Two Power-1 vs. One Power-2 [Archive] - Defender Hosting Forums

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Bogdan

08-20-2005, 04:39 PM

Hi,

I would like to hear you opinions about that.
Which is best? Having 2 Power 1 VPSs or just one Power 2?
Which are the advantages and disadvantages?

Bogdan

elix

08-20-2005, 04:59 PM

If you have some clients that are using tons of resources and some that are using very little you can balance them amongst both VPSes. Also if one VPS is down, the other will still be up so not all of your clients will have a down'd site. You can use the second as a backup MX record for your own site, then you won't lose mail, etc.

But, if you're hosting just one site that's intensive, the single Power-2 is best.

Zaf

08-20-2005, 05:10 PM

..... and if you choose two Power-1 instead of a single Power-2, have the other one hosted in a different DC (if feasible and convenient) (PVPS provides that i guess), if not atleast have the second one on a different node.

elix

08-20-2005, 05:40 PM

Robert

08-20-2005, 09:53 PM

But you can have the site on a different hardware node. :)

charles

08-23-2005, 05:25 PM

Bogdan, if you use cpanel, I would recommend two power-1 instead of one power-2 as you can take advantage of dns clustering, and load balance your customers easily if needed. If you did have a problem with one vps, then only half your customers are affected, etc.

The downside of 2 servers is increased maintenance/management time, but it shouldn't be much more work for you given cpanel and us.

BTW, there should be a thread covering this already somewhere on the forums.

charles

Bogdan

08-23-2005, 05:32 PM

Actually I am also considering two VPSes instead of one but I just wanted to check your opinions.
Can you please explain the concepts of dns clustering and load balancing?

Thank you,
Bogdan

charles

08-23-2005, 05:42 PM

Cpanel has built in DNS clustering thats pretty well documented on their site. It's easy to configure (and we can do this for you) and once setup, anytime you add an account to any server in the cluster, the dns gets updated on the others. So you can have truly redundant DNS (not just 2 different IPs on the same server).

Load balancing is just a manual thing. If you get a heavy resource customer you can shuffle accounts around to get the best use out of both.

hth
charles

Zaf

08-23-2005, 05:54 PM

would it be possible to have NLB/failover cluster for some accounts/domains for their website. How would mysql data be handled for such domains?

elix

08-23-2005, 08:15 PM

would it be possible to have NLB/failover cluster for some accounts/domains for their website. How would mysql data be handled for such domains?
I'm not sure but I believe you can use rsync for the MySQL data.

charles

08-24-2005, 12:09 AM

Anything is possible, but no it wouldn't be easy. Without it being built into your application, clusters are not aware of your application/data so you can't have writes to the database etc.

As far as synching mysql with rsync, I would be wary of that for true data integrity unless you shut it down for a final rsync. I would use mysql replication instead - thats whats its for. But see above :)

charles

Starchild

08-24-2005, 01:26 AM

How about mail redundancy? I mean a failover system when one server goes down the other take s its place serving emails like nothing has happened. Would that be possible?

jpetrov

08-24-2005, 06:34 AM

Very practical question:

is VLAN possible between two VPS-es (I know you will point me to the OpenVPN FAQ in knowledgebase) but - is inter-VPS VLAN traffic metered?

elix

08-24-2005, 08:47 AM

Very practical question:

is VLAN possible between two VPS-es (I know you will point me to the OpenVPN FAQ in knowledgebase) but - is inter-VPS VLAN traffic metered?
VLAN is not possible. I believe it is metered.

charles

08-24-2005, 09:07 AM

How about mail redundancy? I mean a failover system when one server goes down the other take s its place serving emails like nothing has happened. Would that be possible?

Again anything is possible, but no, this isn't going to be done for you or easy to do either.

I personally don't think mail redundancy is needed. First off, mail isn't just dropped - a properly configured mail server will try to resend for days. Then if it finally gives up, the sender is notified anyway.

charles

Starchild

08-24-2005, 09:44 AM

Again anything is possible, but no, this isn't going to be done for you or easy to do either.

I personally don't think mail redundancy is needed. First off, mail isn't just dropped - a properly configured mail server will try to resend for days. Then if it finally gives up, the sender is notified anyway.

charles
I understand that receiving mails would not be lost for as you say the sender will keep trying for days. But that's not what I would be interested in.

Instead what I'm saying is a situation where the client is always able to connect to his mail server and perform send and receive no matter what.

Example scenario:

- srv1 has mail services up and running.
- srv2 acts as backup and is synced with srv1 (mail accounts only)
- srv1 sends heartbeat signals to srv2 to say I'm alive and kicking (srv2 does likewise)
- srv1 goes down
- srv2 fails to receive heartbeat signals from srv1 and takes its place (and sends a failiure notice to the admin)
- the client sees no difference as he's being served from srv2 which is a mirror image of srv1 (again email only)
- srv1 comes back up and starts sending heartbeat signals to srv2
- srv1 gets synced with srv2 and becomes the backup for srv2
- the cycle continues
- the customer is happy

Am I unnecessarily complicating things?

charles

08-24-2005, 09:52 AM

I understand exactly what you want, and thats what the "Again anything is possible, but no, this isn't going to be done for you or easy to do either. " part of my response was addressing :)

