repmgr/doc/repmgrd-configuration.sgml

<chapter id="repmgrd-configuration">

  <indexterm>
    <primary>repmgrd</primary>
    <secondary>configuration</secondary>
  </indexterm>

  <title>repmgrd configuration</title>

  <para>
    <application>repmgrd</application> is a daemon which runs on each PostgreSQL node,
    monitoring the local node, and (unless it's the primary node) the upstream server
    (the primary server or with cascading replication, another standby) which it's
    connected to.
  </para>
  <para>
    <application>repmgrd</application> can be configured to provide failover
    capability in case the primary upstream node becomes unreachable, and/or
    provide monitoring data to the &repmgr; metadatabase.
  </para>

  <sect1 id="repmgrd-basic-configuration">
    <title>repmgrd basic configuration</title>

    <para>
      To use <application>repmgrd</application>, its associated function library <emphasis>must</emphasis> be
      included in <filename>postgresql.conf</filename> with:

      <programlisting>
        shared_preload_libraries = 'repmgr'</programlisting>
    </para>
    <para>
      Changing this setting requires a restart of PostgreSQL; for more details see
      the <ulink url="https://www.postgresql.org/docs/current/static/runtime-config-client.html#GUC-SHARED-PRELOAD-LIBRARIES">PostgreSQL documentation</ulink>.
    </para>

    <sect2 id="repmgrd-automatic-failover-configuration">
      <title>automatic failover configuration</title>
      <para>
        If using automatic failover, the following <application>repmgrd</application> options *must* be set in
        <filename>repmgr.conf</filename> :
        <programlisting>
          failover=automatic
          promote_command='/usr/bin/repmgr standby promote -f /etc/repmgr.conf --log-to-file'
          follow_command='/usr/bin/repmgr standby follow -f /etc/repmgr.conf --log-to-file --upstream-node-id=%n'</programlisting>
      </para>
      <para>
        Adjust file paths as appropriate; we recomment specifying the full path to the &repmgr; binary.
      </para>
      <para>
        Note that the <literal>--log-to-file</literal> option will cause
        output generated by the &repmgr; command, when executed by <application>repmgrd</application>,
        to be logged to the same destination configured to receive log output for <application>repmgrd</application>.
        See <filename><ulink url="https://raw.githubusercontent.com/2ndQuadrant/repmgr/master/repmgr.conf.sample">repmgr.conf.sample</ulink></filename>
        for further <application>repmgrd</application>-specific settings.
      </para>
      <para>
        When <varname>failover</varname> is set to <literal>automatic</literal>, upon detecting failure
        of the current  primary, <application>repmgrd</application> will execute one of:
      </para>
      <itemizedlist spacing="compact" mark="bullet">
        <listitem>
          <simpara>
            <varname>promote_command</varname> (if the current server is to become the new primary)
          </simpara>
        </listitem>
        <listitem>
          <simpara>
            <varname>follow_command</varname> (if the current server needs to follow another server which has
            become the new primary)
          </simpara>
        </listitem>
      </itemizedlist>
      <note>
        <para>
          These commands can be any valid shell script which results in one of these
          two actions happening, but if &repmgr;'s <command>standby follow</command> or
          <command>standby promote</command>
          commands are not executed (either directly as shown here, or from a script which
          performs other actions), the &repmgr; metadata will not be updated and
          &repmgr; will no longer function reliably.
        </para>
      </note>

      <para>
        The <varname>follow_command</varname> should provide the <literal>--upstream-node-id=%n</literal>
        option to <command>repmgr standby follow</command>; the <literal>%n</literal> will be replaced by
        <application>repmgrd</application> with the ID of the new primary node. If this is not provided, &repmgr;
        will attempt to determine the new primary by itself, but if the
        original primary comes back online after the new primary is promoted, there is a risk that
        <command>repmgr standby follow</command> will result in the node continuing to follow
        the original primary.
      </para>
    </sect2>

    <sect2 id="repmgrd-service-configuration">
      <indexterm>
        <primary>repmgrd</primary>
        <secondary>PostgreSQL service configuration</secondary>
      </indexterm>
      <title>PostgreSQL service configuration</title>
      <para>
        If using automatic failover, currently <application>repmgrd</application> will need to execute
        <link linkend="repmgr-standby-follow"><command>repmgr standby follow</command></link>
        to restart PostgreSQL on standbys to have them follow a new primary.
      </para>
      <para>
        To ensure this happens smoothly, it's essential to provide the appropriate system/service restart
        command appropriate to your operating system via <varname>service_restart_command</varname>
        in <filename>repmgr.conf</filename>. If you don't do this, <application>repmgrd</application>
        will default to using <command>pg_ctl</command>, which can result in unexpected problems,
        particularly on <application>systemd</application>-based systems.
      </para>
      <para>
        For more details, see <xref linkend="configuration-service-commands">.
      </para>
    </sect2>

    <sect2 id="repmgrd-monitoring-configuration">
      <indexterm>
        <primary>repmgrd</primary>
        <secondary>monitoring configuration</secondary>
      </indexterm>
      <title>Monitoring configuration</title>
      <para>
        To enable monitoring, set:
        <programlisting>
          monitoring_history=yes</programlisting>
        in <filename>repmgr.conf</filename>.
      </para>
      <para>
        The default monitoring interval is 2 seconds; this value can be explicitly set using:
        <programlisting>
          monitor_interval_secs=&lt;seconds&gt;</programlisting>
        in <filename>repmgr.conf</filename>.
      </para>
      <para>
        For more details on monitoring, see <xref linkend="repmgrd-monitoring">.
      </para>
    </sect2>

  </sect1>

 <sect1 id="repmgrd-connection-settings">
 <title>repmgrd connection settings</title>
 <para>
  In addition to the &repmgr; configuration settings, parameters in the
  <varname>conninfo</varname> string influence how &repmgr; makes a network connection to
  PostgreSQL. In particular, if another server in the replication cluster
  is unreachable at network level, system network settings will influence
  the length of time it takes to determine that the connection is not possible.
 </para>
 <para>
  In particular explicitly setting a parameter for <literal>connect_timeout</literal>
  should be considered; the effective minimum value of <literal>2</literal>
  (seconds) will ensure that a connection failure at network level is reported
  as soon as possible, otherwise depending on the system settings (e.g.
  <varname>tcp_syn_retries</varname> in Linux) a delay of a minute or more
  is possible.
 </para>
 <para>
  For further details on <varname>conninfo</varname> network connection
  parameters, see the
  <ulink url="https://www.postgresql.org/docs/current/static/libpq-connect.html#LIBPQ-PARAMKEYWORDS">PostgreSQL documentation</ulink>.
 </para>
 </sect1>



 <sect1 id="repmgrd-log-rotation">
   <indexterm>
     <primary>log rotation</primary>
     <secondary>repmgrd</secondary>
   </indexterm>

  <title>repmgrd log rotation</title>
  <para>
   To ensure the current <application>repmgrd</application> logfile
   (specified in <filename>repmgr.conf</filename> with the parameter
   <option>log_file</option> does not grow indefinitely, configure your
   system's <command>logrotate</command> to regularly rotate it.
  </para>
  <para>
   Sample configuration to rotate logfiles weekly with retention for
   up to 52 weeks and rotation forced if a file grows beyond 100Mb:
   <programlisting>
    /var/log/postgresql/repmgr-9.6.log {
        missingok
        compress
        rotate 52
        maxsize 100M
        weekly
        create 0600 postgres postgres
    }</programlisting>
  </para>
 </sect1>
</chapter>