Diff. b/w Stateful / Stateless Services for HA

What is different between stateful and stateless services for High Availability Technologies.

Stateful:

• An action typically comprises multiple requests
• Data needs to be replicated and synchronized between redundant services (to preserve state and consistency)
• For example on Openstack services for stateful  MySQL, RabbitMQ, Cinder Volume, Ceilometer center agent, Neutron L3, DHCP agents, etc.

Stateless:

• There is no dependency between requests
• No need for data replication/synchronization. Failed request may need to be restarted on a different node.
• For example on Openstack for stateless services  Nova-api, nova-conductor, glance-api, keystone-api, neutron-api, nova-scheduler, Apache web server, Cinder Scheduler, etc.