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doc: improve configuration documentation
With special attention to setting service commands, and extra special mention of "pg_ctlcluster" for Debian/Ubuntu users.
This commit is contained in:
Ian Barwick
@@ -1,63 +1,145 @@
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<chapter id="repmgrd-configuration">
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<indexterm>
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<primary>repmgrd</primary>
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<secondary>configuration</secondary>
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</indexterm>
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<indexterm>
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<primary>repmgrd</primary>
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<secondary>configuration</secondary>
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</indexterm>
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<title>repmgrd configuration</title>
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<para>
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To use <application>repmgrd</application>, its associated function library must be
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included in <filename>postgresql.conf</filename> with:
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<title>repmgrd configuration</title>
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<programlisting>
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shared_preload_libraries = 'repmgr'</programlisting>
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</para>
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<para>
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Changing this setting requires a restart of PostgreSQL; for more details see
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the <ulink url="https://www.postgresql.org/docs/current/static/runtime-config-client.html#GUC-SHARED-PRELOAD-LIBRARIES">PostgreSQL documentation</ulink>.
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</para>
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<para>
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Additionally the following <application>repmgrd</application> options *must* be set in
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<filename>repmgr.conf</filename> (adjust configuration file locations as appropriate):
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<programlisting>
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failover=automatic
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promote_command='repmgr standby promote -f /etc/repmgr.conf --log-to-file'
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follow_command='repmgr standby follow -f /etc/repmgr.conf --log-to-file --upstream-node-id=%n'</programlisting>
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</para>
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<para>
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Note that the <literal>--log-to-file</literal> option will cause
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output generated by the &repmgr; command, when executed by <application>repmgrd</application>,
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to be logged to the same destination configured to receive log output for <application>repmgrd</application>.
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See <filename>repmgr.conf.sample</filename> for further <application>repmgrd</application>-specific settings.
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</para>
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<para>
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When <varname>failover</varname> is set to <literal>automatic</literal>, upon detecting failure
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of the current primary, <application>repmgrd</application> will execute either
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<varname>promote_command</varname> (if the current server is to become the new primary) or
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<varname>follow_command</varname> (if the current serverneeds to follow another server which has
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become the new primary.
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</para>
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<note>
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<para>
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These commands can be any valid shell script which results in one of these
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two actions happening, but if &repmgr;'s <command>standby follow</command> or
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<command>standby promote</command>
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commands are not executed (either directly as shown here, or from a script which
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performs other actions), the &repmgr; metadata will not be updated and
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&repmgr; will no longer function reliably.
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</para>
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</note>
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<para>
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<application>repmgrd</application> is a daemon which runs on each PostgreSQL node,
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monitoring the local node, and (unless it's the primary node) the upstream server
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(the primary server or with cascading replication, another standby) which it's
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connected to.
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</para>
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<para>
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<application>repmgrd</application> can be configured to provide failover
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capability in case the primary upstream node becomes unreachable, and/or
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provide monitoring data to the &repmgr; metadatabase.
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</para>
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<para>
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The <varname>follow_command</varname> should provide the <literal>--upstream-node-id=%n</literal>
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option to <command>repmgr standby follow</command>; the <literal>%n</literal> will be replaced by
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<application>repmgrd</application> with the ID of the new primary node. If this is not provided, &repmgr;
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will attempt to determine the new primary by itself, but if the
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original primary comes back online after the new primary is promoted, there is a risk that
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<command>repmgr standby follow</command> will result in the node continuing to follow
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the original primary.
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</para>
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<sect1 id="repmgrd-basic-configuration">
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<title>repmgrd basic configuration</title>
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<para>
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To use <application>repmgrd</application>, its associated function library <emphasis>must</emphasis> be
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included in <filename>postgresql.conf</filename> with:
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<programlisting>
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shared_preload_libraries = 'repmgr'</programlisting>
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</para>
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<para>
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Changing this setting requires a restart of PostgreSQL; for more details see
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the <ulink url="https://www.postgresql.org/docs/current/static/runtime-config-client.html#GUC-SHARED-PRELOAD-LIBRARIES">PostgreSQL documentation</ulink>.
