tinydyndns - failover
Prepare failover for tinydyndns DNS service
Prepare failover for tinydyndns POP service
How to switch services to the failover machine
What can make the tinydyndns service fail?
- The nameserver handling the delegation to the tinydyndns
domain is unavailable
- The nameserver running the tinydyndns service is unavailable
- The POP server handling the POP service for tinydyndns is
unavailable (normally the same server as in 2.)
How can I provide failover services in these cases?
- Make sure you have multiple nameservers providing the delegation
to the tinydyndns domain.
Refer to the djbdns documentation
on how to
replicate your DNS service.
To provide failover for your tinydyndns services, you need to
have control over the servers handling the delegation.
- tinydyndns doesn't support automatic replication of its
dynamic DNS data, so the tinydyndns domain cannot be handled by
multiple servers simultaneously.
But you can prepare one or more additional machines to handle the
tinydyndns services in case the primary machine is unavailable,
- To be able to switch over the POP service to another machine in case
the primary machine is unavailable, you need to replicate the POP password
database for the dynamic hosts whenever it changes, so that the failover
machine knows about all dynamic host names that are handled by this
See below on how to do this.
How to prepare a failover service for dynamic DNS data
Simply configure tinydyndns on the machine
that should take over the tinydyndns and POP service in case the
primary server is unavailable.
Of course configure tinydyndns to handle the same domain name as
the primary tinydyndns server, on an IP address of this failover
Adjust the TTL (time to live) of the delegation to the tinydyndns
domain to your need (say four hours).
This is the worst case downtime of the tinydyndns service in case
the primary tinydyndns server gets unavailable, and after the
administrator takes action.
Switching over the services currently needs manual intervention.
How to automatically replicate the POP password database
The tinydyndns password database is changed by the
./setpasswd script only.
To have the database replicated automatically when setpasswd is
run, add a line that copies or syncs the passwd file to the
failover machine to the end of the setpasswd script (remove the
last line ``exit 0'' first).
E.g.: A primary tinydyndns service runs on
The failover service is prepared on a server with the IP address
Add this line to /service/tinydyndns-pop/setpasswd on
# cd /service/tinydyn-pop/
# cat >>setpasswd <<EOT
rsync -e ssh passwd a.b.c.d:/service/tinydyn-pop/passwd
How do I switch services to the failover machine
First rebuild the data.cdb from the current passwd database on
the failover machine:
# cd /service/tinydyn/root
# make rebuild
Now change the delegation on all available DNS servers that handle the
delegation to your tinydyndns domain to delegate the domain to
the IP address of the failover machine is running tinydyndns on.
Within the next four hours (or whatever you've set as TTL), clients that
try to update there dynamic DNS entry, and clients that ask for dynamic IP
addresses of hosts in your tinydyndns domain, will switch to
contact your failover machine.
Gerrit Pape <email@example.com>