November 21, 2018
OpenStack enables automated creation of resources such as networks, routers, and servers using Heat Orchestration Templates. If you are new to OpenStack and are using a TripleO based distribution you may have seen them up close and personal without knowing it. What follows is a very basic exploration of Heat.
Heat templates are written in YAML format, and you can quickly see from the documentation that a basic template will likely have 4 sections:
# templates will use features as of this release of OpenStack
heat_template_version: queens
...
# variables to inform the creation of resources to follow
parameters:
...
# the things the template will be creating
resources:
...
# information about the things that were created
outputs:
...
The heat_template_version specifies the features expected to be supported by the template to follow. You may see dated versions, but since Newton the release name is supported. I would use that if the template is not going to be used on a cloud older than that.
The parameters section identifies any variables that will be used later in the template. This is where a place holder for a server name, or the flavor to use would be defined. Parameters can have a default value and miscellaneous constraints applied for validation.
Objects like a server instance are known as resources. Anything that the template will create or instantiate will be listed in the resources section and will be informed by the parameters section.
Once a template has been “launched” or fed to OpenStack it will create what is called a stack of all the resources requested. There are likely some obvious questions you want to ask about a stack like: “What is the name of the server I just created?” or “What is the IP of my server?”. The outputs section makes it easy to expose that information.
Simple Example Template
Here is a template that will create a server and attach it to a network, but it assumes that a network exists. In my case I already have a network named provider192.
# file: example-1.yaml
# i never plan to run on OpenStack < Queens
heat_template_version: queens
description: Create a server instance
parameters:
# define a variable named "image" to use later
image:
description: Name of image from Glance to create an instance from.
type: string
# Do you have an image named this already?
default: cirros-0.4.0.raw
flavor:
description: Instance flavor to build.
type: string
# Do you have a flavor named this already?
default: m1.small
constraints:
# only accept valid flavors for this parameter
- custom_constraint: nova.flavor
resources:
# create a resource named "my_instance"
my_instance:
# the my_instance resource is a server
type: OS::Nova::Server
properties:
# use the image parameter / variable defined above
image: { get_param: image }
flavor: { get_param: flavor }
outputs:
name:
description: The name of the server created in this stack.
value: { get_attr: [ my_instance, name ] }
Create Example-1 Stack with Defaults
Save that to a file called example-1.yaml. Edit the default flavor and image values to match what exists in your cloud.
Now create a stack from the template. The command looks like this:
$ openstack stack create -t <template_filename.yaml> <resultant_stack_name>
$ openstack stack create -t example-1.yaml example-1
+---------------------+--------------------------------------+
| Field | Value |
+---------------------+--------------------------------------+
| id | 218fedd6-efdd-4c2b-ac82-7f15bf1c4235 |
| stack_name | example-1 |
| description | Create a server instance |
| creation_time | 2018-11-22T00:21:16Z |
| updated_time | None |
| stack_status | CREATE_IN_PROGRESS |
| stack_status_reason | Stack CREATE started |
+---------------------+--------------------------------------+
Wait a minute or two, and then list the stack and see what outputs it can show us.
$ openstack stack list
+--------------------------------------+------------+-----------------+----------------------+--------------+
| ID | Stack Name | Stack Status | Creation Time | Updated Time |
+--------------------------------------+------------+-----------------+----------------------+--------------+
| 218fedd6-efdd-4c2b-ac82-7f15bf1c4235 | example-1 | CREATE_COMPLETE | 2018-11-22T00:21:16Z | None |
+--------------------------------------+------------+-----------------+----------------------+--------------+
$ openstack stack output list example-1
+------------+-----------------------------------------------+
| output_key | description |
+------------+-----------------------------------------------+
| name | The name of the server created in this stack. |
+------------+-----------------------------------------------+
That looks familiar, what does it contain?
$ openstack stack output show example-1 name
+--------------+-----------------------------------------------+
| Field | Value |
+--------------+-----------------------------------------------+
| description | The name of the server created in this stack. |
| output_key | name |
| output_value | example-1-my_instance-omfgcgk3w7nd |
+--------------+-----------------------------------------------+
There is the name of the server we just created! How about something more to the point for use in a script.
$ openstack stack output show example-1 name -f value -c output_value
example-1-my_instance-omfgcgk3w7nd
Take a look at the whole stack.