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</para>
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<sect2 id="repmgrd-automatic-failover-configuration">
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<title>automatic failover configuration</title>
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<para>
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If using automatic failover, the following <application>repmgrd</application> options *must* be set in
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<filename>repmgr.conf</filename> :
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<programlisting>
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failover=automatic
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promote_command='/usr/bin/repmgr standby promote -f /etc/repmgr.conf --log-to-file'
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follow_command='/usr/bin/repmgr standby follow -f /etc/repmgr.conf --log-to-file --upstream-node-id=%n'</programlisting>
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</para>
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<para>
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Adjust file paths as appropriate; we recomment specifying the full path to the &repmgr; binary.
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</para>
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<para>
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Note that the <literal>--log-to-file</literal> option will cause
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output generated by the &repmgr; command, when executed by <application>repmgrd</application>,
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to be logged to the same destination configured to receive log output for <application>repmgrd</application>.
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See <filename><ulink url="https://raw.githubusercontent.com/2ndQuadrant/repmgr/master/repmgr.conf.sample">repmgr.conf.sample</ulink></filename>
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for further <application>repmgrd</application>-specific settings.
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</para>
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<para>
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When <varname>failover</varname> is set to <literal>automatic</literal>, upon detecting failure
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of the current primary, <application>repmgrd</application> will execute one of:
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</para>
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<itemizedlist spacing="compact" mark="bullet">
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<listitem>
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<simpara>
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<varname>promote_command</varname> (if the current server is to become the new primary)
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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<varname>follow_command</varname> (if the current server needs to follow another server which has
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become the new primary)
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</simpara>
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</listitem>
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</itemizedlist>
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<note>
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<para>
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These commands can be any valid shell script which results in one of these
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two actions happening, but if &repmgr;'s <command>standby follow</command> or
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<command>standby promote</command>
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commands are not executed (either directly as shown here, or from a script which
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performs other actions), the &repmgr; metadata will not be updated and
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&repmgr; will no longer function reliably.
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</para>
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</note>
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<para>
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The <varname>follow_command</varname> should provide the <literal>--upstream-node-id=%n</literal>
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option to <command>repmgr standby follow</command>; the <literal>%n</literal> will be replaced by
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<application>repmgrd</application> with the ID of the new primary node. If this is not provided, &repmgr;
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will attempt to determine the new primary by itself, but if the
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original primary comes back online after the new primary is promoted, there is a risk that
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<command>repmgr standby follow</command> will result in the node continuing to follow
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the original primary.
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</para>
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</sect2>
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<sect2 id="repmgrd-service-configuration">
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<indexterm>
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<primary>repmgrd</primary>
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<secondary>PostgreSQL service configuration</secondary>
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</indexterm>
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<title>PostgreSQL service configuration</title>
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<para>
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If using automatic failover, currently <application>repmgrd</application> will need to execute
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<link linkend="repmgr-standby-follow"><command>repmgr standby follow</command></link>
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to restart PostgreSQL on standbys to have them follow a new primary.
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</para>
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<para>
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To ensure this happens smoothly, it's essential to provide the appropriate system/service restart
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command appropriate to your operating system via <varname>service_restart_command</varname>
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in <filename>repmgr.conf</filename>. If you don't do this, <application>repmgrd</application>
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will default to using <command>pg_ctl</command>, which can result in unexpected problems,
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particularly on <application>systemd</application>-based systems.
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</para>
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<para>
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For more details, see <xref linkend="configuration-service-commands">.
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</para>
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</sect2>
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<sect2 id="repmgrd-monitoring-configuration">
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<indexterm>
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<primary>repmgrd</primary>
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<secondary>monitoring configuration</secondary>
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</indexterm>
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<title>Monitoring configuration</title>
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<para>
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To enable monitoring, set:
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<programlisting>
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monitoring_history=yes</programlisting>
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in <filename>repmgr.conf</filename>.
