galera cluster across multiple dc's

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john test

• September 08, 2015 16:54

Hi there,

We are implementing a cross-site Galera cluster.

I am a bit confused from docs regarding the number of nodes: does the total nodes need to be an odd number or nodes per site need to be odd?

We want to have 2 nodes per site, but will add a garb node to make it odd to avoid split scenario if needed.

 

Thank you!

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  Ashraf Sharif

  • September 09, 2015 00:42

  Hi,

  Total nodes (across sites) need to be an odd number. Let's say if you have A,B,C as the sites. If you have 2 sites, A holds primary status where garbd is located and B holds the secondary. Both sites are master and sync up until site A goes down. If site A is down, site B won't work unless you rebootstrap the cluster on B. 

  If you have 3 sites, place the garbd in C so A and B are master and hold the primary status. If any of A or B goes down, either site can still serve as a master since site C is there as the arbitrator. 

  Take a look at this blog post for more examples:

  http://severalnines.com/blog/architecting-failure-disaster-recovery-mysqlmariadb-galera-cluster

  Regards,

  Ashraf

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  john test

  • September 09, 2015 00:54

  Thanks Ashraf.

  So is it preferable to have garbd node in 3rd site or is it fine if we have it in site A or B in case of 2-site solution?

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  Ashraf Sharif

  • September 09, 2015 02:01

  For more resilient solution, garbd on third site is preferable but it could cost you more. If you have very good connectivity between both sites, 2-site solution would be enough though. It's your call really. Either one has its own advantages.

   

  Regards,

  Ashraf

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  john test

  • September 09, 2015 13:18

  Thank you.

  In fact, the connectivity is not very good between the 2 sites. This is the reason we were initially considering 2 separate galera clusters with mysql multi-master replication between them. but we ran into other issues with this glue approach so we chose just deploy one galera cluster across the 2 sites.

  What would you recommend as the best solution?

   

  Thank you for your help!

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