Linux Failover?

Anton asks: "This is a question about Linux failover in business situations. We are a growing B2B company; our product runs on Apache/Linux. We contracted professional services to properly set up our network. After all the hellishly expensive CISCO hardware had been set up it turns out that for our servers to be configured for failover, each one needs two dual-port NICs configured for one IP connected to two different switches, furthermore the driver needs to intelligently switch the ports when the active port fails ... We've never heard of such beasts for Linux and a net search revealed nothing. Our consultant however claims that 'Linux is biting itself in the foot' for not supporting that, and that other industrial strength OS's like solaris in fact do support this. Has anyone run into this before or have other ideas? " [nik suggests]: Take a look at Polyserve Understudy, which might be an alternative. FreeBSD and Linux versions are available (and bundled with FreeBSD 4.0).

Comments

Easy solutions

[sdw]

First, it wouldn't be that difficult to modify the kernel to support this. I've released patches to work around bugs in the ARP reply with two NIC's. Routing to the active port shouldn't be too difficult.

A non-kernel invasive version of this would be a script that configures one port with the desired IP/mask and creates the default route. It then puts the other port in promiscuous mode and monitors it for traffic using a libpcap based program or even a possibly modified tcpdump. As soon as it sees any traffic, it switches the configuration and starts monitoring the other port. This could probably be written in 2-4 hours given a network to test it in.

For a possibly simpler solution (i.e. no code to write), use a pair of additional Linux systems. Configure each of them to load balance with LinuxVirtualServer (aka LinuxDirector) or the Pirhana version of it to as many backend servers as you have, BUT to Different internal IP addresses. Good choices would be 10.* addresses, say 10.0.1.* and 10.0.2.*. Using either a dual NIC or two NIC cards in each server, create two networks with one for each of the load distribution servers. Configure Apache et al to respond to the IP addresses of each network the same.

BTW, there are 4 port 100-base-T cards out there, from Adaptec I think.

Good Luck!

Linux High Availability project

[dashuhn]

You may want to check out http://linux-ha.org/.
The "heartbeat" application implements node-to-node monitoring over a serial line and UDP and can initiate IP address takeover based on a notion of resources provided by nodes and resource groups. It worked well for me. However, this was only a very basic two-node setup.

Shoot your consulatnt

[arivanov]

Shoot your consultant. With a big gun. Only an idiot will suggest a layer 2 failover for a unix system.

1. Your consultant should learn routing protocols

2. Your consultant should learn the concept of a loopback alias.

3. Your consulatnt should have an IQ of above 25

4. There is absolutely no need for link layer 2 failover where layer 3 will do. Unix is not WinHoze. It knows about routing.

So your task list is:

• Configure loopback aliases on the linux boxes.
• Configure apache to listen only the loopback alias interface.
• Build gated from rhat sources they have the patches for linux-2.2 in already. You may use zebra CVS instead but it is still a bit off in terms of stability. You may need a script that HUPs it a few times gated as gated does not always start clean and update the routing table on 2.2.x.
• Configure ospf on gated and on your cisco gear. Distribute default into OSPF as gated from the 3.5.x tree has no IRDP.
• Shoot your consultant

In btw: your bill is 500$.

Linux does support this...

[austad]

You could go with an expensive commercial solution like BigIP from F5, but those will run you at least $30k or so. You could also use Polyserve Understudy, which does pretty much the same thing only under Linux, and it's only about $400 or so. If you have all this expensive Cisco equipment and a Cat6000, you can run Local Director on that without buying additional hardware.

However, I suggest:
http://www.linuxvirtualserver.org or
http://linux-ha.org or
http://www.eddieware.org

It all depends on your application that you're running. If it's just http, any of these will work, but if it's something else, you're stuck with linux-HA or Linux Virtual Server. Eddie will only do http as far as I know. Plus Eddie uses Erlang, which may affect performance.

Wrong failure being addressed

[igaborf]

You're attacking the wrong problem. What you need first is not Linux failover but consultant failover: Your consultant has failed; you need to switch to a new one instantly.