While I agree about the TTL and possibility of badly configured caching servers not honouring it, in the greater scheme of things it is really irrelevant.

This last change of address was urgently made by TMC, not realising it would impact us. It is only by blind luck that they hadn’t released the old address back to the amazon pool. If that had happened, every user would have had to manually sms their cars to make the change.

Luckily, they hadn’t released the address, so could assign it to another VM. I then did a socat on that machine, to forward the traffic to our new address. Then, some magic on the ovms_server.pl to reprogram cars connecting from the old address to switch to the new one. We’d done a similar thing a few years back, so I knew it would work.

Faced with that, a couple of hours of downtime, due to a DNS switch, is not so worrying ;-)

That said, I don’t see any option on register.com to set the TTL. Seems fixed at 4 hours. I’ll check further.

Regarding the change from server IP to server name, I would be grateful if more developers could try it, around the world. Let me know the results here. In particular, with the popular carriers in USA and Europe. It would be vastly simpler to just tell people to change to use a name, rather than messing around with google DNS servers.

Regards, Mark.

On 25 Sep, 2015, at 12:17 am, HONDA S-2000 <s2000@audiobanshee.com> wrote:


On Sep 24, 2015, at 5:46 AM, Collin Kidder <collink@kkmfg.com> wrote:
On Thu, Sep 24, 2015 at 5:38 AM, Michael Balzer <dexter@expeedo.de> wrote:
I just checked the DNS record for tmc.openvehicles.com:

tmc.openvehicles.com.    14399    IN    A    54.197.255.127

I suggest reducing the TTL to 1 hour before we recommend the change to
users.

Keep in mind that much of the internet is ruled by caching name
servers that will be quite stubborn about having to update their
records. I seriously doubt that a TTL of 1 hour will be honored by
much of anything. You're lucky if the ISP name servers bother to check
for updates more than once or twice a day.

I'm fairly certain that there are no caching servers that ignore TTL. It would thwart emergency services if short TTL values were ignored. My ISP has changed my server ip address only once, and they went through the same process of shortening the TTL before the scheduled change, then increasing it back to normal after the new ip address was activated.

The catch is that any change does not take effect until the old TTL expires. The "14399" above is 4 hours. So, if the TTL were changed to 1 hour, it would not take effect on all caching servers until 4 hours later. At that point, though, all DNS servers would be working with a TTL of 1 hour. The typical is more like 24 hours, so the 4 hour entry above is rather short. If 24 hours were used, then the ISP would need to start the process 24 hours early by changing the TTL to 1 hour a whole day in advance of the ip address change. But at long as you know the current TTL and plan ahead, it's always possible to make a prompt transition.

Those name servers that only bother to check once or twice a day are doing exactly as they're told, and will check every hour if told to do so instead.

Brian

_______________________________________________
OvmsDev mailing list
OvmsDev@lists.teslaclub.hk
http://lists.teslaclub.hk/mailman/listinfo/ovmsdev