kea/doc/guide/shell.xml

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<chapter id="kea-shell">
  <title>The Kea Shell</title>

  <section id="shell-overview">
    <title>Overview</title>
    <para>Kea 1.2.0 introduced the Control Agent (CA, see <xref linkend="kea-ctrl-agent"/>) that
    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 you want
    to send a command to the CA directly.  The Kea Shell provides a way to do this.  It is a simple
    command-line, scripting-friendly text client that is able connect to the CA, send it commands
    with parameters, retrieve the responses and display them.</para>

    <para>As the primary purpose of the Kea Shell is as a tool in scripting environment,
    it is not interactive. However, with simple tricks it can be run manually.
    </para>
  </section>

  <section id="shell-usage">
    <title>Shell Usage</title>
    <para><command>kea-shell</command> is run as follows:
<screen>
kea-shell [--host hostname] [--port number] [--path path] [--timeout seconds] [--service service-name] [command]
</screen>
    where:
    </para>
    <itemizedlist>
      <listitem>
        <simpara>
          <command>--host <replaceable>hostname</replaceable></command> specifies the hostname
          of the CA. If not specified, "localhost" is used.
        </simpara>
      </listitem>

      <listitem>
        <simpara>
          <command>--port <replaceable>number</replaceable></command> specifies the TCP port
          on which the CA listens. If not specified, 8000 is used.
        </simpara>
      </listitem>

      <listitem>
        <simpara>
          <command>--path <replaceable>path</replaceable></command> specifies
          the path in the URL to connect to. If not specified,
          empty path is used. As CA listens at the empty path
          this parameter is useful only with a reverse proxy.
        </simpara>
      </listitem>

      <listitem>
        <simpara>
          <command>--timeout <replaceable>seconds</replaceable></command> specifies the
          timeout (in seconds) for the connection. If not given, 10 seconds is used.
        </simpara>
      </listitem>

      <listitem>
        <simpara>
          <command>--service <replaceable>service-name</replaceable></command> specifies the
          target of a command. If not given, CA will be used as target.  May be used more
          than once to specify multiple targets.
        </simpara>
      </listitem>


      <listitem>
        <simpara>
          <command>command</command> specifies the command to be sent. If not specified,
          <command>list-commands</command> command is used.
        </simpara>
      </listitem>
    </itemizedlist>

    <para>Other switches are:</para>
    <itemizedlist>
      <listitem>
        <simpara>
          <command>-h</command> prints a help message.
        </simpara>
      </listitem>
      <listitem>
        <simpara>
          <command>-v</command> prints the software version.
        </simpara>
      </listitem>
    </itemizedlist>

    <para>
      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 printed on standard output.
    </para>

    <para>
      For a list of available commands, see <xref linkend="ctrl-channel"/>. Additional commands
      may be provided by hook libraries. If unsure which commands are supported, use the
      <command>list-commands</command> command. It will instruct the CA to return a list of
      all supported commands.
    </para>

    <para>The following shows a simple example of usage:
<screen>
$ <userinput>kea-shell --host 192.0.2.1 --port 8001 --service dhcp4 list-commands</userinput>
^D
</screen>
    After the command line is entered, the program waits for command parameters to be entered.
    Since <command>list-commands</command> does not take any
    arguments, CTRL-D (represented in the above example by "^D") is pressed to indicate end
    of file (and so terminate the parameter input). The Shell will then contact
    the CA and print out the list of available commands returned for the service named <command>dhcp4</command>.
    </para>

    <para>It is envisaged that 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
    (<command> --service </command> parameter hasn't been used), along
    with the parameters specified in param.json. The result will be stored in result.json.
<screen>
$ cat param.json
"filename": "my-config-file.json"
$ <userinput>cat param.json | kea-shell --host 192.0.2.1 config-write > result.json</userinput>
</screen>
    </para>

    <para>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
    <command> --path </command> parameter should be used. For instance
    if requests to the "/kea" path are forwarded to the CA this can be used:
<screen>
$ <userinput>kea-shell --host 192.0.2.1 --port 8001 --path kea ...</userinput>
</screen>
    </para>

    <para>Kea Shell requires Python to to be installed on the system. It was 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,
    you must specify <command>--enable-shell</command> to when running "configure" during the
    installation of Kea.</para>

    <para>The Kea Shell is intended to serve more as a demonstration of the RESTful interface
    capabilities (and, perhaps, an illustration for people interested in integrating their
    management evironments with Kea) than as a serious management client. Do not expect it
    to be significantly expanded in the future. It is, and will remain, a simple tool.</para>
    </section>
</chapter>