The heartbeat installation steps must be repeated on both routers, the lvs-ldir01 and the lvs-ldir The ldirectored can be easily started and stopped by heartbeat. Your email address will not be published. Software Software used in this article: CentOS 6. See the schema below for more information. Make sure that firewall changes are saved and restored after a restart: service iptables save Ldirectord Setup Linux Director Daemon ldirectord is a background process computer program used to monitor and administer real servers in the Linux Virtual Server LVS cluster.
Now, for those of you out there who may have some experience with LVS, you can see exactly where this is headed — for everybody else, this might not be what you were expecting at all.
The first point is easy : there are two LBs for reasons of redundancy, as a single LB represents a single point of failure. In other words, if the LB stops working for whatever reason, all of your services behind it become functionally unavailable, thus, you really, really want to have another machine ready to go immediately following a failure. A little bit more explanation is required to explain the second and third points — but the short answer is two words : « Direct Routing » or DR for short.
From the LVS wiki :. It directly routes packets to backend server through rewriting MAC address of data frame with the MAC address of the selected backend server. It has the best scalability among all other methods because the overhead of rewriting MAC address is pretty low, but it requires that the load balancer and the backend servers real servers are in a physical network.
In a nutshell, requests get sent to the LB, which then passes it to the Web Server, who in turn responds directly to the client. All four are identical off-the-shelf servers running CentOS 5. The naming and numbering conventions are simple as well :.
You probably noticed the fifth item in this list, labelled « Virtual Web Server ». This represents our virtual , or clustered service, and is not a real machine. As the name implies, IPVS is implemented at the IP level which is more generically known as Layer-3 of the OSI model , and is used to spread incoming connections to one IP address towards other IP addresses according to one of many pre-defined methods.
It is powerful, but sort of a pain to use, which brings us to the second item in the list : piranha. Piranha is a web-based tool hence httpd, above for administering LVS, and is effectively a front-end for ipvsadm. You can define multiple logins if you like, but for now, one is certainly enough. Since the interface is served via an instance of Apache HTTPd , all we have to do is set up a normal «. Now, a full breakdown of. The username for the web login is « piranha », and the password is the one we set above.
The first screen — known as the « Control » page — is a summary of the current state of affairs. Moving on to the « Global Settings » tab, we have our first opportunity to start putting some settings into place :. You can apply and add as many real servers as you like, one at a time, in this fashion. Go ahead and set up B02 or whatever your equivalent is now. Luckily, this step is very, very easy. From the secondary :. That was a lot of work. Pulse, as a tool, is in the same family as some other tools you may have heard of, such as « Heartbeat », « Keepalived », or « OpenAIS ».
The basic idea of all of these tools is simple : to provide a « failover » facility between a group of two or more machines. Each of the load balancers runs an instance of « pulse » the executable, not the package , which behaves in this fashion :. The difference between the active and the inactive server is actually very simple : the active server is the one with the virtual addresses assigned to it remember those, from the Virtual Servers tab in Piranha?
Now is the time. The solution is simple, but the reason for the solution may not be immediately obvious — for that, we need to take a look at the IP layer of each packet neat!
Now imagine that Alice and Bob are hanging out with a few hundred million of their closest friends — but they still want to play ball. OK, so, those were some nice stories, but how do they apply to our Load Balancing setup? Notice anything? This does not work — it violates some basic rules about how communications are supposed to function on the Internet. Of course, the more balls Bob has to deal with, the more helpers he can use to spread the work around. The theory is sound, but how can we implement this in practice?
We simply add a dummy interface to each of the web servers that has the same address as the VIP, which will allow the web servers to interact with packets properly. This is best done by creating a simple sysconfig entry on each of the web servers for the required dummy interface, as follows :. Such an interface is assigned an address that can be accessed from management equipment over a network but is not assigned to any of the real interfaces on the device.
This loopback address is also used for management datagrams, such as alarms, originating from the equipment. The property that makes this virtual interface special is that applications that use it will send or receive traffic using the address assigned to the virtual interface as opposed to the address on the physical interface through which the traffic passes. Now, there is a known scenario in which a machine with a given loopback address will, in this particular situation, cause confusion on the network about which interface actually « owns » a given address.
And that, my friends, is that! If you have any questions, feel free to comment below remember to subscribe to the RSS feed for responses. Test states are injected into the kernel IPVS table using the ipvssync application. Configuration is highly extensible, so many testing protocols can be implemented easily. This package monitors hosts and informs the 2-node cluster when one of them dies. It includes Horms's code from "fake" below for IP address takeover. It is a general-purpose resource monitoring system.
We want to web servers were clustered with direct routing, we have to stop reverse ARP. I recommande to use arptables. Finally we create second loopback interface and we create alias of virtual ip address where web server will send queries. Same at both web servers. You are commenting using your WordPress. You are commenting using your Google account. You are commenting using your Twitter account.
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