Services perform functions essential to the health or functionality of the system. For example, the Metrics service stores and manages system events, while the Watchdog service ensures that other services remain running. Internally, services run in Docker containers on the instances in the system.
Services are grouped into these categories depending on what actions they perform:
- Services: Enable product functionality. For example, the Index service performs functions that allow the system to be used to search for data. You can scale, move, and reconfigure these services.
- System services: Maintain the health and availability of the system. You cannot scale, move, or reconfigure these services.
Some System services run only on master instances.
Some services are classified as applications. These are the services with which users interact. Services that are not applications typically interact only with other services.
Services run on instances in the system. Most services can run simultaneously on multiple instances. That is, you can have multiple instances of a service running on multiple instances in the system. Some services run on only one instance.
Each service has a best and required number of instances on which it should run.
You can configure where Hitachi Content Intelligence services run, but not system services.
Some services can have multiple service instance types. That is, a service can run on two system instances, but those two service instances can perform different functions from one another.
For example, the Clustered-File-System service, which gives other services locations for storing data, has three instance types: Name Node, Journal Node, and Data Node.
If a service supports floating, you have flexibility in configuring where new instances of that service are started when service instances fail.
Non-floating (or persistent) services run on the specific instances that you specify. If one of those service instances fails, the system does not automatically bring up a new instance of that service on another system instance.
With a service that supports floating, you specify a pool of eligible system instances and the number of service instances that should be running at any time. If a service instance fails, the system brings up another one on one of the system instances in the pool that doesn't already have an instance of that service running.
For services with multiple types, the ability to float can be supported on a per-type basis.
Each service binds to a number of ports and to one type of network, either internal or external. Networking for each service is configured during system installation and cannot be changed after a system is running.
Services can use volumes for storing data.