So I am looking at building a cluster server solution, and I found CARP. I am not sure if this meets my requirmeents, but I need an idential server, which can fail-over to if the one server goes down. CARP looks like it can do they, but I am not sure. How does it work, does it sync the full (everything) over? does it need like hardware? I am very new and just found it, and not sure what I need to review to understand it more.
Thank you
CARP is a fiendish hack that both awes with its brilliance and appalls with its utter crockishness. It works by sending
gratuitous arp messages to overwrite the record for a host that has failed in clients' ARP caches.
"Similar to other HA protocols, when a CARP node becomes a master it informs the neighboring routers and switches that it has a new MAC* address. It does this by issuing what’s called a
gratuitous ARP reply informing all of its “link up” event. This causes the neighbors to update their local arp tables and IP addresses that would originally be sent out the switch port associated with the old master will now exit the switch port for the new master (where the IP address has hopefully been assigned)."
Learn how to effectively maintain maximum availability during unexpected outages and perform seamless updates on production systems with absolutely no user downtime. All using a secure and well understood protocol.
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Machines in a CARP redundancy group will broadcast CARP messages at some set intervals. Backup machines will advertise less often than the master. They will become the master if they are advertising the most frequently i.e., the master has stopped advertising.
"When carp first runs, it starts as a backup and listens to the network to determine if it should become the primary. If at any time more than three times the node's advertising interval (defined as the advertising base (seconds) plus a fudge factor, the advertising skew) passes without hearing a peer's CARP advertisement, the node will transition itself to being a primary."
carp-rs allows a couple of hosts to share common virtual IP addresses in order to provide automatic failover. It is a portable userland implementation of the secure and patent-free Common Address R...
github.com
One of the limitations of CARP in modern cloud environments is that all the participating hosts must be in the same ARP broadcast domain. The virtualized networking that most cloud providers use doesn't emulate the ARP layer at all. I believe this is the case even for Vmware virtualization.
* The source says "IP address", but that's wrong. ARP maps MAC (hardware addresses) to IP addresses. The whole point of the exercise is to move an IP address from one machine to another. This means the IP address doesn't change, but the MAC address does.
