COROSYNC_OVERVIEW(Corosync Cluster Engine Programmer's ManCOROSYNC_OVERVIEW(8)NAMEcorosync_overview - Corosync overview
The corosync project's purpose is to implement and support a production
quality Revised BSD licensed implementation of a high performance low
overhead 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 hard‐
ware faults. Faults in other components of the system have gone
unsolved until Corosync. Corosync is designed for applications to
replicate their state to up to 16 processors. The processors all con‐
tain 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 synchrony guarantees.
To manage conditions where the process executing the CPG application
exchange fails, we provide the Simple Availability Manager (sam) to
provide simple application restart.
The corosync executive must be configured. In the directory conf in
the source distribution are several files that must be copied to the
/etc/corosync directory. If corosync is packaged by a distro, this may
The directory contains the file corosync.conf. Please read the
corosync.conf(5) man page for details on the configuration options.
The corosync project will work out of the box with the default configu‐
ration options, although the administrator may desire different
The corosync executive uses cryptographic techniques to ensure authen‐
ticity and privacy of the messages. In order for corosync to be secure
and operate, a private key must be generated and shared to all proces‐
First generate the key on one of the nodes:
Corosync Cluster Engine Authentication key generator.
Gathering 1024 bits for key from /dev/random.
Press keys on your keyboard to generate entropy.
Writing corosync key to /etc/corosync/authkey.
After this operation, a private key will be in the file
/etc/corosync/authkey. This private key must be copied to every pro‐
cessor in the cluster. If the private key isn't the same for every
node, those nodes with nonmatching 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 com‐
unix#: install -D --group=0 --owner=0 --mode=0400
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 default in which case the init script for corosync must be
The corosync libraries have header files which must be included in the
developer's application. Once the header file is included, the devel‐
oper can reference the corosync interfaces.
The corosync project recommends to distros to place include files in
The corosync project supports both IPv4 and IPv6 network addresses.
The entire cluster must use either IPv4 or IPv6 for the cluster commu‐
nication mechanism. In order to use IPv6, IPv6 addresses must be spec‐
ified in the bindnetaddr and mcastaddr fields in the configuration
file. The nodeid field must also be set.
An example of this is: nodeid: 2 bindnetaddr: fec0::1:a800:4ff:fe00:20
To configure a host for IPv6, use the ifconfig program to add inter‐
faces: 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
configured which will cause significant problems. Make sure a route is
available for IPv6 traffic.
The corosync libraries are a thin IPC interface to the corosync execu‐
tive. The corosync executive implements the functionality of the
corosync APIs for distributed coming.
The corosync executive uses the Totem extended virtual synchrony proto‐
col. The advantage to the end user is excellent performance character‐
istics and a proven protocol with excellent reliability. This protocol
connects the processors in a configuration together so they may commu‐
The corosync executive process uses four environment variables during
startup. If these environment variables are not set, defaults will be
This specifies the fully qualified path to the corosync configu‐
The default is /etc/corosync/corosync.conf.
This specifies the fully qualified path to the shared key used
to authenticate and encrypt data used within the Totem protocol.
The default is /etc/corosync/authkey.
The corosync executive optionally encrypts all messages sent over the
network using the AES-128 cipher. The corosync executive uses HMAC and
SHA1 to authenticate all messages. The corosync executive library uses
NSS as a pseudo random number generator.
If membership messages can be captured by intruders, it is possible to
execute 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 by capturing
packets in an automated fashion to determine the shared key. 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
For security reasons, the corosync executive binary should NEVER be
setuid or setgid in the filesystem.
None that are known.
SEE ALSOcorosync.conf(5), corosync-keygen(8), cpg_overview(8), sam_overview(8)corosync Man Page 2012-02-13 COROSYNC_OVERVIEW(8)