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<chapter id="admin">
  <title>Kea Database Administration</title>

  <section id="kea-database-version">
    <title>Databases and Database Version Numbers</title>

    <para>
      Kea supports storing leases and host reservations (i.e. static
      assignments of addresses, prefixes and options) in one of
      the several supported databases. As future versions of Kea
      are released, the structure of those databases will change.
      For example, Kea currently only stores lease information
      and host reservations. Future versions of Kea will store
      additional data such as subnet definitions: the database
      structure will need to be updated to accommodate the extra
      information.
    </para>

    <para>
      A given version of Kea expects a particular structure in
      the database and checks for this by examining the version of
      database it is using.  Separate version numbers are maintained for
      backend databases, independent of the version of Kea itself. It
      is possible that the backend database version will stay the same
      through several Kea revisions: similarly, it is possible that the
      version of backend database may go up several revisions during a
      Kea upgrade.  Versions for each database are independent, so an
      increment in the MySQL database version does not imply an increment
      in that of PostgreSQL.
    </para>

    <para>
      Backend versions are specified in
      a <replaceable>major.minor</replaceable> format. The minor
      number is increased when there are backward compatible changes
      introduced.  For example, the addition of a new index. It is
      desirable, but not mandatory to apply such a change; you
      can run on older database version if you want to. (Although, in
      the example given, running without the new index may be at the
      expense of a performance penalty.) On the other hand, the major
      number is increased when an incompatible change is introduced,
      for example an extra column is added to a table. If you try to
      run Kea software on a database that is too old (as signified by
      mismatched backend major version number), Kea will refuse to run:
      administrative action will be required to upgrade the database.
    </para>
  </section>

  <section id="kea-admin">
    <title>The kea-admin Tool</title>

    <para>
      To manage the databases, Kea provides the
      <command>kea-admin</command> tool. It is able to initialize
      a new database, check its version number, perform a
      database upgrade, and dump lease data to a text file.
    </para>

    <para>
      <command>kea-admin</command> takes two mandatory
      parameters: <command>command</command> and
      <command>backend</command>. Additional, non-mandatory options
      may be specified. Currently supported commands are:

      <itemizedlist>
        <listitem>
          <simpara>
            <command>lease-init</command> &mdash;
            Initializes a new lease database. This is useful during a new
            Kea installation. The database is initialized to the
            latest version supported by the version of the software being
            installed.
          </simpara>
        </listitem>

        <listitem>
          <simpara>
            <command>lease-version</command> &mdash;
            Reports the lease database version number. This is
            not necessarily equal to the Kea version number as
            each backend has its own versioning scheme.
          </simpara>
        </listitem>

        <listitem>
          <simpara>
            <command>lease-upgrade</command> &mdash;
            Conducts a lease database upgrade. This is useful when
            upgrading Kea.
          </simpara>
        </listitem>

        <listitem>
          <simpara>
            <command>lease-dump</command> &mdash;
            Dumps the contents of the lease database (for MySQL, PostgreSQL or
            CQL backends) to a CSV (comma separated values) text file. The first
            line of the file contains the column names.  This is meant to be
            used as a diagnostic tool, so it provides a portable, human-readable
            form of the lease data.
          </simpara>
        </listitem>
      </itemizedlist>

      <command>backend</command> specifies the backend type. Currently
      supported types are:

      <itemizedlist>
        <listitem>
          <simpara>
            <command>memfile</command> &mdash; Lease information is
            stored on disk in a text file.
          </simpara>
        </listitem>

        <listitem>
          <simpara>
            <command>mysql</command> &mdash;
            Lease information is stored in a MySQL relational database.
          </simpara>
        </listitem>

        <listitem>
          <simpara>
            <command>pgsql</command> &mdash;
            Lease information is stored in a PostgreSQL relational database.
          </simpara>
        </listitem>

        <listitem>
          <simpara>
            <command>cql</command> &mdash;
            Lease information is stored in a CQL database.
          </simpara>
        </listitem>

      </itemizedlist>

      Additional parameters may be needed, depending on your setup
      and specific operation: username, password and database name or
      the directory where specific files are located. See the appropriate
      manual page for details (<command>man 8 kea-admin</command>).
    </para>
  </section>

