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Add functionality to "pause" repmgrd

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In some circumstances, e.g. while performing a switchover, it is essential
that repmgrd does not take any kind of failover action, as this will put
the cluster into an incorrect state.

Previously it was necessary to stop repmgrd on all nodes (or at least
those nodes which repmgrd would consider as promotion candidates), however
this is a cumbersome and potentially risk-prone operation, particularly if the
replication cluster contains more than a couple of servers.

To prevent this issue from occurring, this patch introduces the ability
to "pause" repmgrd on all nodes wth a single command ("repmgr daemon pause")
which notifies repmgrd not to take any failover action until the node
is "unpaused" ("repmgr daemon unpause").

"repmgr daemon status" provides an overview of each node and whether repmgrd
is running, and if so whether it is paused.

"repmgr standby switchover" has been modified to automatically pause repmgrd
while carrying out the switchover.

See documentation for further details.
This commit is contained in:
Ian Barwick
2018-09-27 16:42:10 +09:00
parent fce3c02760
commit 2491b8ae52
27 changed files with 1943 additions and 121 deletions
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33
doc/repmgr-standby-switchover.sgml
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@@ -35,6 +35,10 @@
&repmgr; will attempt to check for potential issues but cannot guarantee
a successful switchover.
</para>
<para>
&repmgr; will refuse to perform the switchover if an exclusive backup is running on
the current primary.
</para>
</note>
<para>
For more details on performing a switchover, including preparation and configuration,
@@ -43,11 +47,14 @@
<note>
<para>
<application>repmgrd</application> should not be active on any nodes while a switchover is being
executed. This restriction may be lifted in a later version.
From <link linkend="release-4.2">repmgr 4.2</link>, &repmgr; will instruct any running
<application>repmgrd</application> instances to pause operations while the switchover
is being carried out, to prevent <application>repmgrd</application> from
unintentionally promoting a node. For more details, see <xref linkend="repmgrd-pausing">.
</para>
<para>
&repmgr; will not perform the switchover if an exclusive backup is running on the current primary.
Users of &repmgr; versions prior to 4.2 should ensure that <application>repmgrd</application>
is not running on any nodes while a switchover is being executed.
</para>
</note>
@@ -61,8 +68,9 @@
<term><option>--always-promote</option></term>
<listitem>
<para>
Promote standby to primary, even if it is behind original primary
(original primary will be shut down in any case).
Promote standby to primary, even if it is behind or has diverged
from the original primary. The original primary will be shut down in any case,
and will need to be manually reintegrated into the replication cluster.
</para>
</listitem>
</varlistentry>
@@ -122,6 +130,21 @@
</listitem>
</varlistentry>
<varlistentry>
<term><option>--repmgrd-no-pause</option></term>
<listitem>
<para>
Don't pause <application>repmgrd</application> while executing a switchover.
</para>
<para>
This option should not be used unless you take steps by other means
to ensure <application>repmgrd</application> is paused or not
running on all nodes.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--siblings-follow</option></term>
<listitem>