1COROSYNC_OVERVIEW(8C)orosync Cluster Engine Programmer's ManuCaOlROSYNC_OVERVIEW(8)
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6 corosync_overview - Corosync overview
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9 The corosync project's purpose is to implement and support a production
10 quality Revised BSD licensed implementation of a high performance low
11 overhead high availability development toolkit.
12 Faults occur for various reasons:
14 * Application Faults
16 * Middleware Faults
18 * Operating System Faults
20 * Hardware Faults
22 The major focus of high availability in the past has been to mask hard‐
24 ware faults. Faults in other components of the system have gone
25 unsolved until Corosync. Corosync is designed for applications to
26 replicate their state to up to 16 processors. The processors all con‐
27 tain a replica of the application state.
28 The corosync project provides a group message API called CPG. The
30 project developers recommend CPG be used for most applications. The
31 CPG service implements a closed group messaging model presenting
32 extended virtual synchrony guarantees.
33 To manage conditions where the process executing the CPG application
35 exchange fails, we provide the Simple Availability Manager (sam) to
36 provide simple application restart.
37
40 The corosync executive must be configured. In the directory conf in
41 the source distribution are several files that must be copied to the
42 /etc/corosync directory. If corosync is packaged by a distro, this may
43 be complete.
44 The directory contains the file corosync.conf. Please read the
46 corosync.conf(5) man page for details on the configuration options.
47 The corosync project will work out of the box with the default configu‐
48 ration options, although the administrator may desire different
49 options.
50 The corosync executive uses cryptographic techniques to ensure authen‐
52 ticity and privacy of the messages. In order for corosync to be secure
53 and operate, a private key must be generated and shared to all proces‐
54 sors.
55 First generate the key on one of the nodes:
57 unix# corosync-keygen
59 Corosync Cluster Engine Authentication key generator.
60 Gathering 1024 bits for key from /dev/random.
61 Press keys on your keyboard to generate entropy.
62 Writing corosync key to /etc/corosync/authkey.
63 After this operation, a private key will be in the file
65 /etc/corosync/authkey. This private key must be copied to every pro‐
66 cessor in the cluster. If the private key isn't the same for every
67 node, those nodes with nonmatching private keys will not be able to
68 join the same configuration.
69 Copy the key to some security transportable storage or use ssh to
71 transmit the key from node to node. Then install the key with the com‐
72 mand:
73 unix#: install -D --group=0 --owner=0 --mode=0400
75 /path_to_authkey/authkey /etc/corosync/authkey
76 If a message "Invalid digest" appears from the corosync executive, the
78 keys are not consistent between processors.
79 Finally run the corosync executive. If corosync is packaged from a
81 distro, it may be set to start on system start. It may also be turned
82 off by default in which case the init script for corosync must be
83 enabled.
84
87 The corosync libraries have header files which must be included in the
88 developer's application. Once the header file is included, the devel‐
89 oper can reference the corosync interfaces.
90 The corosync project recommends to distros to place include files in
92 /usr/include/corosync.
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96 The corosync project supports both IPv4 and IPv6 network addresses.
97 The entire cluster must use either IPv4 or IPv6 for the cluster commu‐
98 nication mechanism. In order to use IPv6, IPv6 addresses must be spec‐
99 ified in the bindnetaddr and mcastaddr fields in the configuration
100 file. The nodeid field must also be set.
101 An example of this is: nodeid: 2 bindnetaddr: fec0::1:a800:4ff:fe00:20
103 mcastaddr: ff05::1
104 To configure a host for IPv6, use the ifconfig program to add inter‐
106 faces: box20: ifconfig eth0 add fec0::1:a800:4ff:fe00:20/64 box30:
107 ifconfig eth0 add fec0::1:a800:4ff:fe00:30/64
108 If the /64 is not specified, a route for the IPv6 network will not be
110 configured which will cause significant problems. Make sure a route is
111 available for IPv6 traffic.
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115 The corosync libraries are a thin IPC interface to the corosync execu‐
116 tive. The corosync executive implements the functionality of the
117 corosync APIs for distributed coming.
118 The corosync executive uses the Totem extended virtual synchrony proto‐
120 col. The advantage to the end user is excellent performance character‐
121 istics and a proven protocol with excellent reliability. This protocol
122 connects the processors in a configuration together so they may commu‐
123 nicate.
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127 The corosync executive process uses four environment variables during
128 startup. If these environment variables are not set, defaults will be
129 used.
130 COROSYNC_MAIN_CONFIG_FILE
133 This specifies the fully qualified path to the corosync configu‐
134 ration file.
135 The default is /etc/corosync/corosync.conf.
137 COROSYNC_TOTEM_AUTHKEY_FILE
140 This specifies the fully qualified path to the shared key used
141 to authenticate and encrypt data used within the Totem protocol.
142 The default is /etc/corosync/authkey.
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147 The corosync executive optionally encrypts all messages sent over the
148 network using the AES-128 cipher. The corosync executive uses HMAC and
149 SHA1 to authenticate all messages. The corosync executive library uses
150 NSS as a pseudo random number generator.
151 If membership messages can be captured by intruders, it is possible to
153 execute a denial of service attack on the cluster. In this scenario,
154 the cluster is likely already compromised and a DOS attack is the least
155 of the administration's worries.
156 The security in corosync does not offer perfect forward secrecy because
158 the keys are reused. It may be possible for an intruder by capturing
159 packets in an automated fashion to determine the shared key. No such
160 automated attack has been published as of yet. In this scenario, the
161 cluster is likely already compromised to allow the long-term capture of
162 transmitted data.
163 For security reasons, the corosync executive binary should NEVER be
165 setuid or setgid in the filesystem.
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169 None that are known.
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173 corosync.conf(5), corosync-keygen(8), cpg_overview(8), sam_overview(8)
174corosync Man Page 2012-02-13 COROSYNC_OVERVIEW(8)