31 lines
1.8 KiB
Text
31 lines
1.8 KiB
Text
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[[_replication]]
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=== Replication and Failover
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There are caches like `sessions`, `authenticationSessions`, `offlineSessions`, `loginFailures` and a few others (See <<_eviction>> for more details),
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which are configured as distributed caches when using a clustered setup. Entries are
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not replicated to every single node, but instead one or more nodes is chosen as an owner of that data. If a node is not the owner of a specific cache entry it queries
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the cluster to obtain it. What this means for failover is that if all the nodes that own a piece of data go down, that data
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is lost forever. By default, {project_name} only specifies one owner for data. So if that one node goes down
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that data is lost. This usually means that users will be logged out and will have to login again.
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You can change the number of nodes that replicate a piece of data by change the `owners` attribute in the `distributed-cache` declaration.
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.owners
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[source,xml,subs="attributes+"]
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----
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<subsystem xmlns="{subsystem_infinispan_xml_urn}">
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<cache-container name="keycloak">
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<distributed-cache name="sessions" owners="2"/>
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...
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----
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Here we've changed it so at least two nodes will replicate one specific user login session.
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TIP: The number of owners recommended is really dependent on your deployment. If you do not care if users are logged
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out when a node goes down, then one owner is good enough and you will avoid replication.
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TIP: It is generally wise to configure your environment to use loadbalancer with sticky sessions. It is beneficial for performance
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as {project_name} server, where the particular request is served, will be usually the owner of the data from the distributed cache
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and will therefore be able to look up the data locally. See <<sticky-sessions>> for more details.
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