1. Swapping
Pacemaker/Corosync for
repmgr
pgDay Asia 2016
Ang Wei Shan
17th March 2016 Disclaimer: I don’t work for 2ndQuadrant

2. Agenda
● Introduction
● Challenges with Pacemaker/Corosync
● Pg_bouncer
● Linux’s UCARP
● 2ndQuadrant’s repmgr
● Demo

3. Agenda
● Introduction
● Challenges with Pacemaker/Corosync
● Pg_bouncer
● Linux’s UCARP
● 2ndQuadrant’s repmgr
● Demo

4. ● Database Administrator
● > 4 years of experience in databases
● Worked with majority of the RDBMS
● ≈ 350 days with PostgreSQL

5. Agenda
● Introduction
● Challenges with Pacemaker/Corosync
● Pg_bouncer
● Linux’s UCARP
● 2ndQuadrant’s repmgr
● Demo

6. ● Open-source alternative to Red Hat Cluster Suite
● Extremely popular choice in the open-source world
● Made up of 2 different stack of software
○ Pacemaker
○ Corosync/Heartbeat
● Complicated to get the configuration correct

7. Online: [ node1 node2 ]
Full list of resources:
stonith_node1 (stonith:fence_ipmilan): Stopped
stonith_node2 (stonith:fence_ipmilan): Stopped
vip-slave (ocf::heartbeat:IPaddr2): Started node1
Master/Slave Set: msPostgresql [pgsql]
Masters: [ node1 ]
Stopped: [ pgsql:1 ]
Resource Group: master-group
vip-master (ocf::heartbeat:IPaddr2): Started node1
vip-rep (ocf::heartbeat:IPaddr2): Started node1
Node Attributes:
* Node node1:
+ master-pgsql : 1000
+ pgsql-data-status : LATEST
+ pgsql-master-baseline : 00000070C6FCF9F0
+ pgsql-status : PRI
* Node node2:
+ master-pgsql : -INFINITY
+ pgsql-data-status : DISCONNECT
+ pgsql-status : STOP
Migration summary:
* Node node2:
stonith_node1: migration-threshold=1000000 fail-count=1000000 last-failure='Thu Feb 4 13:43:49 2016'
pgsql:0: migration-threshold=1 last-failure='Thu Feb 4 13:46:14 2016'
* Node node1:
stonith_node2: migration-threshold=1000000 fail-count=1000000 last-failure='Thu Feb 4 13:38:45 2016'
pgsql_start_0 (node=node2, call=84, rc=1, status=complete): unknown error

