1. WHO WANTS A SERVICE
WITH ZERO DOWNTIME?

2. … EVERYBODY

3. IS IT THAT GOOD?

4. NOT JUST TECHNOLOGY.
RISKS, PROCEDURES, PEOPLE

5. FROM 0 TO ~100:
BUSINESS
CONTINUITY WITH
POSTGRESQL
Gabriele Bartolini
Head of Support @ 2ndQuadrant
PgDay.IT 2017, Milan

6. 2ndquadrant.com
@_GBartolini_ #PGDayIT
ABOUT MYSELF
▸ Open Source passionate and programmer since 1995
▸ First time with Postgres in 1997, regular from ~2000
▸ Lean and DevOps practitioner
▸ Co-Founder of ITPUG and PostgreSQL Europe
▸ Entrepreneur, with 2ndQuadrant since 2008
▸ Co-Author of “PostgreSQL Administration Cookbook”
▸ Came up with the name “Barman”

7. 2ndquadrant.com
@_GBartolini_ #PGDayIT
BUSINESS CONTINUITY
▸ Disaster Recovery
▸ High Availability
▸ Types of disaster/failures
▸ Availability = Uptime / (Uptime + Downtime)

8. 2ndquadrant.com
@_GBartolini_ #PGDayIT
OBJECTIVES
▸ Recovery Point Objective (RPO)
▸ How much data can I afford to lose?
▸ Recovery Time Objective (RTO)
▸ How long will it take me to recover?

9. 2ndquadrant.com
@_GBartolini_ #PGDayIT
SERVICE RELIABILITY
▸ Cost of downtime
▸ How many €/$/£/AUD/…?
▸ Risk management
▸ SLI, SLO and SLA

10. 2ndquadrant.com
@_GBartolini_ #PGDayIT
SOME NOTES FOR THIS PRESENTATION
▸ PostgreSQL on Linux
▸ Servers can be either physical or virtual
▸ Storage must be redundant
▸ RAID is required
▸ VOLUME: redundant disk mounted on a system

11. LET’S START

12. 0.
ONE POSTGRES SERVER

13. 2ndquadrant.com
@_GBartolini_ #PGDayIT
ARCHITECTURE
Server name: hope

14. 2ndquadrant.com
@_GBartolini_ #PGDayIT
RECAP
▸ Why is RPO = ∞?
▸ Why is RTO = n/a?
▸ “Hope is not a strategy” (cit. Google)
▸ More common than you’d expect

15. 10.
ONE POSTGRES SERVER
+ LOGICAL BACKUPS

16. 2ndquadrant.com
@_GBartolini_ #PGDayIT
ARCHITECTURE
Add systematic backups
with pg_dump
LOGICAL
BACKUP LOGICAL
BACKUP
LOGICAL
BACKUP
…
Day 0
4AM
Day -1
4AM
Day -2
4AM

17. 2ndquadrant.com
@_GBartolini_ #PGDayIT
RECAP
▸ How do you feel now?
▸ Still: RPO = ∞ and RTO = n/a. Why?
▸ A backup is valid only if you have tested it
▸ Unfortunately, this is very common

18. 20.
ONE POSTGRES SERVER
+ LOGICAL BACKUPS
+ LOGICAL RESTORES

19. 2ndquadrant.com
@_GBartolini_ #PGDayIT
ARCHITECTURE
Test your backups
with pg_restore
LOGICAL
BACKUP
Day 0
4AM

20. 2ndquadrant.com
@_GBartolini_ #PGDayIT
DEFINING SOME OBJECTIVES
▸ Measure time for pg_restore
▸ RPO = backup frequency
▸ RTO = maximum time of recovery
▸ Provision another server
▸ Configure another server (automated, right?)
▸ Time to restore the last backup (measure it)

21. HAVE WE REALLY THOUGHT
ABOUT EVERYTHING?

22. TIME OF REACTION

23. 2ndquadrant.com
@_GBartolini_ #PGDayIT
RECAP
▸ Can this architecture work for you?
▸ We need reliable monitoring
▸ From now on, we assume we have it in place!
▸ We need to reduce both RPO and RTO

24. HOW?
POINT-IN-TIME-RECOVERY

26. 2ndquadrant.com
@_GBartolini_ #PGDayIT
POSTGRESQL’S PITR
▸ Part of core (fully open source)
▸ Rebuild a cluster at a point in time
▸ From crash recovery to sync streamrep (physical/logical)
▸ RPO = 0 (zero data loss)
▸ Hot base backup, continuous WAL archiving, Recovery
▸ API

27. 2ndquadrant.com
@_GBartolini_ #PGDayIT
BASIC CONCEPTS
▸ Continuous copy of WAL data (continuous archiving)
▸ Physical base backups
▸ Recovery:
▸ copy base backup to another location
▸ recovery mode (replay of WALs until target)

28. 2ndquadrant.com
@_GBartolini_ #PGDayIT
BARMAN
▸ In this presentation: Barman 2.3
▸ Open Source (GNU GPL 3)
▸ Written in Python
▸ Developed and maintained by 2ndQuadrant
▸ Available at www.pgbarman.org

