Connect and share knowledge within a single location that is structured and easy to search. If I am correct the configuration will be propagated to node2. The resource group is going to monitor one of the service in the machine. My question is, because the 2 nodes are running identical service, which one is becoming the active node firstly?
Or the linux heartbeat will decide that the two has equal possibility? With Pacemaker you don't have 'an active node' and 'a passive node'. All cluster nodes there may be more than 2 can run services equally and the rules in the CIB database tell CRM Pacemaker's resources manager what node can run what services.
If you configured the service to run as a single instance that can run on both nodes with no constraints, then you cannot tell which node will run it. If you have two such services then you may end with one running on one node and the other on the other node. For the first service node1 will be active and for the second — node2.
You define actual preference by declaring some constants. Example: 'run service 1 on a node where service 2' is running or 'always prefer node 1 for both services'. Usually you have a service which defines 'a logical master' — it can be an IP address or DRBD volume in the primary state — then all other services depend on this and you choose the 'master' by setting preferences for the primary service.
Sign up to join this community. The best answers are voted up and rise to the top. Towards this end, it is necessary that old versions of the software should be able to accept messages from new versions of the software, and ignore fields in the messages which they do not understand. This is an undertaking of moderate difficulty, requiring careful thought on the design of new messages to be sent in the cluster and how they will be interpreted by the old software.
In this design, a communications system like heartbeat can be of some help. Some message formats are designed to easily allow software to ignore fields they don't understand, and yet still find the information they need in the fields they do understand.
Towards this end, messages in the heartbeat system are designed in a fashion similar to the environment strings which UNIX TM 2 supplies to processes. New message formats most commonly add new name, value pairs. In some cases, it is desirable to effectively change the semantics of a given name.
When this situation occurs, there are various techniques available to handle it. One of the most common ones is to have the new version of the software continue to supply the old name semantics through the old name, and redundantly supply a new name, and the new semantics associated with it through the new name, value pair.
Although there are various techniques to deal with this situation, this message format has the advantage of being very simple, easy to understand, and yet very flexible. As a bonus, it is a simple matter to provide the contents of a message to a shell script. The message format heartbeat adopted is simple, and easy to understand, but has a few disadvantages. ASCII data is bulky, and having names in every message makes it more so. This extra bulk is primarily of concern for heartbeat messages, which constitute the majority of data in the cluster communication.
This has been made a little less problematic by choosing short field names for the fields found in heartbeat messages. This trades message bulk off against a little obscurity for heartbeat messages. With strong authentication, current heartbeat messages are approximately bytes in size.
It is believed that this size of message is small enough to justify the design chosen. The initial implementation of heartbeat had a very simple prototype API for communication with management layers of the cluster.
In this API, each cluster message caused the invocation of a process to which the message was given. Simple rules were used for filtering out heartbeat messages in which no state changed i. This interface is extremely effective and easy to put together scripts to manage a 2-node cluster. This prototype communication mechanism proved adequate for some simple purposes, and allowed easy assembly of a very basic some might say crude cluster manager for two nodes.
However, a more sophisticated cluster management functions need more state information, and need to be continuously running in order to negotiate with other nodes. This is a critical need for clusters with greater than two nodes. The prototype API fell short in many respects. These include:. Ability to adequately isolate the client process from the implementation details. Since the prototype API was designed as a vehicle for demonstrating heartbeat , none of these limitations came as any surprise.
At the time of this writing, this new heartbeat API has been implemented and is now in the testing phase. This API provides the following basic services:. It is expected that this API will allow heartbeat to become useful in a wide variety of circumstances, ranging from normal HA operations, through integrating with other cluster managers, through integrating with cluster file systems.
This technique allows cluster systems to safely use shared disk arrangements. An API has been defined for this technique, and an implementation was created. Although it is useful now, it will be more useful in the future, with a new cluster management infrastructure. At this point, the API and implementation will appear in heartbeat and several other open source cluster managers.
