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Further repmgrd documentation
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Ian Barwick
@@ -46,6 +46,7 @@
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<!ENTITY repmgrd-automatic-failover SYSTEM "repmgrd-automatic-failover.sgml">
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<!ENTITY repmgrd-configuration SYSTEM "repmgrd-configuration.sgml">
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<!ENTITY repmgrd-demonstration SYSTEM "repmgrd-demonstration.sgml">
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<!ENTITY repmgr-primary-register SYSTEM "repmgr-primary-register.sgml">
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<!ENTITY repmgr-primary-unregister SYSTEM "repmgr-primary-unregister.sgml">
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@@ -79,6 +79,7 @@
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<title>Using repmgrd</title>
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&repmgrd-automatic-failover;
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&repmgrd-configuration;
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&repmgrd-demonstration;
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</part>
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<part id="repmgr-command-reference">
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@@ -47,5 +47,28 @@
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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-connection-settings">
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<title>repmgrd connection settings</title>
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<para>
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In addition to the &repmgr; configuration settings, parameters in the
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<varname>conninfo</varname> string influence how &repmgr; makes a network connection to
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PostgreSQL. In particular, if another server in the replication cluster
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is unreachable at network level, system network settings will influence
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the length of time it takes to determine that the connection is not possible.
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</para>
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<para>
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In particular explicitly setting a parameter for <literal>connect_timeout</literal>
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should be considered; the effective minimum value of <literal>2</literal>
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(seconds) will ensure that a connection failure at network level is reported
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as soon as possible, otherwise depending on the system settings (e.g.
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<varname>tcp_syn_retries</varname> in Linux) a delay of a minute or more
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is possible.
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</para>
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<para>
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For further details on <varname>conninfo</varname> network connection
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parameters, see the
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<ulink url="https://www.postgresql.org/docs/current/static/libpq-connect.html#LIBPQ-PARAMKEYWORDS">PostgreSQL documentation</ulink>.
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</para>
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</sect1>
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</chapter>
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96
doc/repmgrd-demonstration.sgml
Normal file
96
doc/repmgrd-demonstration.sgml
Normal file
@@ -0,0 +1,96 @@
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<chapter id="repmgrd-demonstration">
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<title>repmgrd demonstration</title>
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<para>
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To demonstrate automatic failover, set up a 3-node replication cluster (one primary
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and two standbys streaming directly from the primary) so that the cluster looks
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something like this:
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<programlisting>
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$ repmgr -f /etc/repmgr.conf cluster show
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ID | Name | Role | Status | Upstream | Location | Connection string
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----+-------+---------+-----------+----------+----------+--------------------------------------
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1 | node1 | primary | * running | | default | host=node1 dbname=repmgr user=repmgr
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2 | node2 | standby | running | node1 | default | host=node2 dbname=repmgr user=repmgr
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3 | node3 | standby | running | node1 | default | host=node3 dbname=repmgr user=repmgr </programlisting>
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</para>
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<para>
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Start <command>repmgrd</command> on each standby and verify that it's running by examining the
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log output, which at log level <literal>INFO</literal> will look like this:
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<programlisting>
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[2017-08-24 17:31:00] [NOTICE] using configuration file "/etc/repmgr.conf"
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[2017-08-24 17:31:00] [INFO] connecting to database "host=node2 dbname=repmgr user=repmgr"
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[2017-08-24 17:31:00] [NOTICE] starting monitoring of node <literal>node2</literal> (ID: 2)
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[2017-08-24 17:31:00] [INFO] monitoring connection to upstream node "node1" (node ID: 1) </programlisting>
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</para>
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<para>
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Each <command>repmgrd</command> should also have recorded its successful startup as an event:
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<programlisting>
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$ repmgr -f /etc/repmgr.conf cluster event --event=repmgrd_start
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Node ID | Name | Event | OK | Timestamp | Details
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---------+-------+---------------+----+---------------------+-------------------------------------------------------------
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3 | node3 | repmgrd_start | t | 2017-08-24 17:35:54 | monitoring connection to upstream node "node1" (node ID: 1)
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2 | node2 | repmgrd_start | t | 2017-08-24 17:35:50 | monitoring connection to upstream node "node1" (node ID: 1)
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1 | node1 | repmgrd_start | t | 2017-08-24 17:35:46 | monitoring cluster primary "node1" (node ID: 1) </programlisting>
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</para>
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<para>
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Now stop the current primary server with e.g.:
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<programlisting>
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pg_ctl -D /var/lib/postgresql/data -m immediate stop</programlisting>
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</para>
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<para>
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This will force the primary to shut down straight away, aborting all processes
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and transactions. This will cause a flurry of activity in the <command>repmgrd</command> log
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files as each <command>repmgrd</command> detects the failure of the primary and a failover
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decision is made. This is an extract from the log of a standby server (<literal>node2</literal>)
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which has promoted to new primary after failure of the original primary (<literal>node1</literal>).
