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COROS...ERVIEW(7) Corosync Cluster Engine Programmer's Manual COROS...ERVIEW(7) NAME corosync_overview - Corosync overview OVERVIEW The corosync project's purpose is to implement and support a production quality Revised BSD licensed implementation of a high performance low over- head high availability development toolkit. Faults occur for various reasons: * Application Faults * Middleware Faults * Operating System Faults * Hardware Faults The major focus of high availability in the past has been to mask hardware faults. Faults in other components of the system have gone unsolved until Corosync. Corosync is designed for applications to replicate their state to multiple processors, with the actual limit determined by factors such as CPU performance, network latency, and network bandwidth. The processors all contain a replica of the application state. The corosync project provides a group message API called CPG. The project developers recommend CPG be used for most applications. The CPG service implements a closed group messaging model presenting extended virtual syn- chrony guarantees. To manage conditions where the process executing the CPG application ex- change fails, we provide the Simple Availability Manager (sam) to provide simple application restart. QUICKSTART The corosync executive must be configured. In the directory conf in the source distribution are several files that must be copied to the /etc/coro- sync directory. If corosync is packaged by a distro, this may be complete. The directory contains the file corosync.conf. Please read the coro- sync.conf(5) man page for details on the configuration options. The coro- sync project will work out of the box with the default configuration op- tions, although the administrator may desire different options. The corosync executive uses cryptographic techniques to ensure authenticity and privacy of the messages. In order for corosync to be secure and oper- ate, a private key must be generated and shared to all processors. First generate the key on one of the nodes: unix# corosync-keygen Corosync Cluster Engine Authentication key generator. Gathering 2048 bits for key from /dev/urandom. Writing corosync key to /etc/corosync/authkey. After this operation, a private key will be in the file /etc/corosync/au- thkey. This private key must be copied to every processor in the cluster. If the private key isn't the same for every node, those nodes with non- matching private keys will not be able to join the same configuration. Copy the key to some security transportable storage or use ssh to transmit the key from node to node. Then install the key with the command: unix#: install -D --group=0 --owner=0 --mode=0400 /path_to_authkey/authkey /etc/corosync/authkey If a message "Invalid digest" appears from the corosync executive, the keys are not consistent between processors. Finally run the corosync executive. If corosync is packaged from a distro, it may be set to start on system start. It may also be turned off by de- fault in which case the init script for corosync must be enabled. USING LIBRARIES The corosync libraries have header files which must be included in the de- veloper's application. Once the header file is included, the developer can reference the corosync interfaces. The corosync project recommends that distros place include files in /usr/include/corosync. IPv6 The corosync project supports both IPv4 and IPv6 network addresses. When using knet as the transport each link should have the same IP family, but different links can have different families (eg link 0 could be all IPv4, and link 1 all IPv6). When using UDP/UDPU the single link should use the same family on all nodes. To configure a host for IPv6, use the ifconfig program to add interfaces: box20: ifconfig eth0 add fec0::1:a800:4ff:fe00:20/64 box30: ifconfig eth0 add fec0::1:a800:4ff:fe00:30/64 If the /64 is not specified, a route for the IPv6 network will not be con- figured which will cause significant problems. Make sure a route is avail- able for IPv6 traffic. ARCHITECTURE The corosync libraries are a thin IPC interface to the corosync executive. The corosync executive implements the functionality of the corosync APIs for distributed computing. The corosync executive uses the Totem extended virtual synchrony protocol. The advantage to the end user is excellent performance characteristics and a proven protocol with excellent reliability. This protocol connects the processors in a configuration together so they may communicate. SECURITY The corosync executive optionally encrypts and signs all messages sent over the network. For more details see crypto_model, crypto_hash and crypto_ci- pher options in the corosync.conf(5). If membership messages can be captured by intruders, it is possible to exe- cute a denial of service attack on the cluster. In this scenario, the cluster is likely already compromised and a DoS attack is the least of the administration's worries. The security in corosync does not offer perfect forward secrecy because the keys are reused. It may be possible for an intruder to determine the shared key by capturing packets in an automated fashion. No such automated attack has been published as of yet. In this scenario, the cluster is likely already compromised to allow the long-term capture of transmitted data. For security reasons, the corosync executive binary should NEVER be setuid or setgid in the filesystem. BUGS None that are known. SEE ALSO corosync.conf(5), corosync-keygen(8), corosync_quorumtool(8), corosync_cfg- tool(8), corosync_cpgtool(8), corosync_cmaptool(8), cpg_overview(3), sam_overview(3) corosync Man Page 2018-11-13 COROS...ERVIEW(7)
NAME | OVERVIEW | QUICKSTART | USING LIBRARIES | IPv6 | ARCHITECTURE | SECURITY | BUGS | SEE ALSO
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