Difference between revisions of "User:Jbroman/Ceo Architecture"

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This is a draft of a document on the architecture of <tt>ceo</tt>.
 
This is a draft of a document on the architecture of <tt>ceo</tt>.
   

Revision as of 11:51, 8 September 2010


This is a draft of a document on the architecture of ceo.

Getting

All of these components are available in source form in the the public/pyceo.git repository. The official Debian packages are on http://debian.csclub.uwaterloo.ca/. This server should be in the APT sources list of all club machines.

Architecture

Overview

The ceo ecosystem consists of the following components:

ceo
a command-line interface to various club-related administation functions
ceod
a Kerberized daemon responsible for executing tasks requiring special access (e.g. creating Kerberos principals or MySQL databases) on behalf of the user
ceoc
a client program used by ceo to send messages to ceod for execution

ceo

ceo is the user interface with which users interact. It is implemented in Python and presents a curses-based menu system (though some features can also be accessed by passing command-line flags). It is installed at /usr/bin/ceo by the ceo-python Debian package.

When launched, users may be prompted for their password. This is used to obtain a Kerberos ticket for the LDAP service if neither a service ticket nor ticket-granting ticket are found in the cache.

The following tasks are completed by creating a request which is relayed by ceoc and executed by ceod on the appropriate machine.

  • Adding new users (members, club reps, clubs) is done on ginseng.
  • Creating MySQL databases is done on caffeine since mysqld is configured to allow only local connections.

The library feature queries a PostgreSQL database; all other functions (at time of writing) are done over LDAP using the user's previously obtained ticket.

The interface itself consists of a series of menus and wizards using urwid which call the appropriate functions in the ceo package (such as ceo.members.create_member).

ceod

ceod is installed at /usr/sbin/ceod by the ceo-daemon package. It is a Kerberized daemon (service principal ceod/hostname@CSCLUB.UWATERLOO.CA) listening on TCP port 9987. Each connection forks a slave ceod process to handle that session.

ceod's basic message format is this (note that network byte order is big-endian, whereas the most common host architectures are little-endian):

Field Data Type Description
msglen 32-bit unsigned integer (network order) Length of the message body, in bytes
msgtype 32-bit unsigned integer (network order) Type of message (MSG_AUTH = 0x8000000, all other values are treated as an op message)
body Raw bytes Body of the message

Clients are expected to authenticate (using MSG_AUTH messages) before attempting to execute operations. Failure to do so will result in the connection being unceremoniously terminated. The body of an authentication message is a GSSAPI (Kerberos) token. These are used according to the Kerberos protocol to authenticate the client to ceod (and vice versa) and establish a session key.

The msgtype of an op message identifies the operation to be run. This is a reference to the appropriate op as defined in a configuration file in /etc/csc/ops. One such file is /etc/csc/ops/adduser:

ginseng adduser root 0x01

The first field here is the host on which the operation should be executed. ceod will not execute an operation that is not configured to execute on the host. The second field is the the op name. The third field is the user/group as which the operation should execute. The fourth field is the msgtype which represents that op.