The Stackato VM is a stand-alone micro cloud virtual machine with all the components necessary for running a test environment in one instance. For use on a larger scale, the VM can be cloned and assigned specific roles: Router, Cloud Controller, Droplet Execution Agents (DEAs, or worker nodes), Stager, or specific database services.
The router directs incoming network traffic to the appropriate application.
For smaller configurations, the router can be run on the same 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.
The primary node is the main entry point for a Stackato setup. It is a mandatory part of a Core node and runs a number of system critical processes.
In a cluster setup, this will be the node that nodes performing other roles are attached to. Every cluster must include exactly one Primary node.
The base role comprises of several processes that are necessary for any node to function as part of a stackato cluster, and is mostly responsible for communicating with the primary node and forwarding log information.
This role cannot be disabled on any node.
The Controller manages most of the operations of a Stackato system. It hosts the Management Console, provides the API endpoint for client access, manages the cloud_controller process, provisions services, dispatches applications for staging and deployment, and (with the Health Manager) tracks the availability of DEA nodes.
In the case of a cluster setup, it resides 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 neccessary for larger implementations.
DEAs run on multiple nodes and receive requests from the Cloud Controller(s) to start staged applications.
As traffic increases, additional Stackato VMs can be configured as DEAs in order to reduce the load on each of them and to allow applications to be pushed to more than one instance.
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.
The stager provides the runtime dependency requirements to the droplet before it is run, such as those from PyPy, PPM and NPM or staging hooks.
For some applications, this can include compiling libraries or other programs, which can be demanding on system resources. Running a separate staging node on a dedicated instance, or running multiple stagers, can balance the load on a Stackato cluster that sees frequent deployments or application updates.
Stackato nodes can also be assigned roles for data services. The data services can be run separately on their own nodes, or grouped together.
Note
Data services running on on Amazon EC2 instances should be backed by persistent storage on an EBS (Elastic Block Store) volume. See Persistent storage for /var/vcap for details.
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.