  <section id="supported-databases">
    <title>Supported Databases</title>

    <para>The following table presents the capabilities of available
    backends. Please refer to the specific sections dedicated to each backend to
    better understand their capabilities and limitations. Choosing the right
    backend may be essential for success or failure of your deployment.</para>

    <para>
      <table frame="all" id="backends">
        <title>List of available backends</title>
        <tgroup cols='2'>
          <colspec colname='feature'/>
          <colspec colname='memfile'/>
          <colspec colname='mysql'/>
          <colspec colname='pgsql'/>
          <colspec colname='cql'/>
          <thead>
            <row>
              <entry>Feature</entry>
              <entry>Memfile</entry>
              <entry>MySQL</entry>
              <entry>PostgreSQL</entry>
              <entry>CQL(Cassandra)</entry>
            </row>
          </thead>
          <tbody>

            <row>
              <entry>Status</entry>
              <entry>Stable</entry>
              <entry>Stable</entry>
              <entry>Stable</entry>
              <entry>Experimental</entry>
            </row>

            <row>
              <entry>Data format</entry>
              <entry>CSV file</entry>
              <entry>SQL RMDB</entry>
              <entry>SQL RMDB</entry>
              <entry>NoSQL database (CQL)</entry>
            </row>

            <row>
              <entry>Leases</entry>
              <entry>yes</entry>
              <entry>yes</entry>
              <entry>yes</entry>
              <entry>yes</entry>
            </row>

            <row>
              <entry>Host Reservations</entry>
              <entry>no</entry>
              <entry>yes</entry>
              <entry>yes</entry>
              <entry>no</entry>
            </row>

            <row>
              <entry>Options defined on per host basis</entry>
              <entry>no</entry>
              <entry>yes</entry>
              <entry>yes</entry>
              <entry>no</entry>
            </row>

          </tbody>
          </tgroup>
       </table>
    </para>

    <section>
      <title>memfile</title>

      <para>
        The memfile backend is able to store lease information, but is not able to
        store host reservation details: these must be stored in the configuration
        file. (There are no plans to add a host reservations storage capability to
        this backend.)
      </para>

      <para>
        No special initialization steps are necessary
        for the memfile backend.  During the first run, both
        <command>kea-dhcp4</command> and <command>kea-dhcp6</command>
        will create an empty lease file if one is not
        present. Necessary disk write permission is required.
      </para>

      <section id="memfile-upgrade">
        <title>Upgrading Memfile Lease Files from an Earlier Version of Kea</title>
        <para>
        There are no special steps required to upgrade memfile lease files
        from an earlier version of Kea to a new version of Kea.

        During startup the servers will check the schema version of the lease
        files against their own.  If there is a mismatch, the servers will
        automatically launch the LFC process to convert the files to the
        server's schema version.  While this mechanism is primarily meant to
        ease the process of upgrading to newer versions of Kea, it can also
        be used for downgrading should the need arise.  When upgrading, any
        values not present in the original lease files will be assigned
        appropriate default values.  When downgrading, any data present in
        the files but not in the server's schema will be dropped.

        If you wish to convert the files manually, prior to starting the
        servers you may do so by running the LFC process yourself.
        See <xref linkend="kea-lfc"/> for more information.
        </para>
      </section>
      <!-- @todo: document lease file upgrades once they are implemented in kea-admin -->
    </section>

    <section>
      <title>MySQL</title>

      <para>
        MySQL is able to store leases, host reservations and options defined on
        a per host basis. This section can be safely ignored
        if you chose to store the data in other backends.
      </para>

      <section id="mysql-database-create">
        <title>First Time Creation of the MySQL Database</title>

        <para>
          If you are setting the MySQL database for the first time,
          you need to create the database area within MySQL and set up
          the MySQL user ID under which Kea will access the database.
          This needs to be done manually: <command>kea-admin</command>
          is not able to do this for you.
        </para>

        <para>
          To create the database:

          <orderedlist>
            <listitem>
              <para>
                Log into MySQL as "root":
<screen>
$ <userinput>mysql -u root -p</userinput>
Enter password:
mysql>
</screen>
              </para>
            </listitem>

            <listitem>
              <para>
                Create the MySQL database:
<screen>
mysql> <userinput>CREATE DATABASE <replaceable>database-name</replaceable>;</userinput>
</screen>
                (<replaceable>database-name</replaceable> is the name
                you have chosen for the database.)
              </para>
            </listitem>

            <listitem>
              <para>
                Create the user under which Kea will access the database
                (and give it a password), then grant it access to the
                database tables:
<screen>
mysql> <userinput>CREATE USER '<replaceable>user-name</replaceable>'@'localhost' IDENTIFIED BY '<replaceable>password</replaceable>';</userinput>
mysql> <userinput>GRANT ALL ON <replaceable>database-name</replaceable>.* TO '<replaceable>user-name</replaceable>'@'localhost';</userinput>
</screen>
                (<replaceable>user-name</replaceable> and
                <replaceable>password</replaceable> are the user ID
                and password you are using to allow Keas access to the
                MySQL instance. All apostrophes in the command lines
                above are required.)
              </para>
            </listitem>

            <listitem>
              <para>
                At this point, you may elect to create the database
                tables. (Alternatively, you can exit MySQL and create
                the tables using the <command>kea-admin</command> tool,
                as explained below.)  To do this:
<screen>
mysql> <userinput>CONNECT <replaceable>database-name</replaceable>;</userinput>
mysql> <userinput>SOURCE <replaceable>path-to-kea</replaceable>/share/kea/scripts/mysql/dhcpdb_create.mysql</userinput>
</screen>
                (<replaceable>path-to-kea</replaceable> is the
                location where you installed Kea.)
              </para>
            </listitem>

            <listitem>
              <para>
                Exit MySQL:
<screen>
mysql> <userinput>quit</userinput>
Bye
$
</screen>
              </para>
            </listitem>
          </orderedlist>
        </para>

        <para>
          If you elected not to create the tables in step 4, you can do
          so now by running the <command>kea-admin</command> tool:
<screen>
$ <userinput>kea-admin lease-init mysql -u <replaceable>database-user</replaceable> -p <replaceable>database-password</replaceable> -n <replaceable>database-name</replaceable></userinput>
</screen>
          (Do not do this if you did create the tables in step 4.)
          <command>kea-admin</command> implements rudimentary checks:
          it will refuse to initialize a database that contains any
          existing tables. If you want to start from scratch, you
          must remove all data manually. (This process is a manual
          operation on purpose to avoid possibly irretrievable mistakes
          by <command>kea-admin</command>.)
        </para>
      </section>

      <section id="mysql-upgrade">
        <title>Upgrading a MySQL Database from an Earlier Version of Kea</title>

        <para>
          Sometimes a new Kea version may use newer database schema, so
          there will be a need to upgrade the existing database. This can
          be done using the <command>kea-admin lease-upgrade</command>
          command.
        </para>

        <para>
          To check the current version of the database, use the following command:
<screen>
$ <userinput>kea-admin lease-version mysql -u <replaceable>database-user</replaceable> -p <replaceable>database-password</replaceable> -n <replaceable>database-name</replaceable></userinput>
</screen>
          (See <xref linkend="kea-database-version"/> for a discussion
          about versioning.)  If the version does not match the minimum
          required for the new version of Kea (as described in the
          release notes), the database needs to be upgraded.
        </para>

        <para>
          Before upgrading, please make sure that the database is
          backed up.  The upgrade process does not discard any data but,
          depending on the nature of the changes, it may be impossible
          to subsequently downgrade to an earlier version.  To perform
          an upgrade, issue the following command:
<screen>
$ <userinput>kea-admin lease-upgrade mysql -u <replaceable>database-user</replaceable> -p <replaceable>database-password</replaceable> -n <replaceable>database-name</replaceable></userinput>
</screen>
        </para>
      </section>
    </section> <!-- end of MySQL sections -->

    <section>
      <title>PostgreSQL</title>

      <para>
        A PostgreSQL database must be set up if you want Kea to store
        lease and other information in PostgreSQL. This step can be
        safely ignored if you are using other database backends.
      </para>

