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We tested this out here at THG (a bit too late as we'd already deployed multiple regions). What we did was install a stretched galera cluster across multiple DCs with clustered proxysql fronting it so we could force writes to a single node. We then deployed
keystone in each regions on top of this. We put keysone behind a geo-loadbalancer so each region would prefer talking to their local keystones and proxy sql would force writes to a single node in the stretched cluster avoiding issues with commit latency and
deadlocks. </div>
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Horizon doesn't need to exist in a single region, it can exist in all regions as long as it has api connectivity to all regions endponts and the "global" keystone. </div>
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If you are using kolla we found it easier to have a specific deployment for keystone only and then each region had it's normal deployment but with a remote keystone.</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> wodel youchi <wodel.youchi@gmail.com><br>
<b>Sent:</b> 23 May 2023 14:02<br>
<b>To:</b> OpenStack Discuss <openstack-discuss@lists.openstack.org><br>
<b>Subject:</b> multi-region deployment</font>
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<div class="x_caution" style="background-color:#F47F53; font-family:sans-serif"><span style="font-size:14pt"><strong>CAUTION:</strong></span>
<span style="font-size:11pt; font-weight:400">This email originates from outside THG</span>
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Hi,</div>
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<div>I have been reading about multi-region in openstack.</div>
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<div>From my understanding, that keystone and horizon are shared and deployed only in the first region.<br>
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<div>Is this correct? If yes, what happens if the first region goes down?<br>
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<div>Regards.<br>
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