Linux HA anno 2014

Linux HA anno 2014
Julien PivottoJulien Pivotto
LOADays, AntwerpLOADays, Antwerp
April 4th, 2014April 4th, 2014

whoamiwhoami
• sysadmin @ inuitssysadmin @ inuits
• open-source defender for 7+ yearsopen-source defender for 7+ years
• devops believerdevops believer
• @roidelapluie on twitter/github@roidelapluie on twitter/github
Julien Pivotto Linux HA

IntroductionIntroduction

What is HAWhat is HA
• High AvailabilityHigh Availability
• One service fail ⇒ another takes over its jobOne service fail ⇒ another takes over its job
• Transparent for the end-userTransparent for the end-user

Where HA will NOT helpWhere HA will NOT help
• It is not about scalabilityIt is not about scalability
• It will not fix your applicationIt will not fix your application
• It will make your application stableIt will make your application stable
• It is not a one-size-fits-all solutionIt is not a one-size-fits-all solution
• It is not about performancesIt is not about performances
• It is not backupIt is not backup

Why caring about HA?Why caring about HA?
• Service goes down at 5pm on Friday?Service goes down at 5pm on Friday?
• Downtime makes users unhappyDowntime makes users unhappy
• Downtime costs moneyDowntime costs money

What will not workWhat will not work
• Virtualization will not make your app HAVirtualization will not make your app HA
• VM mirroring is not HAVM mirroring is not HA
• Live migrations are not HALive migrations are not HA
• Containers are not HAContainers are not HA
• Cloud lolCloud lol

HA is about servicesHA is about services

Start on a good basisStart on a good basis
• AutomationAutomation
• MonitoringMonitoring
• CI / CDCI / CD
• TestingTesting
• . . . Then, start working on HA. . . Then, start working on HA

Eliminate the SPOFEliminate the SPOF
• Single Point of FailuresSingle Point of Failures
• Hardware failsHardware fails
• Disks always failDisks always fail
• etc. . .etc. . .
• Replicate. . .Replicate. . .

Split-BrainSplit-Brain
• Nodes can’t talk to each otherNodes can’t talk to each other
• They think they are aloneThey think they are alone
• They take decision and leadershipThey take decision and leadership
• Data inconsistencyData inconsistency

FencingFencing
• Shoot the other node in the headShoot the other node in the head
• Be sure a node is deadBe sure a node is dead
• Preserve integrity of the dataPreserve integrity of the data
• Combine with quorumsCombine with quorums

MonitoringMonitoring
• Monitoring if PID is running is uselessMonitoring if PID is running is useless
• Result-based monitoringResult-based monitoring
• Extract data out of itExtract data out of it
• E.g try to insert in DBE.g try to insert in DB

Cluster?Cluster?
• Active/active: everything is activeActive/active: everything is active
• Active/passive: nodes in standbyActive/passive: nodes in standby
• N+1: One node waiting in standbyN+1: One node waiting in standby
• N+M: Nodes waiting in standbyN+M: Nodes waiting in standby
• Can mix them etc. . .Can mix them etc. . .

http://clusterlabs.org/wiki (GFDL 1.2 licence)

KISS KISS KISSKISS KISS KISS

Fix you appFix you app

The StateThe State
• Stateless applicationStateless application
• Everything in DBEverything in DB
• Avoid temp ﬁlesAvoid temp ﬁles
• Disaster recoveryDisaster recovery

The right toolsThe right tools
• Make relevant choices for you appMake relevant choices for you app
• Look for HA in databasesLook for HA in databases
• Look for HA in queuing systemsLook for HA in queuing systems
• Look for HA in ﬁlesystems?Look for HA in ﬁlesystems?
• Master/Master vs Master/slaveMaster/Master vs Master/slave

The configurationThe configuration
• Same config everywhereSame config everywhere
• Use puppet, chef, . . .Use puppet, chef, . . .
• Config in one placeConfig in one place
• KISSKISS

PacemakerPacemaker

PacemakerPacemaker
• It is the brainIt is the brain
• Decides what to do, whenDecides what to do, when
• Gets information from ressourcesGets information from ressources
• Depends on messaging and cluster managerDepends on messaging and cluster manager
• Does not require shared storageDoes not require shared storage

DecisionsDecisions
• A node fails, now whatA node fails, now what
• A service fails, now whatA service fails, now what
• Restart? Move?Restart? Move?
• Needs to be quick and without interventionNeeds to be quick and without intervention
• Scores, policiesScores, policies

CIBCIB
• Cluster Information BaseCluster Information Base
• XML shared accross the clusterXML shared accross the cluster
• Updated using "pcs"Updated using "pcs"
• Contains knowledge about the clusterContains knowledge about the cluster