      <section id="pgsql-database-create">
        <title>First Time Creation of the PostgreSQL Database</title>

        <para>
          The first task is to create both the lease database and the
          user under which the servers will access it. A number of steps
          are required:

          <orderedlist>
            <listitem>
              <para>
                Log into PostgreSQL as "root":
<screen>
$ <userinput>sudo -u postgres psql postgres</userinput>
Enter password:
postgres=#
</screen>
              </para>
            </listitem>

            <listitem>
              <para>
                Create the database:
<screen>
postgres=#<userinput> CREATE DATABASE <replaceable>database-name</replaceable>;</userinput>
CREATE DATABASE
postgres=#
</screen>
                (<replaceable>database-name</replaceable> is the name
                you have chosen for the database.)
              </para>
            </listitem>

            <listitem>
              <para>
                Create the user under which Kea will access the database
                (and give it a password), then grant it access to the
                database:
<screen>
postgres=#<userinput> CREATE USER <replaceable>user-name</replaceable> WITH PASSWORD '<replaceable>password</replaceable>';</userinput>
CREATE ROLE
postgres=#<userinput> GRANT ALL PRIVILEGES ON DATABASE <replaceable>database-name</replaceable> TO <replaceable>user-name</replaceable>;</userinput>
GRANT
postgres=#
</screen>
              </para>
            </listitem>

            <listitem>
              <para>
                Exit PostgreSQL:
<screen>
postgres=# <userinput>\q</userinput>
Bye
$
</screen>
              </para>
            </listitem>

            <listitem>
              <para>
                At this point you are ready to create the database tables.
                This can be done using the <command>kea-admin</command> tool
                as explained in the next section (recommended), or manually.
                To create the tables manually enter the following command.
                Note that PostgreSQL will prompt you to enter the new user's
                password you specified in Step 3. When the command completes
                you will be returned to the shell prompt. You should see output
                similar to following:
<screen>
$ <userinput>psql -d <replaceable>database-name</replaceable> -U <replaceable>user-name</replaceable> -f <replaceable>path-to-kea</replaceable>/share/kea/scripts/pgsql/dhcpdb_create.pgsql</userinput>
Password for user <replaceable>user-name</replaceable>:
CREATE TABLE
CREATE INDEX
CREATE INDEX
CREATE TABLE
CREATE INDEX
CREATE TABLE
START TRANSACTION
INSERT 0 1
INSERT 0 1
INSERT 0 1
COMMIT
CREATE TABLE
START TRANSACTION
INSERT 0 1
COMMIT
$
</screen>
                (<replaceable>path-to-kea</replaceable> is the location
                where you installed Kea.)
              </para>

              <para>
                If instead you encounter an error like:
<screen>
psql: FATAL:  no pg_hba.conf entry for host "[local]", user "<replaceable>user-name</replaceable>", database "<replaceable>database-name</replaceable>", SSL off
</screen>
                ... you will need to alter the PostgreSQL configuration.
                Kea uses password authentication when connecting to
                the database and must have the appropriate entries
                added to PostgreSQL's pg_hba.conf file.  This file is
                normally located in the primary data directory for your
                PostgreSQL server. The precise path may vary but the
                default location for PostgreSQL 9.3 on Centos 6.5 is:
                <filename>/var/lib/pgsql/9.3/data/pg_hba.conf</filename>.
              </para>

              <para>
                Assuming Kea is running on the same host as PostgreSQL,
                adding lines similar to following should be sufficient to
                provide password-authenticated access to Kea's database:
<screen>
local   <replaceable>database-name</replaceable>    <replaceable>user-name</replaceable>                                 password
host    <replaceable>database-name</replaceable>    <replaceable>user-name</replaceable>          127.0.0.1/32           password
host    <replaceable>database-name</replaceable>    <replaceable>user-name</replaceable>          ::1/128                password
</screen>
              </para>

