repmgr/doc/repmgr-node-rejoin.sgml

<refentry id="repmgr-node-rejoin">

  <indexterm>
    <primary>repmgr node rejoin</primary>
  </indexterm>

  <refmeta>
    <refentrytitle>repmgr node rejoin</refentrytitle>
  </refmeta>

  <refnamediv>
    <refname>repmgr node rejoin</refname>
    <refpurpose>rejoin a dormant (stopped) node to the replication cluster</refpurpose>
  </refnamediv>

  <refsect1>
    <title>Description</title>
    <para>
      Enables a dormant (stopped) node to be rejoined to the replication cluster.
    </para>
    <para>
      This can optionally use <application>pg_rewind</application> to re-integrate
      a node which has diverged from the rest of the cluster, typically a failed primary.
    </para>

    <tip>
      <para>
        If the node is running and needs to be attached to the current primary, use
        <xref linkend="repmgr-standby-follow">.
      </para>
    </tip>
  </refsect1>


  <refsect1>
    <title>Usage</title>

    <para>
      <programlisting>
      repmgr node rejoin -d '$conninfo'</programlisting>

      where <literal>$conninfo</literal> is the conninfo string of any reachable node in the cluster.
      <filename>repmgr.conf</filename> for the stopped node *must* be supplied explicitly if not
      otherwise available.
    </para>
  </refsect1>

  <refsect1>
    <title>Notes</title>
    <para>
      Currently <command>repmgr node rejoin</command> can only be used to attach
      a standby to the current primary, not another standby.
    </para>
    <para>
      The node must have been shut down cleanly; if this was not the case, it will
      need to be manually started (remove any existing <filename>recovery.conf</filename> file first)
      until it has reached a consistent recovery point, then shut down cleanly.
    </para>
    <tip>
      <para>
        If <application>PostgreSQL</application> is started in single-user mode and
        input is directed from <filename>/dev/null/</filename>, it will perform recovery
        then immediately quit, and will then be in a state suitable for use by
        <application>pg_rewind</application>.
        <programlisting>
          rm -f /var/lib/pgsql/data/recovery.conf
          postgres --single -D /var/lib/pgsql/data/ &lt; /dev/null</programlisting>
      </para>
    </tip>
  </refsect1>

  <refsect1 id="repmgr-node-rejoin-pg-rewind">
    <title>Using <command>pg_rewind</command></title>
    <para>
      <command>repmgr node rejoin</command> can optionally use <command>pg_rewind</command> to re-integrate a
      node which has diverged from the rest of the cluster, typically a failed primary.
      <command>pg_rewind</command> is available in PostgreSQL 9.5 and later.
    </para>
    <note>
      <para>
        <command>pg_rewind</command> *requires* that either <varname>wal_log_hints</varname> is enabled, or that
        data checksums were enabled when the cluster was initialized. See the
        <ulink url="https://www.postgresql.org/docs/current/static/app-pgrewind.html"><command>pg_rewind</command> documentation</ulink> for details.
      </para>
    </note>

    <para>
      To have <command>repmgr node rejoin</command> use <command>pg_rewind</command> if required,
      pass the command line option <literal>--force-rewind</literal>, which will tell &repmgr;
      to execute <command>pg_rewind</command> to ensure the node can be rejoined successfully.
    </para>

    <para>
      Be aware that if <command>pg_rewind</command> is executed and actually performs a
      rewind operation, any configuration files in the PostgreSQL data directory will be
      overwritten with those from the source server.
    </para>
    <para>
      To prevent this happening, provide a comma-separated list of files to retain
      using the <literal>--config-file</literal> command line option; the specified files
      will be archived in a temporary directory (whose parent directory can be specified with
      <literal>--config-archive-dir</literal>) and restored once the rewind operation is
      complete.
    </para>

    <para>
      Example, first using <literal>--dry-run</literal>, then actually executing the
      <literal>node rejoin command</literal>.
    <programlisting>
    $ repmgr node rejoin -f /etc/repmgr.conf -d 'host=node1 dbname=repmgr user=repmgr' \
         --force-rewind --config-files=postgresql.local.conf,postgresql.conf --verbose --dry-run
    NOTICE: using provided configuration file "/etc/repmgr.conf"
    INFO: prerequisites for using pg_rewind are met
    INFO: file "postgresql.local.conf" would be copied to "/tmp/repmgr-config-archive-node1/postgresql.local.conf"
    INFO: file "postgresql.conf" would be copied to "/tmp/repmgr-config-archive-node1/postgresql.local.conf"
    INFO: 2 files would have been copied to "/tmp/repmgr-config-archive-node1"
    INFO: directory "/tmp/repmgr-config-archive-node1" deleted
    INFO: pg_rewind would now be executed
    DETAIL: pg_rewind command is:
      pg_rewind -D '/var/lib/postgresql/data' --source-server='host=node1 dbname=repmgr user=repmgr'</programlisting>
    <programlisting>
    $ repmgr node rejoin -f /etc/repmgr.conf -d 'host=node1 dbname=repmgr user=repmgr' \
         --force-rewind --config-files=postgresql.local.conf,postgresql.conf --verbose
    NOTICE: using provided configuration file "/etc/repmgr.conf"
    INFO: prerequisites for using pg_rewind are met
    INFO: 2 files copied to "/tmp/repmgr-config-archive-node1"
    NOTICE: executing pg_rewind
    NOTICE: 2 files copied to /space/sda1/ibarwick/repmgr-test/node_1/data
    INFO: directory "/tmp/repmgr-config-archive-node1" deleted
    INFO: deleting "recovery.done"
    INFO: setting node 1's primary to node 2
    NOTICE: starting server using "pg_ctl-l /var/log/postgres/startup.log -w -D '/var/lib/pgsql/data' start"
    waiting for server to start.... done
    server started
    NOTICE: NODE REJOIN successful
    DETAIL: node 1 is now attached to node 2</programlisting>
    </para>


  </refsect1>

  <refsect1>
    <title>See also</title>
    <para>
     <xref linkend="repmgr-standby-follow">
    </para>
  </refsect1>
</refentry>