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</para>
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<para>
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The default monitoring interval is 2 seconds; this value can be explicitly set using:
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<programlisting>
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monitor_interval_secs=<seconds></programlisting>
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in <filename>repmgr.conf</filename>.
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</para>
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<para>
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For more details on monitoring, see <xref linkend="repmgrd-monitoring">.
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</para>
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</sect2>
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</sect1>
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<sect1 id="repmgrd-connection-settings">
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<title>repmgrd connection settings</title>
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@@ -84,86 +166,19 @@
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</sect1>
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<sect1 id="repmgrd-service-command">
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<sect1 id="repmgrd-log-rotation">
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<indexterm>
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<primary>service commands</primary>
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<primary>log rotation</primary>
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<secondary>repmgrd</secondary>
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</indexterm>
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<title>repmgrd and service commands</title>
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<para>
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By default, &repmgr; will use <application>pg_ctl</application> to
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stop, start, restart, reloadthe PostgreSQL cluster.
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However, if installed from a package, particularly under
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<application>pg_ctl</application>, it's advisable to specify
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the appropriate service commands to perform these options.
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</para>
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<para>
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To do this, specify the appropriate command for each action
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in <filename>repmgr.conf</filename> using the following configuration
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parameters:
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<programlisting>
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service_start_command
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service_stop_command
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service_restart_command
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service_reload_command</programlisting>
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</para>
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<note>
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<para>
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It's also possible to specify a <varname>service_promote_command</varname>;
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this overrides any value contained in the setting <varname>promote_command</varname>.
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This is intended for systems which provide a package-level promote command,
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such as Debian's <application>pg_ctlcluster</application>.
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</para>
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</note>
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<para>
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To confirm which command &repmgr; will execute for each action, use
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<command>repmgr node service --list --action=...</command>, e.g.:
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<programlisting>
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repmgr -f /etc/repmgr.conf node service --list --action=stop
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repmgr -f /etc/repmgr.conf node service --list --action=start
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repmgr -f /etc/repmgr.conf node service --list --action=restart
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repmgr -f /etc/repmgr.conf node service --list --action=reload</programlisting>
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</para>
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<para>
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These commands will be executed by the system user which &repmgr; runs as (usually <literal>postgres</literal>)
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and will probably require passwordless sudo access to be able to execute the command.
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</para>
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<para>
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For example, using <application>systemd</application> on CentOS 7, the service commands can be
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set as follows:
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<programlisting>
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service_start_command = 'sudo systemctl start postgresql-9.6'
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service_stop_command = 'sudo systemctl stop postgresql-9.6'
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service_restart_command = 'sudo systemctl restart postgresql-9.6'</programlisting>
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and <filename>/etc/sudoers</filename> should be set as follows:
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<programlisting>
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Defaults:postgres !requiretty
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postgres ALL = NOPASSWD: /usr/bin/systemctl stop postgresql-9.6, \
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/usr/bin/systemctl start postgresql-9.6, \
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/usr/bin/systemctl restart postgresql-9.6</programlisting>
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</para>
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<note>
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<para>
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If using <application>systemd</application>, ensure you have <varname>RemoteIPC</varname> set to <literal>off</literal>.
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See the <ulink url="https://wiki.postgresql.org/wiki/Systemd">systemd</ulink>
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entry in the <ulink url="https://wiki.postgresql.org/wiki/Main_Page">PostgreSQL wiki</ulink> for details.
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</para>
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</note>
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</sect1>
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<sect1 id="repmgrd-log-rotation">
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<title>repmgrd log rotation</title>
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<para>
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To ensure the current <application>repmgrd</application> logfile does not grow
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indefinitely, configure your system's <command>logrotate</command> to
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regularly rotate it.
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To ensure the current <application>repmgrd</application> logfile
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(specified in <filename>repmgr.conf</filename> with the parameter
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<option>log_file</option> does not grow indefinitely, configure your
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system's <command>logrotate</command> to regularly rotate it.
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</para>
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<para>
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Sample configuration to rotate logfiles weekly with retention for
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