              <para>
                These edits are primarily intended as a starting point
                not a definitive reference on PostgreSQL administration or
                database security.  Please consult your PostgreSQL user
                manual before making these changes as they may expose
                other databases that you run.  It may be necessary to
                restart PostgreSQL in order for these changes to take effect.
              </para>
            </listitem>
          </orderedlist>
        </para>
      </section>

      <section>
        <title>Initialize the PostgreSQL Database Using kea-admin</title>
        <para>
          If you elected not to create the tables manually, you can do
          so now by running the <command>kea-admin</command> tool:
<screen>
$ <userinput>kea-admin lease-init pgsql -u <replaceable>database-user</replaceable> -p <replaceable>database-password</replaceable> -n <replaceable>database-name</replaceable></userinput>
</screen>
          Do not do this if you already created the tables in manually.
          <command>kea-admin</command> implements rudimentary checks:
          it will refuse to initialize a database that contains any
          existing tables. If you want to start from scratch, you
          must remove all data manually. (This process is a manual
          operation on purpose to avoid possibly irretrievable mistakes
          by <command>kea-admin</command>.)
        </para>
      </section>
      <section id="pgsql-upgrade">
        <title>Upgrading a PostgreSQL Database from an Earlier Version of Kea</title>
        <para>
          The PostgreSQL database schema can be upgraded using the same tool and
          commands as described in <xref linkend="mysql-upgrade"/>, with the
          exception that the "pgsql" database backend type must be used in
          the commands.
        </para>
        <para>
          Use the following command to check the current schema version:
<screen>
$ <userinput>kea-admin lease-version pgsql -u <replaceable>database-user</replaceable> -p <replaceable>database-password</replaceable> -n <replaceable>database-name</replaceable></userinput>
</screen>
          Use the following command to perform an upgrade:
<screen>
$ <userinput>kea-admin lease-upgrade pgsql -u <replaceable>database-user</replaceable> -p <replaceable>database-password</replaceable> -n <replaceable>database-name</replaceable></userinput>
</screen>
        </para>
      </section>
    </section> <!-- end of PostgreSQL sections -->

    <section>
      <title>CQL (Cassandra)</title>

      <para>
        Cassandra, or Cassandra Query Language (CQL), is the newest backend
        added to Kea. Since it was added recently and has not undergone as much
        testing as other backends, it is considered experimental: please use
        with caution. The CQL backend is currently able to store leases only. The
        ability to store host reservations will likely be added some time in the
        future.
      </para>

      <para>
        The CQL database must be properly set up if you want Kea to store
        information in CQL. This section can be safely ignored if you chose to
        store the data in other backends.
      </para>

    <section id="cql-database-create">
      <title>First Time Creation of the Cassandra Database</title>

      <para>
        If you are setting up the CQL database for the first time, you need to
        create the keyspace area within CQL. This needs to be done manually:
        <command>kea-admin</command> is not able to do this for you.
      </para>

      <para>
        To create the database:
        <orderedlist>
          <listitem>
            <para>
              Export CQLSH_HOST environment variable:
<screen>
$ <userinput>export CQLSH_HOST=localhost</userinput>
</screen>
              </para>
            </listitem>
          <listitem>
            <para>
              Log into CQL:
<screen>
$ <userinput>cqlsh</userinput>
cql>
</screen>
              </para>
            </listitem>

          <listitem>
            <para>
              Create the CQL keyspace:
<screen>
cql> <userinput>CREATE KEYSPACE keyspace-name WITH replication = {'class' : 'SimpleStrategy','replication_factor' : 1};</userinput>
</screen>
              (<replaceable>keyspace-name</replaceable> is the name you have
              chosen for the keyspace)
            </para>
          </listitem>

         <listitem>
            <para>
              At this point, you may elect to create the database tables.
              (Alternatively, you can exit CQL and create the tables using the
              <command>kea-admin</command> tool, as explained below)  To do this:
<screen>
<userinput>cqslh -k <replaceable>keyspace-name</replaceable> -f <replaceable>path-to-kea</replaceable>/share/kea/scripts/cql/dhcpdb_create.cql</userinput>
</screen>
              (<replaceable>path-to-kea</replaceable> is the location where you
              installed Kea)
            </para>
          </listitem>
        </orderedlist>
      </para>