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<programlisting>
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[2017-08-24 23:32:01] [INFO] node "node2" (node ID: 2) monitoring upstream node "node1" (node ID: 1) in normal state
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[2017-08-24 23:32:08] [WARNING] unable to connect to upstream node "node1" (node ID: 1)
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[2017-08-24 23:32:08] [INFO] checking state of node 1, 1 of 5 attempts
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[2017-08-24 23:32:08] [INFO] sleeping 1 seconds until next reconnection attempt
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[2017-08-24 23:32:09] [INFO] checking state of node 1, 2 of 5 attempts
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[2017-08-24 23:32:09] [INFO] sleeping 1 seconds until next reconnection attempt
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[2017-08-24 23:32:10] [INFO] checking state of node 1, 3 of 5 attempts
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[2017-08-24 23:32:10] [INFO] sleeping 1 seconds until next reconnection attempt
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[2017-08-24 23:32:11] [INFO] checking state of node 1, 4 of 5 attempts
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[2017-08-24 23:32:11] [INFO] sleeping 1 seconds until next reconnection attempt
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[2017-08-24 23:32:12] [INFO] checking state of node 1, 5 of 5 attempts
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[2017-08-24 23:32:12] [WARNING] unable to reconnect to node 1 after 5 attempts
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INFO: setting voting term to 1
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INFO: node 2 is candidate
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INFO: node 3 has received request from node 2 for electoral term 1 (our term: 0)
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[2017-08-24 23:32:12] [NOTICE] this node is the winner, will now promote self and inform other nodes
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INFO: connecting to standby database
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NOTICE: promoting standby
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DETAIL: promoting server using '/home/barwick/devel/builds/HEAD/bin/pg_ctl -l /tmp/postgres.5602.log -w -D '/tmp/repmgr-test/node_2/data' promote'
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INFO: reconnecting to promoted server
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NOTICE: STANDBY PROMOTE successful
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DETAIL: node 2 was successfully promoted to primary
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INFO: node 3 received notification to follow node 2
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[2017-08-24 23:32:13] [INFO] switching to primary monitoring mode</programlisting>
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</para>
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<para>
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The cluster status will now look like this, with the original primary (<literal>node1</literal>)
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marked as inactive, and standby <literal>node3</literal> now following the new primary
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(<literal>node2</literal>):
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<programlisting>
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$ repmgr -f /etc/repmgr.conf cluster show
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ID | Name | Role | Status | Upstream | Location | Connection string
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----+-------+---------+-----------+----------+----------+----------------------------------------------------
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1 | node1 | primary | - failed | | default | host=node1 dbname=repmgr user=repmgr
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2 | node2 | primary | * running | | default | host=node2 dbname=repmgr user=repmgr
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3 | node3 | standby | running | node2 | default | host=node3 dbname=repmgr user=repmgr</programlisting>
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</para>
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<para>
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<command>repmgr cluster event</command> will display a summary of what happened to each server
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during the failover:
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<programlisting>
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$ repmgr -f /etc/repmgr.conf cluster event
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Node ID | Name | Event | OK | Timestamp | Details
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---------+-------+--------------------------+----+---------------------+-----------------------------------------------------------------------------------
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3 | node3 | repmgrd_failover_follow | t | 2017-08-24 23:32:16 | node 3 now following new upstream node 2
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3 | node3 | standby_follow | t | 2017-08-24 23:32:16 | node 3 is now attached to node 2
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2 | node2 | repmgrd_failover_promote | t | 2017-08-24 23:32:13 | node 2 promoted to primary; old primary 1 marked as failed
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2 | node2 | standby_promote | t | 2017-08-24 23:32:13 | node 2 was successfully promoted to primary</programlisting>
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</para>
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</chapter>
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