RE: [cobalt-users] Redundancy with two RaQs

[<rpaiz@xxxxxxxxxxxxxx>]

Johnny,

> As my web hosting business is growing, I am loosing sleep 
> thinking in a preventive setting to prevent downtime for
> the case of a crash in my RAQ hard disk.

Thank God you're losing sleep *before* it happens. Doing so
afterwards can get very expensive... :)

> I understand that the RAQ domain and IP address is used as 
> the first DNS server for virtual sites. So I point all
> domains in the server to this DNS,and it works fine.
> 
> The problem is that I have the second DNS in the same RAQ,
> so if this device crashes, I will have to face inmediate
> downtime for all the domains contained in this server.

Not good. Actually, worse than you think.

When your webserver is down, the browser gets an error saying
"Page Temporarily Unavailable," and the customer gets upset
because they can't get to the site. But when all your DNS is
down, the browser gets an error saying "Site Does Not Exist"
and your problems become very, *very* large.

You must have your primary and secondary DNS servers in
different machines (and ideally on different networks) in
order to do things right. This way, if your DNS-1 machine
goes down, your DNS-2 answers. And if you have them on
different networks, even the Internet link to Network-1 can
go down and DNS-2 still answers.

> I am planning to co-locate a second RAQ with a different 
> provider, in order to have redundancy.

Where is your first colocated? USA, or CR? I might be able
to colocate your RAQ if you're interested. I can't compete
with the pricing on USA-based networks, but we'll see...

> I will have four IPs in each RAQ

Let's talk about this. Why four? Do you need them? Are your
sites using secure servers (SSL), anonymous FTP, or something
else that requires their having indiviual addresses? If not,
I suggest you're better off using name-based addresses...

> Can somebody be so kind to explain how should I set the DNS 
> servers for a given domain so that the first DNS is in the
> first RAQ and the second DNS in the second RAQ?

Let me go through this in a simple way. No credit for the work,
I learned this on the list too...

First off, MASTER and SLAVE servers are completely different
from PRIMARY and SECONDARY servers as far as DNS is concerned.

The MASTER server is where you input all the records you want,
like mail.domain.com or support.domain.com. The SLAVE server,
or servers if you have more, get their information directly
from the MASTER without you doing anything.

On the other hand, the PRIMARY nameserver is the one which
everyone asks first. The SECONDARY server only gets asked if
the primary is down.

Now, the primary is usually the same as the master, but it
doesn't have to be. For example, say you're really small and
your ISP is really big. You set your DNS to be the master and
the ISP's DNS to be the slave; that way you can change any
records you want anytime without asking them. BUT you set the
ISP DNS to be the primary, and that way everyone asks them
first. Since they have a better server and a better network,
they answer quickly and even if yours goes down.

Getting back to your specific question:

* Set the DNS in your RAQ to be the MASTER and PRIMARY.
* Somewhere else in the world, get another DNS to be SLAVE
  and act as SECONDARY. This could be, for example, a DNS
  server at RACSA or at the place where you registered your
  domain.

> Where do I put the virtual site content for this domain? 
> RAQ1? RAQ2? or BOTH RAQs? What happens with email? How does
> the RAQ2 gets content in the case of a crash of RAQ1?

You put the site content wherever you want.

Now you've fixed DNS properly and your sites are hosted, for
example, on RAQ#1. Then, as to how you get redundancy, that's
another question entirely.

For mail, you can have two MX records for each domain. One
has high priority and the other low priority. Your primary
mail server is the high priority, and some other server is
the low priority. The second server can hold your mail in a
queue if the first goes down. The customers won't be able
to get their mail if RAQ#1 goes down, but the mail won't
bounce. Then, when RAQ#1 recovers, it'll get all the mail
it missed while it was out.

I'm not sure what the best way to get HTTP redundancy is
right off the bat... let me look into it.

Also, it occurs to me that we could do secondary DNS for
each other. That way, I set my DNS server to respond as a
secondary nameserver for your domains, and you set yours
to respond as secondary to mine. Simple, fast, and we
get perfect redundancy for both of us.

-- 
Rodolfo J. Paiz
rpaiz@xxxxxxxxxxxxxx <mailto:rpaiz@xxxxxxxxxxxxxx>