Multi-VM Workflows on

Overview

Mon, 17 Feb 2025 00:00:00 +0000

How Should I Read This Chapter

Some applications require multiple VMs to implement their workflow. OpenNebula allows you to coordinate the deployment and resource usage of such applications through the OneFlow component.

This component is able to deploy services; these services are a group of interconnected Virtual Machines that work as an entity. They can communicate with each other using Virtual Networks deployed by the OneFlow server itself, and they can also have some relationship. A group of Virtual Machines, known as a Role, can depend on other Roles, so it will be deployed when the parent is ready.

OneFlow Services Management

Mon, 17 Feb 2025 00:00:00 +0000

OneFlow allows users and administrators to define, execute, and manage multi-tiered applications, which we call Services, composed of interconnected Virtual Machines with deployment dependencies between them. Each group of Virtual Machines is deployed and managed as a single entity and is completely integrated with the advanced OpenNebula user and group management.

What Is a Service

The following diagram represents a multi-tier application. Each node represents a Role and its cardinality (the number of VMs that will be deployed). The arrows indicate the deployment dependencies: each Role’s VMs are deployed only when all its parent’s VMs are running.

OneFlow Services Auto-scaling

Mon, 17 Feb 2025 00:00:00 +0000

A Service Role’s cardinality can be adjusted either manually or automatically in two ways: based on metrics or based on a schedule.

Overview

When a scaling action starts, the Role and Service enter the SCALING state. In this state, the Role will instantiate or terminate a number of VMs to reach its new cardinality.

A Role with elasticity policies must define a minimum and maximum number of VMs:

OneGate Usage

Mon, 17 Feb 2025 00:00:00 +0000

The OneGate component allows Virtual Machine guests to pull and push VM information from OpenNebula. Users and administrators can use it to gather metrics, detect problems in their applications, and trigger OneFlow elasticity rules from inside the VM.

For Virtual Machines that are part of a Multi-VM Application (OneFlow Service), they can also retrieve the Service information directly from OneGate and trigger actions to reconfigure the Service or pass information among different VMs.