Distributed sessions

[rymsha]

Thanks to Hazelcast jetty sessions can be distributed.

Need to cover a few use cases:

• no sticky sessions configured
• sticky sessions configured on /
• sticky sessions configured on specific path (i.e. /admin)

[rymsha]

Hazelcast distributed sessions are enabled by storeMode = replicated parameter in com.enonic.xp.web.sessionstore.cfg
In this mode all sessions are available on all XP nodes where storeMode = replicated is enabled.

• It mitigates problem of lost sessions when one node is restarted (because persistent sessions gracefully migrate to other nodes)
• It also mitigates problem of lost sessions when one node is crashed (because persistent sessions have replicas)
• it simplifies load-distribution over nodes (in some cases)

LB sticky sessions are turned off:
In order to work correctly sessions must be persisted as soon as they get created and as soon as they are responded:

saveOnCreate = true
flushOnResponseCommit = true

LB sticky sessions are turned on on root context (/):

For performance reasons it may be good idea to minimize session persistence (this is default setting)

saveOnCreate = false
flushOnResponseCommit = false

However any long living request (i.e. long-polling, SSE, websocket?) within a session may not allow session to be persisted and session may be lost when session-initiating server crashes.

LB sticky sessions are turned on on specific path (i.e. /admin):

Is currently not recommended, because XP supports session cookie only on root path. Session cookie can then be created when user visits /admin pages, and stay with user even while she visits other paths.

Anyway to work properly persistence settings should be same as in case of sticky sessions turned off.

saveOnCreate = true
flushOnResponseCommit = true

For configurations without long living requests it may be sufficient to persist sessions only on create

saveOnCreate = true
flushOnResponseCommit = false

[sigdestad]

How does this relate to enabing Hazelcast + controlling which nodes may hold the actual distributed data (aka data=true)

[rymsha]

It doesn't. Why?