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I'm wondering how to handle multiple datacenters for CD servers in Azure PaaS.

According to this ( https://kb.sitecore.net/articles/610106 ) you can use transactional replication for your Web databases (even though it's not really necessary, and has some limitations/caveats), but what to do about the Core databases? I can't seem to find any official information about how to handle those using Azure SQL Databases.

I'm asking this question related to Sitecore 8.2 update 2 with official Azure PaaS support.

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As you mentioned Replication is required for some Sitecore databases, but SQL Azure (PaaS) does not support SQL read-write geo-replication currently just read-only(https://docs.microsoft.com/en-us/azure/sql-database/sql-database-designing-cloud-solutions-for-disaster-recovery), so the only option is to have all CD locations connect to the central Core database. On the other hand Web databases could be set up in different locations for every CD using publishing targets.

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If you are trying to go active active.

I'd look at using the new publishing service in the context of Azure SQL (PAAS) to get the web database changes published out to different regions. (as Azure SQL Geo-Replication is read only in the replicas, and sitecore requires write access to update the properties table)

For the Core database though no equivalent of the new publishing service AFAIK. Depending what you need out of the Core database, you may be able to get away with having a Core database in each region not kept in sync. (and manually update/keep in sync changes as required) There is a scaling guide with 3 scenarios I recall, where outside of PAAS you could setup replication (I recall some modifications required to Core databases to support this), which won't work in PAAS. Or replay security events.
Main issues are keeping security tables in sync. If your content authors are only in one region, and you don't rely on that for authentication on content delivery, may not need it to be kept in sync. Other usages of core database are links database. Storing which is the active solr collection for each index. Would be good to have a definitive list.

For DR scenario you could have a Geo Replicated core database, and fail over that when you want to fail over content authoring.

Hope that helps.

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    Thank you for the information and the options, but we would like to keep an officially supported setup for this project. – Xuntar Apr 11 '17 at 8:30
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    This is supported see sdn.sitecore.net/upload/sitecore7/70/scaling_guide_sc70_a4.pdf – Ian Apr 11 '17 at 12:16
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    See section "Addressing Security Synchronization", replication of core database is optional. Depends on your needs. – Ian Apr 11 '17 at 12:20
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    Without a separate core database per region you database connections will have extra latency to travel back to the primary data centre, and you'll have a single point of failure (which might be one of the things you wanted to avoid when going active active) – Ian Apr 11 '17 at 12:23
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    Thank you for pointing that out! I do know that there are other things using the Core DB (for example WFFM stores file uploads in the Core DB to be processed on the CM), so we would need some kind of sync for sure. – Xuntar Apr 12 '17 at 7:25

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