Roles
Base
The Base role comprises of several processes that are necessary for any node to
function as part of a Helion Stackato cluster, and is mostly responsible for
communicating with the primary node and forwarding log information.
This role cannot be disabled on any node.
Primary
The Primary role is a mandatory part of a core node (or micro cloud) and
runs a number of critical system processes, including the Cloud
Controller, Health Manager, and a Router.
The Health Manager keeps track of the apps on each DEA and provides
feedback on the number currently running. It works in conjunction with
the Cloud Controller and must be run on the same VM.
In a cluster setup, all nodes performing other roles are attached to the MBUS IP
of the core node. Every cluster must include exactly one Primary role.
Note
The Router role must be run along with the Primary even if there are
other Routers in the cluster and the node is not exposed to the
internet.
Cloud Controller
The Controller manages most of the operations of a Helion Stackato
system. It hosts the Management Console, provides the API endpoint for
client access, manages the cloud_controller_ng process, provisions services,
dispatches applications for staging and deployment, and (with the Health Manager)
tracks the availability of DEA nodes.
In a cluster setup, the Controller role must run on the core node that all other VM's in the cluster connect to.
A single Controller is sufficient for small and mid-sized
clusters, but multiple Controllers
can be configured if necessary for larger implementations.
Router
The router directs incoming network traffic to the appropriate application.
For smaller configurations, the router can be run on the same Helion Stackato VM as
the other components.
When additional DEAs are in use and traffic increases, additional
routers can be added to handle the load. This will require a load
balancer to be available in the cluster.
Droplet Execution Agents
The Droplet Execution Agent (DEA) role in Helion Stackato is responsible for
staging applications and running application instances within Linux
containers. In a Helion Stackato cluster, there will typically be a number of
nodes running the DEA role, which in turn each host multiple user
application instances.
The Cloud Controller allocates instances of an application across
available DEA nodes, prioritizing eligible nodes that are running the
fewest instances of that app already. This maintains an even
distribution of instances of an app across the pool.
The DEA role is comprised of a number of processes:
- dea_ng: Master process for staging and starting application
instances, reporting on their state via NATS to the Health Manager.
- dir_server: Handles requests for directories/files, responding with
an HTTP URL.
- fence: Responsible for the management of application containers using
Docker.
- apptail: Streams application logs via Logyard to various log drains.
The Docker image used for the containers can be customized by
admins.
Role Groups
Role groups represent a set of roles. For example the data-services
group provides all databases plus RabbitMQ and the filesystem service:
$ kato role add data-services
Additional groups can be defined by administrators in
/s/etc/kato/role_groups.yml.