PrimitivesPrimitives
• Service, Ip address, mountpoint,. . .Service, Ip address, mountpoint,. . .
• Base bricks of a clusterBase bricks of a cluster
• Get a lot of parametersGet a lot of parameters
primitive ClusterIP ocf:heartbeat:IPaddr2
params ip="192.168.122.101" cidr_netmask="32"
op monitor interval="30s"

Resource AgentResource Agent
• ScriptScript
• How to startHow to start
• How to stopHow to stop
• How to change state (promote, demote)How to change state (promote, demote)
• How to monitor (real monitoring)How to monitor (real monitoring)
• An init script but way beterAn init script but way beter

ClonesClones
• Same resource running on multiple hostsSame resource running on multiple hosts
• Deﬁne minimum and maximum of running primitivesDeﬁne minimum and maximum of running primitives
• Possible to run multiple on the same nodePossible to run multiple on the same node
clone WebIP ClusterIP
meta globally-unique="true" clone-max="2"
clone-node-max="2"

Master Slave (ms)Master Slave (ms)
• Set of primitives with roleSet of primitives with role
• Masters and slaves (e.g mysql, ldap)Masters and slaves (e.g mysql, ldap)
• Can promote slaves to masterCan promote slaves to master
• Can demote masters to slaveCan demote masters to slave
• Multiples slaves / mastersMultiples slaves / masters
ms WebDataClone WebData
meta master-max="2" master-node-max="1"
clone-max="2" clone-node-max="1"

GroupGroup
• Group of primitives of different kindGroup of primitives of different kind
• Implies colocationImplies colocation
• Starts in a fixed orderStarts in a fixed order
• Stops in the opposite orderStops in the opposite order

ColocationColocation
• ConstraintConstraint
• Must run on the same hostsMust run on the same hosts
• Has a scoreHas a score
• Order mattersOrder matters
• e.g vip with servicee.g vip with service
colocation website-with-ip inf: WebSite ClusterIPproperty

LocationLocation
• Set preferred locationSet preferred location
location prefer-apache-1 WebSite 50: apache-1
ms WebDataClone WebData
meta master-max="2" master-node-max="1"
clone-max="2" clone-node-max="1"

OrderOrder
• What starts after whatWhat starts after what
• Even across nodesEven across nodes
pcs order WebFS-after-WebData inf: WebDataClone:promote
WebFSClone:start

PropertiesProperties
• expected-quorums-votesexpected-quorums-votes
• stonith-enabledstonith-enabled
property $id="cib-bootstrap-options"
dc-version="1.1.5-bdde4d02445be1f3d72e6a203ba2f"
cluster-infrastructure="openais"
expected-quorum-votes="2"
stonith-enabled="true"
no-quorum-policy="ignore"

MaintenanceMaintenance
• Manually move resourcesManually move resources
• Set a DO-NOT-MANAGE ﬂagSet a DO-NOT-MANAGE ﬂag
• Do not forget to revertDo not forget to revert

CMAN and CorosyncCMAN and Corosync

CMANCMAN
• Manages membership and quorumManages membership and quorum
• Notiﬁes pacemaker when something changesNotiﬁes pacemaker when something changes
• Starts and manages corosyncStarts and manages corosync
• Needs a cluster.conf that contains all the nodesNeeds a cluster.conf that contains all the nodes
• Managed via ccsManaged via ccs
• Will propagate the changesWill propagate the changes

CorosyncCorosync
• Messaging layerMessaging layer
• Controlled via CMANControlled via CMAN
• Next version will take over CMANNext version will take over CMAN

EnvironmentEnvironment

DistributionsDistributions
• Developed mainly by RedHat and SuSeDeveloped mainly by RedHat and SuSe
• Used with Openstack tooUsed with Openstack too
• Getting into a unique stackGetting into a unique stack
• Available in * distrosAvailable in * distros

crmsh vs pcscrmsh vs pcs
• crmsh was more usedcrmsh was more used
• Disappeared in CentOS 6.4Disappeared in CentOS 6.4
• Getting used to pcsGetting used to pcs
• One goal: modify the CIBOne goal: modify the CIB
• pcs is young/not widely usedpcs is young/not widely used

A PCS primerA PCS primer

Create a resourceCreate a resource
pcs resource create ClusterIP ocf:heartbeat:IPaddr2
ip=192.168.0.120 cidr_netmask=32 op monitor
interval=30s

Create constraintsCreate constraints
pcs constraint colocation add WebFS WebDataClone
INFINITY with-rsc-role=Master
pcs constraint order promote WebDataClone then
start WebFS

