*** dsn.dist.service.meta_server ** is a shared components of the service frameworks for both stateless and stateful services. It focuses on three aspects:

• membership management: what are the services/service partitions, what are the target machines for each partition, and what are their roles (e.g., worker, secondary, primary)

• machine pool management and failure detection: what are the machines to be deployed with the services, and whether they are healthy

• load balance: move the partition instances across machines so that the load is balanced across machines

Using the dsn.svchost to create an meta service instance after loading dsn.dist.service.meta_service, then it is done.

[modules]
dsn.dist.service.meta_server

[apps.meta]
type = meta
arguments = 
ports = %port%
pools = THREAD_POOL_DEFAULT,THREAD_POOL_META_SERVER,THREAD_POOL_FD,THREAD_POOL_META_STATE

Daemons or replica servers need to specify the meta server address in their configuration file to join the machine pool.

[meta_server]
server_list = <meta-server1,meta-server2>

Clients accessing the services also need to specify the meta server addresses, see dsn.dist.uri.resolver for more information.

We now use zookeeper to store the membership state as well as leader election from a set of meta servers to ensure service availability and reliability. Upon development, we use a stand-alone meta server which simply uses local disk file for state reliability. Two provider interfaces, distributed_lock_service and meta_state_service, are abstracted. Developers can therefore build their own for better quality in the future.

You can implement your own server_load_balancer instance, and plug them into the meta server.

register_component_provider("simple_load_balancer", replication::server_load_balancer::create<replication::simple_load_balancer>);
register_component_provider("greedy_load_balancer", replication::server_load_balancer::create<replication::greedy_load_balancer>);

Then specify them upon deployment.

[meta_server]
server_load_balancer_type = <cutomized server load balancer type>