29. 40.
ONE POSTGRES SERVER
+ ONE BARMAN SERVER

30. 2ndquadrant.com
@_GBartolini_ #PGDayIT
ARCHITECTURE
Continuous backup

31. 2ndquadrant.com
@_GBartolini_ #PGDayIT
BASIC CONCEPTS
▸ Remote backup and recovery
▸ Multiple server management
▸ Backup catalogue and WAL archive
▸ Retention policies

32. 2ndquadrant.com
@_GBartolini_ #PGDayIT
COPY METHOD
▸ PostgreSQL streaming
▸ Practical/Windows/Docker
▸ Rsync/SSH
▸ Incremental backup and recovery (via hard links)
▸ Parallel backup and recovery
▸ Network compression and bandwidth limitation

33. 2ndquadrant.com
@_GBartolini_ #PGDayIT
WAL SHIPPING METHOD
▸ “archiving”, through “archive_command”:
▸ RPO ~ 16MB of WAL data, or
▸ “archive_timeout”
▸ “streaming”, through streaming replication:
▸ “pg_receivewal” or “pg_receivexlog”
▸ continuous stream, RPO ~ 0
▸ PostgreSQL 9.2+ required

34. 2ndquadrant.com
@_GBartolini_ #PGDayIT
EXAMPLE FROM POSTGRESQL.CONF
archive_mode = on
wal_level = logical
max_wal_senders = 10
max_replication_slots = 10
archive_command = 'rsync -a %p
barman@HOST:/var/lib/barman/ID/incoming'

35. 2ndquadrant.com
@_GBartolini_ #PGDayIT
EXAMPLE FROM BARMAN.CONF
[angus]
description = “Angus Young database"
ssh_command = ssh postgres@angus
conninfo = user=barman-acdc dbname=postgres host=angus
retention_policy = RECOVERY WINDOW OF 6 MONTHS
copy_method = rsync
reuse_backup = link
parallel_jobs = 4
archiver = true
streaming_archiver = true
slot_name = barman_streaming_acdc

36. 2ndquadrant.com
@_GBartolini_ #PGDayIT
RECAP
▸ How do you feel now?
▸ Still: RPO = ∞ and RTO = n/a. Why?
▸ A backup is valid only if you have tested it
▸ Barman reduces backup risks, does not exclude them
▸ Systematic tests (especially custom scripts)
▸ Business risk is very high

37. 60.
ONE POSTGRES SERVER
+ ONE BARMAN SERVER
+ ONE RECOVERY SERVER

38. 2ndquadrant.com
@_GBartolini_ #PGDayIT
ARCHITECTURE
Test your backups
with barman recover

39. WHAT A WASTE!

40. TESTING OR BI?
HAVE YOU EVER THOUGHT OF USING IT FOR

41. 2ndquadrant.com
@_GBartolini_ #PGDayIT
HOOK SCRIPTS
▸ Barman has hook scripts:
▸ pre and post backup
▸ pre and post archiving
▸ with retry option (until the script returns SUCCESS)

42. 2ndquadrant.com
@_GBartolini_ #PGDayIT
EXAMPLE OF RECOVERY SCRIPT
▸ Write a bash script that:
▸ connects to a remote server via SSH
▸ stops the PostgreSQL server
▸ issues a “barman recover” with target “immediate”
▸ starts the PostgreSQL
▸ Set it as post-backup script

43. 2ndquadrant.com
@_GBartolini_ #PGDayIT
SOME FOOD FOR THOUGHT
▸ Outcomes:
▸ Systematically test your backup
▸ Measure your recovery time
▸ Identical server? This is a backup server ready to start
▸ You can use a different data centre
▸ Be creative, PostgreSQL gives you infinite freedom!

44. 2ndquadrant.com
@_GBartolini_ #PGDayIT
RECAP
▸ RPO ~ 0 (your backups work, every time)
▸ RTO = Time of reaction + Recovery time
▸ Example: RPO ~0 and RTO < 1 day
▸ Acceptable or not acceptable?
▸ Entry level architecture for business continuity
▸ Priority now: improve RTO

45. HOW?
REPLICATION

46. 2ndquadrant.com
@_GBartolini_ #PGDayIT
POSTGRESQL’S REPLICATION
▸ Part of core (fully open source)
▸ One master, multiple standby servers
▸ Evolution of PITR
▸ Standby server is in continuous recovery mode
▸ Hot standby (read-only)
▸ Both streaming (9.0+) and file based pulling of WAL
▸ Cascading from a standby

47. 2ndquadrant.com
@_GBartolini_ #PGDayIT
SYNCHRONOUS REPLICATION
▸ Fine control (from global down to transaction level)
▸ 2-safe replication
▸ COMMIT of a write transactions waits until written on
both the master and a standby (or more from 9.6)
▸ More than a synchronous client is required
▸ Read consistency of a cluster
▸ RPO = 0 (zero data loss)

