High Availability with MariaDB Enterprise - Roadshow Helsinki 2014

© SkySQL Corpora-on Ab. Company Confiden-al. 24/06/2014 1

© SkySQL Corpora-on Ab. Company Confiden-al.

High Availability with MariaDB Enterprise

Anders Karlsson Sales Engineer, SkySQL

* * 24/06/2014 2


Agenda

• Introduc-on to High Availability • Different services that need HA • Different components of High Availability • Different MariaDB HA Solu-ons

•  HA using MariaDB Replica-on •  HA using MariaDB Galera Cluster

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Introduc-on to High Availability

High availability is a system design protocol and associated

implementation that ensures a certain degree of operational continuity during

a given measurement period

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• High Availability isn’t always the same as Long Up(me

•  A system that is “up” might s-ll not be accessible •  A system that is “down” just once, but for a long -me, isn’t highly available

• High Availability rather means •  Long Mean Time Between Failures (MTBF) •  Short Mean Time To Recover (MTTR)



• The level of availability is measured as the ra-o of -me the system is available over a year, expressed as a percentage

•  99.9% availability means that the system is available at least 8.751 of 8.760 hours in a year, or that it is unavailable at the most 9 hours per year •  99.999% availability means that the system is available at least 525.595 or 525.600 minutes in a year, or that it is unavailable at the most 5 minutes per year

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Maintaining High Availability

• There are two common situa-ons that we try to protect ourselves from using an HA solu-on

•  Datacenter failure – A whole datacenter becomes unavailable for some reason, like power failure, network failure, a virus or similar situa-ons •  Server failure – An individual server fails because of a hardware failure or something similar

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Services in an HA Solu-on

• All services that make up the applica-on stack needs HA for the system to achieve HA

•  Web servers •  Applica-on servers •  Applica-ons •  Database servers •  Storage •  Network

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Services in an HA Solu-on

• Of the different types of services, there are two types

•  Stateless services These servers has no state beyond the current opera-on. If such a server fails, another server of the same type can replace it without having to transfer any set of data. Webservers and applica-on servers are typical stateless services

•  Stateful services These services maintains a state, and that state needs to be preserved if a server fails, and has to be made available to any other server that takes it place. A database service such as a MariaDB server is a typical stateful service

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Components of High Availability

• Monitoring and Management •  Availability of the services needs to be monitored, to be able to take ac-on when there is a failure. A failover can be manual or automa-c, but it has to be managed

• Failover / Load Balancing mechanism •  Some mechanism to redirect traffic from the failed server or Datacenter and to a working one

• Data redundancy •  For stateful services, we need to make sure that data is somehow made redundant

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Monitoring and Management

• There are many different solu-ons here, some focused on specific services (in par-cular database), some as part of a Load Balancing soeware solu-on of an Appliance or a pure soeware based solu-on such as LinuxHA

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Failover mechanism

• There is a wide range of op-ons here too, in par-cular when it comes to Datacenter failover, which can be more complicated

• Common mechanisms range from applica-on based failover and DNS failover to Load Balancing and Network Failover

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Data Redundancy

• Providing Data Redundancy is complex, error prone and takes a toll on performance

• It also has to be men-oned that a SAN does not provide redundancy just because a disk set can be failed over from one server to another. A SAN might be a SPOF, but in some cases that is a risk that some customers is willing to take

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Data Redundancy with MariaDB

• For MariaDB, there are a number of op-ons for Data Redundancy

•  MariaDB Classic Replica-on •  MariaDB Galera Cluster •  Storage based redundancy (Ac-ve / Passive setups)

•  DRBD (Distributed Replicated Block Device) •  SAN (Storage Area Network)

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HA using MariaDB Replica-on

• This is in many cases a good enough solu-on, but it has some issues

•  The cluster is very loosely coupled, not all nodes are aware of all the other nodes for example •  Replica-on is asynchronous, so failing over is more difficult than usually (but MHA solves this) •  Adding a slave is difficult

• But there are also many advantages •  Low performance penalty •  Well known and easy to use technology

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HA using MariaDB Galera Cluster

• This a soeware-‐only solu-on with many advantages

•  Scales writes and well as reads •  “Proper” Cluster with built-‐in failover, locking and split-‐brain protec-on •  Synchronous replica(on with low overhead due to op-mis-c locking

• There are some disadvantages •  More overhead than using Asynchronous Replica-on •  Only works with InnoDB •  For distributed writes, some restric-ons apply

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MariaDB Galera Cluster setup

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MariaDB Server MariaDB Server MariaDB Server

Galera wsrep Library Galera wsrep Library Galera wsrep Library

Synchronous Replication

Load Balancer / Failover

Application / Application server


Sehng up MariaDB Galera Cluster

• MariaDB Galera Cluster consists of the MariaDB binary that in turns talks to the Galera wsrep library

• Once set up, Galera is configured using the usual my.cnf file, and is monitored using the SHOW GLOBAL STATUS command

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MariaDB Galera Cluster failover

• MariaDB Galera Cluster handles failed servers internally

• MariaDB Galera Cluster also handles split-‐brain protec(on and this requires at least 3 servers

• MariaDB Galera Cluster can also be configured without split-‐brain protec-on, for example when failover is manual or is handled in some other way

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MariaDB Galera Cluster setup

• If necessary to allow for protec-on against split-‐brain scenarios, but only using 2 database servers, a third server can be set up with a Galera specific arbitra(on agent

• Galera also can be used with it’s own simple Load Balancer, although it is much more common that other technologies are used, such as HA aware Connectors or a Load Balancer

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Ques(ons?

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High Availability with MariaDB Enterprise - Roadshow Helsinki 2014

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