mirror_corosync/man/openais_overview.8

.\"/*
.\" * Copyright (c) 2005 MontaVista Software, Inc.
.\" *
.\" * All rights reserved.
.\" *
.\" * Author: Steven Dake (sdake@mvista.com)
.\" *
.\" * This software licensed under BSD license, the text of which follows:
.\" * 
.\" * Redistribution and use in source and binary forms, with or without
.\" * modification, are permitted provided that the following conditions are met:
.\" *
.\" * - Redistributions of source code must retain the above copyright notice,
.\" *   this list of conditions and the following disclaimer.
.\" * - Redistributions in binary form must reproduce the above copyright notice,
.\" *   this list of conditions and the following disclaimer in the documentation
.\" *   and/or other materials provided with the distribution.
.\" * - Neither the name of the MontaVista Software, Inc. nor the names of its
.\" *   contributors may be used to endorse or promote products derived from this
.\" *   software without specific prior written permission.
.\" *
.\" * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
.\" * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
.\" * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
.\" * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
.\" * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
.\" * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
.\" * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
.\" * THE POSSIBILITY OF SUCH DAMAGE.
.\" */
.TH OPENAIS_OVERVIEW 8 2005-06-08 "openais Man Page" "Openais Programmer's Manual"
.SH OVERVIEW
The openais project is a project to implement a production quality "Revised BSD"
licensed implementation of the most recent SA Forum's Application Interface
Specification.  The Application Interface Specification is a software API and
policies which are used to develop applications that maintain service during
faults.  The API consists of Availability Management Framework (AMF) which
provides application failover, Cluster Membership (CLM), Checkpointing (CKPT),
Eventing (EVT), Messaging (MSG), and Distributed Locking (DLOCK).

Currently Messaging and Distributed Locking are unimplemented.

Faults occur for various reasons:
.PP
* Application Faults
.PP
* Middleware Faults
.PP
* Operating System Faults
.PP
* 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
AIS. AIS can mask many types of faults in applications, middleware,
operating systems, or even hardware by providing a simple framework
for allowing developers to create redundant applications. These redundant
applications can be distributed over multiple nodes such that if any one
node faults, another node can recover.

Application programmers develop applications to periodically record their
state using the checkpointing service. When an active application fails,
a standby application recovers the state of the application. This
technique, called stateful application failover, provides the fundamental
difference between openais and other systems that have come before it.
With stateful application failover, the end-application user doesn't
have to reload the application or redial a telephone. The full state
is recorded, so the end-application user sees no interruption in service.

Because programmers can now distribute applications across multiple
processes or nodes, a mechanism must exist for them to communicate.
This mechanism is provided by two services. The event service provides
a publish/subscribe model for events. The messaging service provides
end to end messaging. Finally a mechanism to synchronize access is
provided by the distributed lock service. 

The openais project also provides a group messaging toolkit called EVS.
The EVS service implements a messaging model known as Extended Virtual
Synchrony.  This model allows one sender to transmit to many receivers.
Certain guarantees are provided for message and membership delivery
which make virtual synchrony ideal for developing distributed applications.

.SH QUICKSTART
The openais executive must be configured.  In the directory conf in the
source distribution are several files that must be copied to the /etc/ais
directory.  If openais is packaged by a distro, this may be complete.

The directory contains the file openais.conf.  Please read the openais.conf(5)
man page for details on the configuration options.  The openais project will
work out of the box with the default configuration options, although the
administrator may desire different options.

An user and group of the name "ais" must be added to the system.  If openais
is packaged from a distro, this step should already be completed.
This can be achieved by executing:

[root@slickdeal root]# adduser ais -g ais

The openais executive uses cryptographic techniques to ensure authenticity
and privacy of the messages.  In order for openais 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# ais-keygen
openais authentication key generator.
.PP
Gathering 1024 bits for key from /dev/random.
.PP
Writing openais key to /etc/ais/authkey.
.PP

After this operation, a private key will be in the file /etc/ais/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/ais/authkey

If a message "Invalid digest" appears from the openais executive, the keys
are not consistent between processors.

Finally run the openais executive.  If openais 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 openais must be enabled.

After running aisexec, a list of all processors IP addresses running the ais
executive and configured on the same multicast address will appear.  If they
don't appear, there may be a problem with multicast in the distro or hardware.
If this happens, participation in the openais mailing list may help solve the
problem.  The email address is openais@lists.osdl.org.

.SH USING LIBRARIES
The openais AIS libraries have header files which must be included in the
developer's application.  Once the header file is included, the developer can
reference the AIS interfaces.

The openais project recommends to distros to place include files in
/usr/include/openais.  The following include lines must be added to
the application to use each of the following services: 

#include <openais/saClm.h> For the Cluster Membership B.01.01 service.
.PP
#include <openais/saCkpt.h> For the Checkpointing B.01.01 service.
.PP
#include <openais/saEvt.h> For the Eventing B.01.01 service.
.PP
#include <openais/ais_amf.h> For the AMF A.01.01 service.
.PP

The openais project recommends to distros to place library files in
/usr/lib.  The following link lines must be added to the LDFLAGS section
of the makefile.

-lsaClm For the Cluster Membership B.01.01 service
.PP
-lsaCkpt For the Checkpointing B.01.01 service
.PP
-lsaEvt For the Eventing B.01.01 service
.PP
-lsaAmf For the AMF A.01.01 service
.PP
-lais Specify this to get access to all AIS libraries without specifying
each library individually.

.SH ARCHITECTURE
The AIS libraries are a thin IPC interface to the openais executive.  The
openais executive provides services for the SA Forum AIS libraries as well
as the EVS library.

The openais 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.

.SH SECURITY
The openais executive encrypts all messages sent over the network using the
SOBER-128 stream cipher.  The openais executive uses HMAC and SHA1 to
authenticate all messages.  The openais executive library uses SOBER-128
as a pseudo random number generator.  The EVS library feeds the PRNG using
the /dev/random Linux device.
.PP
.SH BUGS
The openais libraries are not particularly compliant with every aspect of the
SA Forum's AIS specification.  The APIs themselves are consistent, but some of
the return values and other details are not quite right yet.  The project does
intend to be fully compliant with SAF specifications in 2005.

The AMF that is currently available is AMF A.01.01.  The rest of the services
are of the B.01.01 specification.  This is a limitation for those developers that
desire AMF B.01.01.  The project intends to resolve this inconsistently in 2005.

The openais project does not currently implement the messaging service or
distributed locking service.
.SH "SEE ALSO"
.BR openais.conf (5),
.BR evs_overview (8)
.PP