Openstack Heat is an "orchestration tool" which is used to define a collection of virtual resources (Servers, networks, volumes, firewalls etc) which should be created in bulk. To define such a collection of resources you use text-files in a YAML format called the "Heat Orchestration Template", or HOT files. When a collection of resources is defined you can create one or more instances of that collection. A typical use-case can be to create a HOT-template describing a single lab-instance for a student-group, and then instantiate it multiple times to create multiple identical LAB scenarios.
Documentation
Heat is a large tool, with online documentation which is updated by the team developing Heat. The online documentation is found HERE, and it is recommended to familiarize yourself with it. It might be a bit overwhelming at first, so the guide on the following wiki-page might be a good starting-point to understand some of the Heat functionality.
Example-case
To demonstrate the use of heat we are going to create a virtual lab infrastructure consisting of two virtual servers connected to a single network. One of the servers should have an extra disk connected which it is going to share to the other using NFS, to demonstrate multiple bits of Heats functionality. We are going to create two Heat-templates for this example, one for some common resources needed by all the labs, and one for each server-pair. The following figure might help visualize the intended setup:
Common infrastructure
The common infrastructure is in this case a virtual network connected to a virtual switch. In addition we create a common firewall-group allowing traffic to/from our servers.
Base template structure
A heat-template is a YAML file, and the base structure looks something like so:
Basicly there is a block for inputs, a block for resources and a block for outputs.
Heat template for our common infrastructure
For our common infrastructure we do not need any inputs, but we would like to create som resources and give the ID of the created resources as output so that we can use them as inputs for other templates. This can result in a template looking like this:
Basically we are here telling heat to create a network for us (line 8-9) with a subnetwork connected to it (line 11-17). The subnetwork should use the address 192.168.0.0/24. Next up we create a router connected to the 'ntnu-internal' network, and attaching it to the newly created subnet. The final resource defined is a security-group allowing incoming ssh-connections from anywhere, incoming ICMP (ie: ping) from anywhere and incoming NFS-connections from any hosts at the supplied subnet.
Actually create the resources defined in our template
When a template is defined it is possible to use it to create a "heat stack". A "stack" is the resources created based on a template, and you can create multiple stacks using the same template if you want to have multiple copies of the same infrastructure. Creating the stack can be done through both the webinterface and the commandline-client. Even though most of this article will use the commandline we will also show the creation of the first stack through the webclient.
Creating a Heat Stack in the webinterface
To create a Heat stack in the webinterface you should navigate to "Orchestration → Stacks" and click the "Launch Stack" button. There you can either select template-files from your computer, or you can paste the templates into text-fields.
After a little bit of time the stack should be "Create Complete", and you can now browse the networks/routers/security group pages to see the newly created resources.
Creating a Heat Stack using the command line
Creating a heat-stack using the commandline is done through the use of a single "openstack stack create" command. The stacks can be listed afterwards using the "openstack stack list" command.