Provided by: corosync_2.3.5-3ubuntu2.3_amd64 
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 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 hardware 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
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 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.
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/corosync directory. If
corosync is packaged by a distro, this may be complete.
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 configuration options, 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 operate, 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 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 processor 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 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 default 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 developer's
application. Once the header file is included, the developer can reference the corosync
interfaces.
The corosync project recommends to distros to place include files in
/usr/include/corosync.
IPv6
The corosync project supports both IPv4 and IPv6 network addresses. The entire cluster
must use either IPv4 or IPv6 for the cluster communication mechanism. In order to use
IPv6, IPv6 addresses must be specified 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 mcastaddr: ff05::1
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 configured which
will cause significant problems. Make sure a route is available 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 coming.
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.
ENVIRONMENT VARIABLES
The corosync executive process uses four environment variables during startup. If these
environment variables are not set, defaults will be used.
COROSYNC_MAIN_CONFIG_FILE
This specifies the fully qualified path to the corosync configuration file.
The default is /etc/corosync/corosync.conf.
COROSYNC_TOTEM_AUTHKEY_FILE
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.
SECURITY
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
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), cpg_overview(8), sam_overview(8)