary-b.test
Stage 1:
In /etc/dhcpd.conf on primary-a.test:
failover peer "testa" {
primary;
address primary-a.test;
port 520;
peer address secondary-a.test;
peer port 520;
max-response-delay 60;
max-unacked-updates 10;
mclt 3600;
split 128;
load balance max seconds 3;
}
In /etc/dhcpd.conf on secondary-a.test:
failover peer "testa" {
primary;
address dhca1.test;
port 520;
peer address secondary-a.test;
peer port 520;
max-response-delay 60;
max-unacked-updates 10;
load balance max seconds 3;
}
Stage 2:
failover peer "testa" {
primary;
address dhca1.test;
port 520;
peer address secondary-b.test; # CHANGED => need restart.
peer port 520;
max-response-delay 60;
max-unacked-updates 10;
mclt 3600;
split 128;
load balance max seconds 3;
}
In /etc/dhcpd.conf on secondary-b.test:
failover peer "testa" {
primary;
address dhca1.test;
port 520;
peer address secondary-b.test;
peer port 520;
max-response-delay 60;
max-unacked-updates 10;
load balance max seconds 3;
}
Or indeed, I'd love to hear any other suggestions for migrating leases
from one failover pair to another without an outage.
--
Nick Urbanik RHCE http://nicku.org nicku at nicku.org
GPG: 7FFA CDC7 5A77 0558 DC7A 790A 16DF EC5B BB9D 2C24 ID: BB9D2C24
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