There are many possibilities on the horizon for heartbeat. These possibilities have been considerably broadened by the recently introduced API. These include. Currently, heartbeat does all of its UDP communication using broadcast packets.
This limits the cluster to being all on one subnet, and causes unnecessary interrupts on machines which are on the subnet but not part of the cluster. It would be good to implement multicast communications in order to alleviate these concerns. At the present time, it is necessary for all the members of the cluster to have their authentication data updated manually.
It would be desirable to have a way to distribute keys across the cluster, perhaps using openssh or some similar mechanism. Although LinuxFailSafe currently has heartbeat and membership mechanisms of its own, there are enough things that heartbeat does better, that it is expected to prove desirable to replace portions of FailSafe with heartbeat. There are at least two efforts underway to add a GUI configuration and status front end to heartbeat.
Conectiva has written a linuxconf module for heartbeat , and David Martinez has prototyped a GUI configuration tool for it [ Mar00 ]. Heartbeat provides only a local view of cluster membership. That is, it only knows about or is aware of each node's own individual view of the cluster membership. This is adequate for some purposes, but inadequate for many.
If the local medium has no communication asymmetries, and the same configuration, then there is no difference between the local and the global view. However, if communication is impeded due to hub or switch bugs or routed multicasts, then it is possible for different members of the cluster to have differing views of what the membership of the cluster actually is.
It is important that every member of the cluster have the same view of cluster membership as every other member. It is necessary to have a consensus membership layer which then shares cluster membership information across the cluster, so that each machine has the same view of the cluster membership. Certain kinds of clusters use the model of barriers in their implementation. The TweedieCluster is an example of such a cluster [Twe00]. According to Tweedie, a barrier provides a guaranteed synchronization point in distributed processing which is valid over all nodes in the cluster: it strictly divides time into a pre-barrier and a post-barrier phase.
The barrier may not necessarily complete at exactly the same time on every node, but there is absolute guarantee that the barrier will not complete on any node unless all other nodes have begun the barrier. IBM's Phoenix Cluster technology has the concept of providing a tool kit to implement generalized n-phase transactions to achieve synchronization across the cluster [Pfi98].
These are similar in function to the barrier API described above, but are more general. In this model, a transaction is begun in which a machine names a next state. Each node participating in the transaction then sends a message nominating the next state.
When all nodes have reported the next state, then the transaction proceeds to the next phase. If the membership changes or any node nominates a differing next state during this time, the transaction is aborted. If this does not happen, the transition to the next state is accomplished, and the process is repeated until a final state is achieved. The idea of a generalized synchronization mechanism seems like a very good idea, and one worth emulating in the Linux-HA environment.
Much of the code in heartbeat consists of modules which are invoked through table lookups. These modules provide services which it would be desirable to add dynamic loading so that new modules could be added to heartbeat without restarting the services. In order to ensure reliable heartbeat services in the presence of ill-behaved applications, heartbeat runs locked into memory, and at high priority.
Because of this, it is desirable to minimize the amount of memory which heartbeat used. Replacing the static linking which heartbeat uses with dynamic linking would help in this effort. It is anticipated that heartbeat would benefit from dynamically loading at least the authentication methods, heartbeat media drivers, and STONITH implementations. At this point in time, the implementation of dynamic loading is being tested. For two-node systems, it is often desirable to have a resource which can be used as a quorum resource, so that one can guarantee that only one of two partitions of a cluster can be active at a time.
Since Linux-HA systems are intended to achieve very low deployment costs, it is undesirable to add a third node solely for the purpose of breaking ties. As a result, it would be desirable to allow relatively unintelligent devices which are already present on the customer's site to act as pseudo-cluster members.
For these devices to participate as members, a new class of membership would be added to heartbeat : ping membership.
Whenever the local system would send out its heartbeat, a ping packet would be sent to the pseudo-member. Whenever a ping response is received, it would be translated into a heartbeat message. The result of this is that such devices could effectively act as tie-breakers in the case of 2-node quorum systems. Candidates for such devices include switches, routers, and ethernet-accessible intelligent power controllers or other pingable devices.
