linux ha anno 2014

Linux HA anno 2014Julien PivottoJulien Pivotto

LOADays, AntwerpLOADays, AntwerpApril 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:IPaddr2params 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• Has a scoreHas a score

location prefer-apache-1 WebSite 50: apache-1ms 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• Has a scoreHas a score

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 resourcepcs resource create ClusterIP ocf:heartbeat:IPaddr2 \

ip=192.168.0.120 cidr_netmask=32 op monitor \interval=30s

Create constraintsCreate constraintspcs constraint colocation add WebFS WebDataClone\

INFINITY with-rsc-role=Master

pcs constraint order promote WebDataClone then \start WebFS

Standby a hostStandby a hostpcs cluster standby node1

Check the status of the clusterCheck the status of the clusterpcs status

Last updated: Fri Sep 14 12:41:12 2012Last change: Fri Sep 14 12:41:08 2012 via crm_attribute on pcmk-1Stack: corosyncCurrent DC: pcmk-1 (1) - partition with quorumVersion: 1.1.8-1.el7-60a19ed12fdb4d5c6a6b6767f52e5391e447fec02 Nodes configured, unknown expected votes5 Resources configured.

Node pcmk-1 (1): standbyOnline: [ pcmk-2 ]

Full list of resources:

ClusterIP (ocf::heartbeat:IPaddr2): Started pcmk-2WebSite (ocf::heartbeat:apache): Started pcmk-2Master/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 codeexec { ’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 codeinclude cmaninclude pacemakercman_cluster {

’mycluster’:ensure => ’present’,logging => ’to_logfile="off"’,require => Class[’cman’],

}cman_clusternode{

$clusternodes:ensure => ’present’,require => Cman_cluster[’mycluster’];

New puppet codeNew puppet codeclass {

’cman::service’:ensure => ’running’,enable => true,require => Cman_clusternode[$clusternodes],

class {’pacemaker::service’:

ensure => ’running’,enable => true,require => Class[’cman::service’],

New puppet codeNew puppet codeClass[’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’,

New puppet codeNew puppet codecs_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’],

}Julien Pivotto Linux HA

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 youAny question?Any question?

ContactContactJulien PivottoJulien Pivottojulien@inuits.eujulien@inuits.eu@roidelapluie@roidelapluie

INUITS bvbaINUITS bvbaBelgiumBelgium+32 473 441 636+32 473 441 636https://inuits.euhttps://inuits.eu

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