deb-murano/doc/source/articles/workflow.rst

Murano workflow

What happens when a component is being created in an environment? This document will use the Telnet package referenced elsewhere as an example. It assumes the package has been previously uploaded to Murano.

Step 1. Begin deployment

The API sends a message that instructs murano-engine, the workflow component of Murano, to deploy an environment. The message consists of a JSON document containing the class types required to create the environment, as well as any parameters the user selected prior to deployment. Examples are:

• An Environment object (io.murano.Environment) with a name
• An object (or objects) referring to networks that need to be created or that already exist
• A list of Applications (e.g. io.murano.apps.linux.Telnet). Each Application will contain, or will reference, anything it requires. The Telnet example, has a property called instance whose contract states it must be of type io.murano.resources.Instance. In turn the Instance has properties it requires (like a name, a flavor, a keypair name).

Each object in this model has an ID so that the state of each can be tracked.

The classes that are required are determined by the application's manifest. In the Telnet example <telnet-example> only one class is explicitly required; the telnet application definition.

The Telnet class definition <telnet-example> refers to several other classes. It extends Application and it requires an Instance. It also refers to the Environment in which it will be contained, sends reports through the environment's status-reporter and adds security group rules to the security-group-manager.

Step 2. Load definitions

The engine makes a series of requests to the API to download packages it needs. These requests pass the class names the environment will require, and during this stage the engine will validate that all the required classes exist and are accessible, and will begin creating them. All Classes whose workflow sections contain an initialize fragment are then initialized. A typical initialization order would be (defined by the ordering in the model sent to the murano-engine):

• Network
• Instance
• Object
• Environment

Step 3. Deploy resources

The workflow defined in Environment.deploy is now executed. The first step typically is to initialize the messaging component that will pay attention to murano-agent (see later). The next stage is to deploy each application the environment knows about in turn, by running deploy() for each application. This happens concurrently for all the applications belonging to an instance.

In the Telnet example <telnet-example> (under Workflow), the workflow dictates sending a status message (via the environment's reporter, and configuring some security group rules. It is at this stage that the engine first contacts Heat to request information about any pre-existing resources (and there will be none for a fresh deploy) before updating the new Heat template with the security group information.

Next it instructs the engine to deploy the instance it relies on. A large part of the interaction with Heat is carried out at this stage; the first thing an Instance does is add itself to the environment's network. Since the network doesn't yet exist, murano-engine runs the neutron network workflow which pushes template fragments to Heat. These fragments can define: * Networks * Subnets * Router interfaces

Once this is done the Instance itself constructs a Heat template fragment and again pushes it to Heat. The Instance will include a userdata script that is run when the instance has started up, and which will configure and run murano-agent.

Step 4. Software configuration via murano-agent

If the workflow includes murano-agent components (and the telnet example does), typically the application workflow will execute them as the next step.

In the telnet example, the workflow instructs the engine to load DeployTelnet.yaml as YAML, and pass it to the murano-agent running on the configured instance. This causes the agent to execute the EntryPoint defined in the agent script (which in this case deploys some packages and sets some iptables rules).

Step 5. Done

After execution is finished, the engine sends a last message indicating that fact; the API receives it and marks the environment as deployed.