Can DHCP be used with Serviceguard

[Ken Englander]

I have a limited understanding of DHCP and I have only been working with Serviceguard for a relatively short time. One of my associates has configured a system using DHCP. If I understand things correctly, it would not be possible to use DHCP with Serviceguard since it is necessary to specify IP addresses in the configuration file.

Am I correct?

(I tried to find an answer in the Serviceguard doc but found no reference to DHCP.)

Thanks!

Ken

[Rainer von Bongartz]

Ken,

absolutley no problem with DHCP running as a MC/SG package.

I have this running for years without any issue.

Configuration is simple, just put your configuration and leases folder on a shared LV, specify an IP Adress for the package and you are fine.

[Duncan Edmonstone]

Rainer,

I think Ken's question was about a Serviceguard node being a DHCPO client, rather than running a DHCP server...

Ken,

Assuming I'm right - then you are correct - Serviceguard *cannot* have its re-locatebale IP addreses (either node or package) serverd from a DHCP server.

Of course if the DHCP IP is going on an interface that serviceguard doesn't use in any way (i.e. doesn't appear in the nodes configuration within serviceguard) then it would work OK - just not failover to another NIC (for node and package IP addresses), or to another host (for package IP addresses).

The question I have is "why on earth would you want to do this anyway?"

HTH

Duncan

[Matti_Kurkela]

Rainer, putting a DHCP server into a ServiceGuard package certainly isn't a problem.

But I understood the original question as "can a ServiceGuard node be a DHCP client?". To that question the answer is definitely "no".

The main point of ServiceGuard is to make sure a given service (package) will always be available in a certain IP address, even if a node fails. So the package addresses will be allocated for use all the time. If the addresses are controlled by the DHCP server, the DHCP server becomes a Single Point of Failure that can make the entire cluster unreachable. To avoid that, you'll need a highly-available DHCP server.

There is another problem too: if the clustered services have dynamically-determined addresses, how are the clients going to find the clustered services to access them? If the answer is dynamic DNS updates, then the DNS master server will be a Single Point of Failure. To fix that, you'll need a multi-master DNS service... something like the DNS side of Active Directory on Windows, perhaps?

All this is effectively _increasing_ the total complexity of your cluster setup, which is generally not a good thing.

ServiceGuard is a Keep-It-Simple solution that relies on nothing more than the nodes themselves, the shared storage and the heartbeat connections. If these stay functioning, ServiceGuard will keep running even if the rest of the network goes dark.

MK

[Ken Englander]

Rainer - I was indeed asking if the system running SG can be a DHCP client, not a server, but thank you for your answer.

Our packages are a mix, but mostly do NOT offer an IP address for relocation. We use SG to provide shared VGs and raw LVs so we can relocate entire VGs in the event of failure and to run RAC.

So, Oracle handles the VIP for us. But I was thinking that SG requires the IPs for heartbeat to be specifically identified so it would not be possible for these to be dynamically assigned. That was really the main IP issue I was thinking about with my question.

Thank you all for your feedback!

Ken