Application Description Template

MiCADO executes applications described by Application Description Templates (ADT). The ADT is based on the TOSCA Specification and is described in detail in this section. Some familiarity with YAML is helpful.

An ADT describes the following aspects of an application, which are documented individually:

• Containers
• Volumes & Configs
• Virtual Machines
• Monitoring
• Scaling
• Networking
• Secrets

Overview

• Application Description Templates are the domain specific language of MiCADO.

• They describe the container, virtual machine and scaling/security policies that make up an application deployment.

• These different sections of the ADT get translated and orchestrated by the relevant underlying tools in MiCADO.

A quick look...

ADTs are based on TOSCA, written in YAML and you can start writing one like this:

tosca_definitions_version: tosca_simple_yaml_1_3

imports:
  - https://github.com/micado-scale/tosca/main/micado_types.yaml

description: ADT for stressng on EC2

Next up, the topology_template is where you describe your containers, virtual machines and policies, beginning with container and virtual machines under node_templates like so:

topology_template:
  node_templates:

    app-container:
      type: tosca.nodes.MiCADO.Container.Application.Docker
      properties:
        image: uowcpc/nginx:v1.2
      interfaces:
        Kubernetes:
          create:
            inputs:
              kind: Deployment


    worker-virtualmachine:
      type: tosca.nodes.MiCADO.EC2.Compute
      properties:
        instance_type: t2.small
      interfaces:
        Terraform:
          create:

A closer look...

• Looking above, you can see we use a specific type to let our adaptors know what they are looking at.

• You can think of properties as providing the options and parameters specific to the basic resource that you want to orchestate (above, the Docker container, and the EC2 compute instance).

• The interfaces section, on the other hand, specifies the orchestrator that should be used to manage the defined resouce, with the option to pass in options and parameters for that tool (above, Kubernetes and Terraform).

Main sections

The main sections of an ADT are documented below.

tosca_definitions_version

string. Default: tosca_simple_yaml_1_3. The version of TOSCA to work with. v1.3 by default.

imports

string[ ]. List of urls pointing to custom TOSCA types. The default url points to the custom types defined for MiCADO. Please, do not modify this url.

topology_template

map. The body of the application description.

node_templates

map. Definitions of application containers and auxiliary components such as volumes and virtual machines.

policies

map. Scaling & metric policies.

types

This section is used to optionally define additional detailed types which can be referenced in the topology_template section to benefit from abstraction. Under policy_types: for example, complex scaling logic can be defined here, then referenced in the policies section above