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Jelastic has been a popular multi-container PaaS solution for Java developments offering support for GlassFish among other container choices.
It now fully supports the GlassFish 3.1.x clustering DAS-based architecture with horizontal scaling and session replication, both of which leverage Jelastic's NGINX-based load-balancing service.
Have you tried GlassFish running on Jelastic? What was the experience like?