Standby a hostStandby a host
pcs cluster standby node1

Check the status of the clusterCheck the status of the cluster
pcs status
Last updated: Fri Sep 14 12:41:12 2012
Last change: Fri Sep 14 12:41:08 2012 via crm_attribute on pcmk-1
Stack: corosync
Current DC: pcmk-1 (1) - partition with quorum
Version: 1.1.8-1.el7-60a19ed12fdb4d5c6a6b6767f52e5391e447fec0
2 Nodes configured, unknown expected votes
5 Resources configured.
Node pcmk-1 (1): standby
Online: [ pcmk-2 ]
Full list of resources:
ClusterIP (ocf::heartbeat:IPaddr2): Started pcmk-2
WebSite (ocf::heartbeat:apache): Started pcmk-2
Master/Slave Set: WebDataClone [WebData]
Masters: [ pcmk-2 ]
Stopped: [ WebData:1 ]
WebFS (ocf::heartbeat:Filesystem): Started pcmk-2

Percona Replication ManagerPercona Replication Manager

Percona Replication ManagerPercona Replication Manager
• MySQL replication with pacemakerMySQL replication with pacemaker
• Complete documentationComplete documentation
• Ressource agentsRessource agents
• Supports multi-slave setupsSupports multi-slave setups
• Good documentationGood documentation

Mysql Ressource AgentMysql Ressource Agent
• Keeps track of a score for each slaveKeeps track of a score for each slave
• In case of failure, will switch to the "best scored"In case of failure, will switch to the "best scored"
• Can be reused in your clusterCan be reused in your cluster
• https://github.com/percona/percona-pacemaker-agentshttps://github.com/percona/percona-pacemaker-agents

PuppetPuppet

puppetlabs-corosyncpuppetlabs-corosync
• "Reference" module"Reference" module
• Creates resources, constraints. . .Creates resources, constraints. . .
• crmsh providercrmsh provider
• https://github.com/clusterlabs/puppetlabs-corosynchttps://github.com/clusterlabs/puppetlabs-corosync
• https://github.com/roidelapluie/puppetlabs-corosync (pcs)https://github.com/roidelapluie/puppetlabs-corosync (pcs)

Old puppet codeOld puppet code
exec { ’loadcrmconfig’:
refreshonly => true,
command => ’/bin/sleep 5; /usr/sbin/crm
configure load replace
/etc/mediasalsa/cib.cfg >>/tmp/empty 2>&1’,
subscribe => File[’/etc/project/cib.cfg’],
}

New puppet codeNew puppet code
include cman
include pacemaker
cman_cluster {
’mycluster’:
ensure => ’present’,
logging => ’to_logfile="off"’,
require => Class[’cman’],
}
cman_clusternode{
$clusternodes:
ensure => ’present’,
require => Cman_cluster[’mycluster’];
}

class {
’cman::service’:
ensure => ’running’,
enable => true,
require => Cman_clusternode[$clusternodes],
}
class {
’pacemaker::service’:
ensure => ’running’,
enable => true,
require => Class[’cman::service’],
}

Class[’cman::service’, ’pacemaker::service’]->
Cs_property<||>->
Cs_primitive<||>
cs_property {
’stonith-enabled’:
ensure => present,
value => ’false’,
}
cs_property {
’no-quorum-policy’:
ensure => present,
value => ’ignore’,
}

cs_primitive { "mysql-${name}":
provider => ’pcs’,
primitive_class => ’ocf’,
primitive_type => ’mysql’,
provided_by => ’inuits’,
parameters => {
’test_user’ => $test_user,
’test_passwd’ => $test_passwd,
’test_table’ => $test_table,
},
operations => {
’monitor’ => {
’interval’ => ’10s’,
},
},
require => Cs_property[’stonith-enabled’],
}

ConclusionsConclusions

Be cleverBe clever
• KISSKISS
• AutomateAutomate
• MonitorMonitor
• Be realisticBe realistic

Do not promise the impossibleDo not promise the impossible
• WONTFIX your appWONTFIX your app
• Working together (devops)Working together (devops)
• Not about scaleNot about scale
• Not about stabilityNot about stability
• Do not talk in ninesDo not talk in nines

Linux HALinux HA
• ReliableReliable
• Pacemaker, Corosync, CMANPacemaker, Corosync, CMAN
• Pcs, crmsh, ccsPcs, crmsh, ccs
• A lot of readingA lot of reading
• A lot of experience to buildA lot of experience to build

RTFMRTFM
• http://clusterlabs.orghttp://clusterlabs.org
• Clusters From ScratchClusters From Scratch
• Pacemaker explainedPacemaker explained
• http://blog.clusterlabs.orghttp://blog.clusterlabs.org
• Old http://linux-ha.orgOld http://linux-ha.org

Thank youThank you
Any question?Any question?

ContactContact
Julien PivottoJulien Pivotto
julien@inuits.eujulien@inuits.eu
@roidelapluie@roidelapluie
INUITS bvbaINUITS bvba
BelgiumBelgium
+32 473 441 636+32 473 441 636
https://inuits.euhttps://inuits.eu

Linux HA anno 2014

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