There are too many reasons to list why this is very difficult to do (these are typical HA issues - google for this and you'll see), but there is nothing stopping you trying to implement this yourself :)

charles

Starchild

08-24-2005, 10:05 AM

elix

08-24-2005, 11:05 AM

Zaf

08-24-2005, 11:05 AM

I personally don't think mail redundancy is needed. First off, mail isn't just dropped - a properly configured mail server will try to resend for days. Then if it finally gives up, the sender is notified anyway.Well, there are a couple of things to consider in this case...firstly my mail server is just at the receiving end of the mail, I cannot control the other mail server's retry policy i.e. time gap between each retry and the number of retries even. All the mails which knock at my server during a failure of my server, would be delayed (who knows how long)...which reminds me ...... "Mail delayed is as good as Mail denied" :D ;)

charles

08-24-2005, 11:12 AM

Yes, I was just interested in seeing if this was possible and how hard would it be. Writing it on paper it seems reasonably easy but I guess when it comes to actual implementation things get to be different. Any good papers on this around? I have already googled but most of what comes up is too complicated and overkill for a simpe 2 server solution aiming for email redundancy. Most are about full blown load-balancing stuff requiring numerous servers.

It *is* complicated, and it *is* difficult, which is why all you see are complex solutions. The problem with HA for mail is that the data changes very frequently, and in seconds you can get horribly out of sync. Typically people use a single backend server to store the content, and multiple front ends to handle the service(s) but you still have a single point of failure and they are geared more towards high performance and scalability than HA.

If you are really interested in this topic, visit http://www.linux-ha.org/ and signup on their mailing list and ask away.

charles

Starchild

08-24-2005, 01:03 PM

Thanks Charles, great site.

mikelbeck

08-24-2005, 01:07 PM

You may be able to pick up a Power-0 and use it for backup MX and DNS and just get one Power-2 at the same time. You can setup the Backup MX to store the e-mails and "re-deliver" them once the main server is up. I'm not an expert at this but I know it's possible to do that.

I use dnsmadeeasy for this. Secondary DNSs and secondary mail servers are hosted there. Cheaper and easier than configuring a new VPS for just that.

Fred

08-24-2005, 01:42 PM

Well, secondary dns and backup mx service are not clusters of course... but they do the job for mail and dns... And mikelbeck said, it's easier and cheaper.

A good primary and secondary dns service is, for me, https://www.xname.org/
They are free of course! Source is also available http://source.xname.org/ ( i never looked at it ... )

They saved my life when my two dns server on my "another-provider-vps" wasn't reachable by any sympatico customers ( Sympatico is a big canadian ISP ).
They were able to contact the site by using the ip of my "another-provider-vps", but wasn't able to contact the site by using the domain name. Sympatico is a big isp in canada, so i looked for a backup dns service to add a third dns server to the domains i host...
Some of my customers noticed a lost of 45% of their unique hits before i added the third dns server!!

The only problem i have with xname.org is they use a .org domain.
So if you have a .com domain with a dns in the .org, net, info, etc., the initial dns lookups will be a bit slowest than with a .com domain with a dns in the .com.

I believe the "solution" is to point ns3.domain.com to the xname.org ip... i didn't tried :)

Important thing to note is that i prefer to have a backup dns and backup mx service outside my vps provider datacenter...

Zaf

08-24-2005, 02:49 PM

I believe the "solution" is to point ns3.domain.com to the xname.org ip... i didn't tried :)Most of these Free DNS providers or even paid DNS providers wont allow you custom name server names. Some of them even terminate your account if you do that. Even xname does not allow that i believe, not sure if they enforce it though. DNSMadeEasy.com is indeed one of the best DNS service providers. dnsstuff.com and dnsreport.com use the same service too...

Some free DNS provider sites I know of are:
http://www.zoneedit.com
http://www.granitecanyon.com
http://www.everydns.net

vps-vince

08-24-2005, 04:14 PM

Here is a link to an article which contains a PDF on the basic setup of Heatbeat systems:

Learn to build a high availability server pair using the Linux Heartbeat package:

http://techrepublic.com.com/5138-1035-5838608.html?tag=nl.e101

This sample chapter from The Linux Enterprise Cluster (No Starch Press) explains how the Heartbeat package enables you to build an inexpensive system that will fail over a resource from one server to another. Topics include physical connections between servers, Heartbeat control messages, failing over resources, and resource scripts.

Brief registration required.

- Vince

DMHosts

08-25-2005, 10:54 AM

So does this mean you can have NS1 & NS2 used on two or more servers? Removes the need to have NS3, NS4...?

Cpanel has built in DNS clustering thats pretty well documented on their site. It's easy to configure (and we can do this for you) and once setup, anytime you add an account to any server in the cluster, the dns gets updated on the others. So you can have truly redundant DNS (not just 2 different IPs on the same server).

Load balancing is just a manual thing. If you get a heavy resource customer you can shuffle accounts around to get the best use out of both.

hth
charles

charles

08-25-2005, 11:14 AM

Yes you can have ns1 on one vps and ns2 on another, and as long as they both serve the same DNS info (as in the case of cpanel's DNS clustering) this is as ideal as it gets in my opinion. ns3 and ns4 could provide even more redundancy if you had additional servers, but without additional servers they are pointless.

charles