8. Feb 4 17:08:12 node1 attrd[3149]: notice: attrd_perform_update: Sent delete 46: node=node1, attr=last-f
ailure-stonith_node2, id=<n/a>, set=(null), section=status
Feb 4 17:08:12 node1 stonith-ng[3147]: notice: stonith_device_register: Device 'stonith_node2' already existed in device
list (2 active devices)
Feb 4 17:08:14 node1 stonith-ng[3147]: notice: log_operation: Operation 'monitor' [8201] for device 'stonith_node2' retur
ned: -1001 (Generic Pacemaker error)
Feb 4 17:08:14 node1 stonith-ng[3147]: warning: log_operation: stonith_node2:8201 [ ERROR: Failed to authenticate to https
://cathy.rocketwork.com.sg:4000 as node1 with key /etc/chef/client.pem ]
Feb 4 17:08:14 node1 stonith-ng[3147]: warning: log_operation: stonith_node2:8201 [ Getting status of IPMI:10.51.113.22...
Spawning: '/usr/bin/ipmitool -I lanplus -H '10.51.113.22' -U 'pacemaker' -L 'OPERATOR' -P '' -v chassis power status'... ]
Feb 4 17:08:14 node1 stonith-ng[3147]: warning: log_operation: stonith_node2:8201 [ Failed ]
Feb 4 17:08:15 node1 crmd[3151]: error: process_lrm_event: LRM operation stonith_node2_start_0 (call=52, status=4, cib-u
pdate=48, confirmed=true) Error
Feb 4 17:08:15 node1 crmd[3151]: warning: status_from_rc: Action 5 (stonith_node2_start_0) on node1 fai
led (target: 0 vs. rc: 1): Error
Feb 4 17:08:15 node1 crmd[3151]: warning: update_failcount: Updating failcount for stonith_node2 on node1
after failed start: rc=1 (update=INFINITY, time=1454576895)
Feb 4 17:08:15 node1 attrd[3149]: notice: attrd_trigger_update: Sending flush op to all hosts for: fail-count-stonith_dain
a2 (INFINITY)
Feb 4 17:08:15 node1 crmd[3151]: warning: update_failcount: Updating failcount for stonith_node2 on node1
after failed start: rc=1 (update=INFINITY, time=1454576895)
Feb 4 17:08:15 node1 crmd[3151]: notice: run_graph: Transition 12 (Complete=2, Pending=0, Fired=0, Skipped=1, Incomplete=0
, Source=unknown): Stopped
Feb 4 17:08:15 node1 attrd[3149]: notice: attrd_perform_update: Sent update 51: fail-count-stonith_node2=INFINITY
Feb 4 17:08:15 node1 attrd[3149]: notice: attrd_trigger_update: Sending flush op to all hosts for: last-failure-stonith_da

9. Agenda
● Introduction
● Challenges with Pacemaker/Corosync
● Pg_bouncer
● Linux’s UCARP
● 2ndQuadrant’s repmgr
● Demo

10. ● Lightweight connection pooler for PostgreSQL
● Open-source
● Acts as the single point of entry to the database
● Useful for managing huge number of incoming
connections to the database
● Latest version - v1.7.2

11. Agenda
● Introduction
● Challenges with Pacemaker/Corosync
● Pg_bouncer
● Linux’s UCARP
● 2ndQuadrant’s repmgr
● Demo

12. ● Common Address Redundancy Protocol (CARP)
● Linux’s implementation of CARP from FreeBSD
● Allows multiple hosts to share a single IP address
● Management of Virtual IP for failover purpose
● For client connectivity to Pg_bouncer
● Latest version => v1.5.2

13. Agenda
● Introduction
● Challenges with Pacemaker/Corosync
● Pg_bouncer
● Linux’s UCARP
● 2ndQuadrant’s repmgr
● Demo

14. ● Developed by 2ndQuadrant
● Open-source
● Manages replication and failover for your
PostgreSQL HA cluster
● Latest version - v3.1.1

15. ● Linux or Unix only
● repmgr 2.0 is for PostgreSQL 9.0 to 9.4
● repmgr 3.0 is for PostgreSQL 9.3 or higher
● Does not take care of client failover!!

16. ● Automatic failover capabilities
● Provisioning of standby servers
● 2 main tools
○ repmgr => Perform administrative tasks
○ repmgrd => Perform monitoring, automatic failover and
notification events

17. ● Requires a database to store cluster metadata
● Runs as postgres user
● Password-less SSH connectivity between all
hosts
● Recommended to run at with an odd number
cluster

18. The decision whether a server can be promoted depends whether the majority of servers are
"visible". If you have three servers - primary and standby in one location, and a second
standby in another location - and the network to the second standby goes down, the second
standby will see it's in the minority (its location represents 1/3 of the servers) and won't
promote itself.
If you have two servers in each location, you'd need an additional witness server so one
location still has a "majority" - otherwise in the event of a network disconnection you might
end up with one standby in each location promoting itself.

19. Agenda
● Introduction
● Challenges with Pacemaker/Corosync
● Pg_bouncer
● Linux’s UCARP
● 2ndQuadrant’s repmgr
● Demo

20. Thank you for your attention!
weishan.ang@gmail.com
newbiedba.wordpress.com
sg.linkedin.com/in/weishan