scale up - vertically scale
scale out - horizontally scale
scale out
1. Use share nothing clustering architectures
The session failover functionality cannot avoid errors completely when failures happen, as my article mentioned, but it will damage the performance and scalability.
2. Use scalable session replication mechanisms
The most scalable one is paired node replication, the least scalable solution is using database as session persistence storage.
3. Use collocated deployment instead of distributed one.
4. Shared resources and services
Database servers, JNDI trees, LDAP Servers, and external file systems can be shared by the nodes in the cluster.
5. Memcached
Memcached's magic lies in its two-stage hash approach. It behaves as though it were a giant hash table, looking up key = value pairs. Give it a key, and set or get some arbitrary data. When doing a memcached lookup, first the client hashes the key against the whole list of servers. Once it has chosen a server, the client then sends its request, and the server does an internal hash key lookup for the actual item data.
6. Terracotta
Terracotta extends the Java Memory Model of a single JVM to include a cluster of virtual machines such that threads on one virtual machine can interact with threads on another virtual machine as if they were all on the same virtual machine with an unlimited amount of heap.
7. Using unorthodox approach to achieve high scalability
