[Consortium] Linuxaudio.org server migration

[Bent Bisballe Nyeng]

On 01/27/16 05:12, Ivica Ico Bukvic wrote:
> I am pleased to report we are at the very end of what has proven to be a
> fairly intense journey (needless to mention I learned a lot more than I
> ever wanted to about sysadmin).
...
> As we enter the final stage in the porting
> process, there will be a brief downtime tentatively scheduled for 11am
> Eastern Time (East US Coast) tomorrow, Wednesday, January 27th.
Hi Ico

I thought I would share a hint on server migration wrt dns configurations.
The dns configuration has a ttl field. This field signifies to the 
clients how long the ip address they get when they do the lookup is 
valid, ie. the time that must at-most pass before they ask the dns 
server again.

When changing the ip address in a dns configuration all the clients who 
already have a valid token will keep on using this token (with the old 
ip address) until their respective ttl's have expired.

This is what I usually do to solve this problem:
Lets assume the current ttl is set to 86400 (24h).
24 hours before I plan to do the migration I set the ttl to 3600 (1h).
Then 1 hour before the migration I change it again, this time to 600 (10m).
And finally 10 minutes before the migration I change it to 0.
At the time of migration I now know that all clients are asking the dns 
server for ip all the time and nobody will get the wrong (old) ip 
address once I have changed it.

When the new ip address has been set in the configuration the ttl can 
now be changed back to 86400.

The amount of "steps" to use (24h, 1h, 1m, ...) highly depends on the 
amount of dns lookups on the dns server since setting the ttl to 0 24h 
before migration might result in a serious extra dns server load.

Good luck with the final migration :-)

Kind regards
Bent Bisballe Nyeng