20. The Kea Shell¶
20.1. Overview of the Kea Shell¶
Kea 1.2.0 introduced the Control Agent (CA, see The Kea Control Agent), which provides a RESTful control interface over HTTP. That API is typically expected to be used by various IPAMs and similar management systems. Nevertheless, there may be cases when an administrator wants to send a command to the CA directly, and the Kea shell provides a way to do this. It is a simple command-line, scripting-friendly, text client that is able to connect to the CA, send it commands with parameters, retrieve the responses, and display them.
As the primary purpose of the Kea shell is as a tool in a scripting environment, it is not interactive. However, following simple guidelines it can be run manually.
20.2. Shell Usage¶
kea-shell is run as follows:
$ kea-shell [--host hostname] [--port number] [--path path] [--timeout seconds] [--service service-name] [command]
--host hostnamespecifies the hostname of the CA. If not specified, “localhost” is used.
--port numberspecifies the TCP port on which the CA listens. If not specified, 8000 is used.
--path pathspecifies the path in the URL to connect to. If not specified, an empty path is used. As the CA listens at the empty path, this parameter is useful only with a reverse proxy.
--timeout secondsspecifies the timeout (in seconds) for the connection. If not given, 10 seconds is used.
--service service-namespecifies the target of a command. If not given, the CA will be used as the target. May be used more than once to specify multiple targets.
commandspecifies the command to be sent. If not specified, the
list-commandscommand is used.
Other switches are:
-h- prints a help message.
-v- prints the software version.
Once started, the shell reads parameters for the command from standard input, which are expected to be in JSON format. When all have been read, the shell establishes a connection with the CA using HTTP, sends the command, and awaits a response. Once that is received, it is displayed on standard output.
For a list of available commands, see Management API;
additional commands may be provided by hooks libraries. For a list of
all supported commands from the CA, use the
The following shows a simple example of usage:
$ kea-shell --host 192.0.2.1 --port 8001 --service dhcp4 list-commands ^D
After the command line is entered, the program waits for command
parameters to be entered. Since
list-commands does not take any
arguments, CTRL-D (represented in the above example by “^D”) is pressed
to indicate end-of-file and terminate the parameter input. The shell
then contacts the CA and prints out the list of available commands
returned for the service named
It is envisaged that the Kea shell will be most frequently used in
scripts; the next example shows a simple scripted execution. It sends
the command “config-write” to the CA (the
--service parameter has not
been used), along with the parameters specified in param.json. The
result will be stored in result.json.
$ cat param.json "filename": "my-config-file.json" $ cat param.json | kea-shell --host 192.0.2.1 config-write > result.json
When a reverse proxy is used to de-multiplex requests to different
servers, the default empty path in the URL is not enough, so the
--path parameter should be used. For instance, if requests to the
“/kea” path are forwarded to the CA this can be used:
$ kea-shell --host 192.0.2.1 --port 8001 --path kea ...
The Kea shell requires Python to to be installed on the system. It has been
tested with Python 2.7 and various versions of Python 3, up to 3.5.
Since not every Kea deployment uses this feature and there are
deployments that do not have Python, the Kea shell is not enabled by
default. To use it, specify
--enable-shell when running “configure”
during the installation of Kea. When building on Debian systems, also
--with-site-packages=... may be useful.
The Kea shell is intended to serve more as a demonstration of the RESTful interface’s capabilities (and, perhaps, an illustration for people interested in integrating their management environments with Kea) than as a serious management client. It is not likely to be significantly expanded in the future; it is, and will remain, a simple tool.