There are problems potentially associated with this approach: It is possible through ARP cache problems for example for each of two nodes to be able to communicate with a common endpoint, yet be unable to communicate with each other. At this time, an implementation of this technique has been prototyped and further research will be done to see if there is a variant on this technique which would be helpful in solving these difficulties.
Heartbeat 's current cluster manager was originally prototyped to demonstrate heartbeat. It is unsophisticated and very limited in its function. However, the introduction of the heartbeat API opens up the possibility of providing a "real" cluster manager, or a series of them. It is expected that heartbeat will drop its primitive cluster management facility in favor of external cluster management.
As a result, this current implementation is not discussed here. The previous sections describe the positive reasons why the design decisions were made without significant references being made to the corresponding costs or disadvantages.
This section will explore these costs, and comment on the design of these key areas. Some of the areas addressed here were pointed out by the readers of the linux-ha-dev mailing list.
Initially, the heartbeat code was implemented directly on top of the serial device. This seemed worth trying, so it was implemented. Unfortunately, there were several problems which resulted. In a small percentage of cases, PPP would not start at all, and had to be killed and restarted, sometimes on both ends. Even when it does start correctly, PPP can take up to seven seconds to start.
This makes hangs slow to detect, and delays starting up the cluster. Sometimes, for no apparent reason, PPP would stop transmitting in one direction for no apparent reason and with no obvious symptoms. These bugs and behaviors in PPP make it a poor choice for use in highly reliable systems. These problems exist today, and have existed for more than a year in the Linux PPP implementation.
The workarounds for all these problems make the PPP transport module in heartbeat about twice as large and complex as the corresponding code for any other medium, in addition to being unreliable. Although the heartbeat code has proven quite robust, various people have asked questions about its size.
This breaks down to lines of commented source like this: lines for core function, lines for messaging functions, for authentication, for parsing configuration files, lines for handling different transport media over half of which is PPP code , for the heartbeat API. At this point, it seems to be eminently maintainable. The recently-added ability to dynamically load modules will minimize memory usage while allowing for more growth in capabilities. It has proven to be quite simple to add new heartbeat media types, authentication types, message types and features to heartbeat.
Much of the code is table-driven, and is overall quite straightforward and simple to extend and change. Indeed, one of the unexpected problems associated with writing this paper has been that many things have changed and been implemented while it was being written, causing it to have to be updated continually.
One of the concerns which been expressed concerning the design of heartbeat is that its combination of ASCII message format makes for verbose heartbeat messages.
The concern is specifically that it might become a bandwidth hog as cluster sizes grow. The formula for computing bandwidth used by heartbeat for N nodes on an unswitched network is as follows:.
If a cluster has nodes with these other characteristics, then the B hb for such a system is 1. This is approximately 1. It is clear from this calculation that fears about heartbeat bandwidth consumption are unfounded for realistic-sized clusters. On the other hand, it is also clear from this calculation that this same bandwidth would significantly overwhelm a normal PC serial connection.
Although released versions of heartbeat have had a few bugs, they have largely exhibited themselves consistently on system startup or not all. The result of this is that heartbeat has proven itself to be quite reliable in actual field usage.
The current heartbeat protocol guarantees that packets are delivered to every active node, or that the client is notified of the death of the nodes to which it isn't delivered subject to resource limitations. However, these packets are not guaranteed to be delivered in any particular order, nor is any flow control provided.
The packet delivery order problem is relatively easily solvable should that prove desirable. The flow control issue is not expected to be a problem in the domain for which this protocol is designed high-availability control messages.
However, if a client were sufficiently ill-behaved it is possible that it could exhaust packet retransmission facilities, resulting in a packet not being delivered. Because it was designed from the ground up to operate in the cracker-rich internet environment as an open source Linux package, it is one of the more security-conscious high-availability implementations available.