      <para>
        If you elected not to create the tables in step 4, you can do
        so now by running the <command>kea-admin</command> tool:
<screen>
$ <userinput>kea-admin lease-init cql -n <replaceable>database-name</replaceable></userinput>
</screen>
        (Do not do this if you did create the tables in step 4.)
        <command>kea-admin</command> implements rudimentary checks:
        it will refuse to initialize a database that contains any
        existing tables. If you want to start from scratch, you
        must remove all data manually. (This process is a manual
        operation on purpose to avoid possibly irretrievable mistakes
        by <command>kea-admin</command>)
      </para>
    </section>

    <section id="cql-upgrade">
      <title>Upgrading a CQL Database from an Earlier Version of Kea</title>

      <para>
        Sometimes a new Kea version may use newer database schema, so
        there will be a need to upgrade the existing database. This can
        be done using the <command>kea-admin lease-upgrade</command>
        command.
      </para>

      <para>
        To check the current version of the database, use the following command:
<screen>
$ <userinput>kea-admin lease-version cql -n <replaceable>database-name</replaceable></userinput>
</screen>
        (See <xref linkend="kea-database-version"/> for a discussion
        about versioning)  If the version does not match the minimum
        required for the new version of Kea (as described in the
        release notes), the database needs to be upgraded.
      </para>

      <para>
        Before upgrading, please make sure that the database is
        backed up.  The upgrade process does not discard any data but,
        depending on the nature of the changes, it may be impossible
        to subsequently downgrade to an earlier version.  To perform
        an upgrade, issue the following command:
<screen>
$ <userinput>kea-admin lease-upgrade cql -n <replaceable>database-name</replaceable></userinput>
</screen>
      </para>
    </section>
  </section> <!-- end of CQL sections -->

    <section>
      <title>Using Read-Only Databases with Host Reservations</title>
      <para>If a read-only database is used for storing host reservations,
      Kea must be explicitly configured to operate on the database in
      read-only mode.
      Sections <xref linkend="read-only-database-configuration4"/> and
      <xref linkend="read-only-database-configuration6"/> describe when
      such configuration may be required and how to configure Kea to
      operate using a read-only host database.
      </para>
    </section>

    <section>
      <title>Limitations Related to the use of SQL Databases</title>


      <section>
        <title>Year 2038 issue</title>
        <para>
          The lease expiration time is stored in the SQL database for each lease
          as a timestamp value. Kea developers observed that MySQL database doesn't
          accept timestamps beyond 2147483647 seconds (maximum signed 32-bit number)
          from the beginning of the epoch. At the same time, some versions of PostgreSQL
          do accept greater values but the value is altered when it is read back.
          For this reason the lease database backends put the restriction for the
          maximum timestamp to be stored in the database, which is equal to the
          maximum signed 32-bit number. This effectively means that the current
          Kea version can't store the leases which expiration time is later than
          2147483647 seconds since the beginning of the epoch (around year 2038).
          This will be fixed when the database support for longer timestamps
          is available.
        </para>
      </section>

      <section>
        <title>Server Terminates when Database Connection is Lost</title>
        <para>
          If Kea is configured to use an external database it opens a connection
          to the database and requires that this connection is not interrupted.
          When the database connection breaks, e.g. as a result of SQL server
          restart, DHCP servers will terminate indicating a fatal error. In such
          a case, the system administrator is required to start the database and
          then "manually" start Kea to resume the service.
        </para>

        <para>
          Although the engineering team is planning to implement some form of
          reconnect mechanism in the future, this will mostly be applicable in
          cases when the database service is restarted and the connection
          down time is relatively short. The DHCP server can't provide its
          service as long as the database is down, because it can't store
          leases being assigned to the clients. The server will have to
          reject any DHCP messages as long as the connection is down and
          terminate if the reconnection attempt fails multiple times.
        </para>

        <para>
          Because the database connection is critical for the operation of the
          DHCP service, the current behavior is to terminate when that
          connection is unavailable to indicate that server is in inconsistent
          state and can't serve clients.
        </para>
      </section>

    </section>

  </section> <!-- End of Database sections -->

</chapter>