48. 80.
TWO POSTGRES SERVERS
+ ONE BARMAN SERVER
+ ONE RECOVERY SERVER

49. 2ndquadrant.com
@_GBartolini_ #PGDayIT
ARCHITECTURE
barman_restore_wal
barman recover
Symmetric Cluster
master standbyANGUS MALCOLM

50. 2ndquadrant.com
@_GBartolini_ #PGDayIT
EXCERPT FROM POSTGRESQL’S CONFIGURATION
postgresql.conf:
hot_standby = on
recovery.conf:
standby_mode = ‘on'
# Streaming
primary_conninfo = 'host=angus user=replica application_name=ha
sslmode=require’
# Fallback via Barman
restore_command = 'barman-wal-restore -U barman acdc angus %f %p'

51. 2ndquadrant.com
@_GBartolini_ #PGDayIT
SWITCHOVER (PLANNED)
▸ Applications are paused (start of downtime)
▸ Shut down the master
▸ Allow the standby to catch up with the master
▸ Promote the standby
▸ Switch virtual IPs
▸ Resume applications (end of downtime)
▸ Reconfigure the former master as standby

52. 2ndquadrant.com
@_GBartolini_ #PGDayIT
FAILOVER (UNPLANNED)
▸ The master is down (start of downtime)
▸ Promote the standby
▸ Change the virtual IP
▸ DEGRADED SYSTEM

53. 2ndquadrant.com
@_GBartolini_ #PGDayIT
MANUAL SWITCHOVER AND FAILOVER
▸ Manual switchover != manual switchover procedure
▸ Manual switchover = manually triggered
▸ Automate the procedure!!!
▸ bash (good)
▸ Ansible (better)
▸ Enhance gradually

54. 2ndquadrant.com
@_GBartolini_ #PGDayIT
RECAP
▸ RPO ~ 0 (your backups work, every time)
▸ RTO = Time of reaction + Time of promotion
▸ Criticality: manual intervention
▸ Reliable monitoring
▸ Trained people (practice & docs!)

55. 2ndquadrant.com
@_GBartolini_ #PGDayIT
MANUAL FAILOVER VS AUTOMATED FAILOVER
▸ Risk management
▸ Split brain nightmare
▸ Automated is built on manual (test!)
▸ Your choice
▸ Very good solution for business continuity
▸ Uptime > 99.99% in a year

56. 90.
TWO POSTGRES SYNC SERVERS
+ ONE BARMAN SERVER
+ ONE RECOVERY SERVER

57. 2ndquadrant.com
@_GBartolini_ #PGDayIT
ARCHITECTURE
barman_restore_wal
barman recover
Potential synchronous
Synchronous
ZERO DATA LOSS

58. 2ndquadrant.com
@_GBartolini_ #PGDayIT
SYNCHRONOUS REPLICATION
▸ Primary: Barman
▸ Zero data loss backup
▸ Primary: Standby
▸ Zero data loss cluster (reduce RTO)
▸ Just one configuration line in PostgreSQL
▸ synchronous_standby_names = '1 (ha, barman_receive_wal)'

59. ~100.
TWO POSTGRES SYNC SERVERS
+ ONE BARMAN SERVER
+ ONE RECOVERY SERVER
+ REPMGR (AUTO-FAILOVER)

60. 2ndquadrant.com
@_GBartolini_ #PGDayIT
ARCHITECTURE
Potential synchronous
Synchronous
repmgr repmgr
repmgr witness

61. WHAT’S MORE?

62. 2ndquadrant.com
@_GBartolini_ #PGDayIT
PUSH THE BOUNDARIES
▸ Repeatable architectures
▸ PgBouncer
▸ Virtual IPs
▸ S3 relay via Barman hook scripts
▸ Multiple standby servers and cascading replication
▸ Docker containers
▸ Logical replication backups

63. 2ndquadrant.com
@_GBartolini_ #PGDayIT
CONCLUSIONS
▸ Babysteps and KISS
▸ New? Explore and learn
▸ Practice is the only way to mastery (drills)
▸ Plan regular healthy downtimes
▸ Use switchovers to perform PostgreSQL updates
▸ Smart downtimes increase long-term uptime

64. 2ndquadrant.com
@_GBartolini_ #PGDayIT
ANY QUESTIONS?
▸ PostgreSQL: www.postgresql.org
▸ Barman: www.pgbarman.org
▸ Barman Cli: github.com/2ndquadrant-it/barman-cli
▸ PgBouncer: pgbouncer.github.io
▸ Repmgr: www.repmgr.org
▸ Our blog: blog.2ndquadrant.com

65. 2ndquadrant.com
@_GBartolini_ #PGDayIT
LICENCE
Attribution 4.0 International (CC BY 4.0)
You are free to:
▸ Share — copy and redistribute the material in any medium or
format
▸ Adapt — remix, transform, and build upon the material for any
purpose, even commercially.
The licensor cannot revoke these freedoms as long as you follow
the license terms.