Although it makes no attempt to encrypt data because of repressive US laws on encryption, it does make good use of strong authentication protocols. One of the most interesting and curious criticisms of heartbeat is that it has been too successful.
What was meant by this was that heartbeat solved a wide-enough class of problems sufficiently well that there was little motivation to create an alternative solution, even though heartbeat itself was quite limited.
In particular, the original heartbeat API was incapable of supporting a sophisticated cluster management infrastructure, so that until the new API was added, it was impossible to go beyond two nodes in the cluster. Now that this API is available, it is possible to write a better cluster management services. Now, heartbeat 's past success can now serve as a springboard for future enhancements and greater usefulness rather than serving as a source of criticism.
Is heartbeat misnamed? Because of the fact that it treats providing heartbeat services as a subcase of cluster communications, some have said that heartbeat is misnamed. It is not simply a heartbeat mechanism, but is best thought of as a robust low-level cluster communications mechanism which provides notification when nodes join and leave the communication channel.
In this sense, the heartbeat could perhaps even be thought of as a side-effect of the reliable communications protocol. Heartbeat 's technique of providing heartbeats as an integral part of a cluster communications channel has proven straightforward and to implement and maintain.
Be carefull!!! I have done exactly same entries in my ha. Any idea how to correct it. Please help? I am using haproxy to route traffic to both servers from the VIP's. Only issue I have found is that if both nodes go off.
It can be a bit of pain to the service heartbeat start to kick in again. Anyone explain why happens. Firstly, this was a great tutorial, thanks. I had trouble starting the heartbeat service using this node directive syntax in the ha. I am using centos 5. This article is really great. I followed the instruction and everything worked smoothly on centos 5.
Both statements have same meanings to hearbeat, perhaps i don't know why error generated. Resources I am using are as follow: CentOS-5 as master-node fedora as slave-node hearbeat 2. So, please guide me regarding this issue. It would be of great help. Reply me on [email protected]. But on each node, it doesn't have eth0 interface. Heartbeat is running fine but it was not able to bring up the resource when i manually try to bring up the resource.
Maybe heartbeat cannot find the gawk command. Heartbeat need the which command to find those commands on your system. First of all ensure that you have configured virtual IP on both of ur nodes primary and secondary. How can I configure heartbeat so that it will pass control to second node if apache in first node fails? When I shut down node1 it switch control to node2. But if apache only apche not heartbeat stopped in first node, it will not pass control to second node.
One thing not mentioned here and something that may save someone a few hours is to make sure that there is no Firewall configured that might be blocking UDP on port When this occurs it is not apparent what is going wrong and the the HA setup immediately goes into a split brain scenario. Its quite frustrating as your installation and configuration will be correct.
This has the benefit of allowing the reaction times to be much quicker and for having services such as httpd and mysqld etc be configured for startup on reboot, irrespective of the actions of heartbeat.
My problem is that my httpd server is not running if I am binding it on virtual ip address, it shows the error:. If I enable httpd to listen on all interface heartbeat is running as expected.
Please correct me if I am wrong anywhere. I have properly installed and configured Heartbeat heartbeat I have question as I stop heartbeat on node01 it automatically shift to node If i stop node02 it should automatically shift to node01 but it doesnot. I need help regarding this As I stop Heartbeat on Node01 it automatically shift to Node02 but vice versa it does not work, means if i stop heartbeat on Node02 it should failover to Node01, how can I do this. The master listed in the haresources file holds all the resources until a failover, at which time the slave takes over.
When set to off this option will prevent the master node from re-acquiring cluster resources after a failover. As per the doc I did the configuration and it is working fine. But when i stopped httpd service on node01 HA is not able to switch to node2's httpd. If any of the service failed it show be able to switch to next server. Yes, it's not free but I've just had it with wasting time with open source. It actually doesnot work better with Gridlock, it is just that you have no clue what you are doing.
0コメント