$ openstack stack show example-1
+-----------------------+-------------------------------------------------------------------------------------------------------------------------------------+
| Field | Value |
+-----------------------+-------------------------------------------------------------------------------------------------------------------------------------+
| id | 218fedd6-efdd-4c2b-ac82-7f15bf1c4235 |
| stack_name | example-1 |
| description | Create a server instance |
| creation_time | 2018-11-22T00:21:16Z |
| updated_time | None |
| stack_status | CREATE_COMPLETE |
| stack_status_reason | Stack CREATE completed successfully |
| parameters | OS::project_id: 1686c505946841259bfda1f1c206456d |
| | OS::stack_id: 218fedd6-efdd-4c2b-ac82-7f15bf1c4235 |
| | OS::stack_name: example-1 |
| | flavor: m1.small |
| | image: cirros-0.4.0.raw |
| | |
| outputs | - description: The name of the server created in this stack. |
| | output_key: name |
| | output_value: example-1-my_instance-omfgcgk3w7nd |
| | |
| links | - href: https://openstack.example.com:13004/v1/1686c505946841259bfda1f1c206456d/stacks/example-1/218fedd6-efdd-4c2b-ac82-7f15bf1c4235|
| | rel: self |
| | |
| parent | None |
| disable_rollback | True |
| deletion_time | None |
| stack_user_project_id | 4b22b80f4a1843f7a90b13e54375b4d5 |
| capabilities | [] |
| notification_topics | [] |
| tags | None |
| timeout_mins | None |
| stack_owner | None |
+-----------------------+-------------------------------------------------------------------------------------------------------------------------------------+
And now at the server it created. Notice that it attached to a network I had already created, named provider192.
$ openstack server show example-1-my_instance-omfgcgk3w7nd
+-----------------------------+----------------------------------------------------------+
| Field | Value |
+-----------------------------+----------------------------------------------------------+
| OS-DCF:diskConfig | MANUAL |
| OS-EXT-AZ:availability_zone | nova |
| OS-EXT-STS:power_state | Running |
| OS-EXT-STS:task_state | None |
| OS-EXT-STS:vm_state | active |
| OS-SRV-USG:launched_at | 2018-11-22T00:21:31.000000 |
| OS-SRV-USG:terminated_at | None |
| accessIPv4 | |
| accessIPv6 | |
| addresses | provider192=192.0.2.14 |
| config_drive | |
| created | 2018-11-22T00:21:22Z |
| flavor | m1.small (af20508a-5986-4bf3-9e9f-33ca598e1563) |
| hostId | f1e7461e138a94335e579cb81cd95933fc3879b263a3109281d203ba |
| id | ce6e7e7a-f091-4fe8-bde0-b0ae3d3664d7 |
| image | cirros-0.4.0.raw (a034ee47-4642-4d21-9b08-11774808a822) |
| key_name | None |
| name | example-1-my_instance-omfgcgk3w7nd |
| progress | 0 |
| project_id | 1686c505946841259bfda1f1c206456d |
| properties | |
| security_groups | name='default' |
| status | ACTIVE |
| updated | 2018-11-22T00:21:31Z |
| user_id | e2041d2848be40f6b6fb86709b260ae1 |
| volumes_attached | |
+-----------------------------+----------------------------------------------------------+
Throw away this stack. This will delete the stack and any resources it created, such as the example-1-my_instance-omfgcgk3w7nd server.
$ openstack stack delete example-1 --yes
Create Example-1 Stack with Supplied Parameters
Let’s see how to pass in parameter values and demonstrate the effect of the custom constraint we placed on the flavor parameter.
We know there is a parameter named flavor we can provide a value to override the default value when we create a stack from our template.
# flawed example
$ openstack stack create -t example-1.yaml --parameter flavor=nonexistant example-fail
ERROR: Parameter 'flavor' is invalid: Error validating value 'nonexistant': No Flavor matching {'name': u'nonexistant'}. (HTTP 404)
Since the flavor was not found, our stack was not created. In truth, without that custom constraint a similar error would have been produced.
# flawed example with custom constraint removed
$ openstack stack create -t example-1.yaml --parameter flavor=nonexistant example-fail
ERROR: Property error: : resources.my_instance.properties.flavor: : Error validating value 'nonexistant': No Flavor matching {'name': u'nonexistant'}. (HTTP 404)
Of course if you pass the name of a flavor that exists in your cloud there will be no error.
# example with custom constraint removed
$ openstack stack create -t example-1.yaml --parameter flavor=m1.large example-1
Create Example-1 Stack with Environment File
Instead of passing the parameters on the command line you can also use what is called an environment file. An environment file should include a parameter_defaults section containing the parameters it will define and the values to supply. For example, this will provide a new value for the flavor parameter when coupled with our example-1.yaml template.
# file: environment-1.yaml
parameter_defaults:
flavor: m1.medium
Make sure the stack is gone and then recreate it with the above environment file.
$ openstack stack delete example-1 --yes
$ openstack stack create -t example-1.yaml -e environment-1.yaml example-1
+---------------------+--------------------------------------+
| Field | Value |
+---------------------+--------------------------------------+
| id | 06fbdce6-5ac5-49b0-be54-7766fd1afdef |
| stack_name | example-1 |
| description | Create a server instance |
| creation_time | 2018-11-22T01:48:03Z |
| updated_time | None |
| stack_status | CREATE_IN_PROGRESS |
| stack_status_reason | Stack CREATE started |
+---------------------+--------------------------------------+
See what resources the stack created.
$ openstack stack resource list example-1
+---------------+--------------------------------------+------------------+-----------------+----------------------+
| resource_name | physical_resource_id | resource_type | resource_status | updated_time |
+---------------+--------------------------------------+------------------+-----------------+----------------------+
| my_instance | 90794a87-7db8-4220-a1c9-6f2e4b68429b | OS::Nova::Server | CREATE_COMPLETE | 2018-11-22T01:48:04Z |
+---------------+--------------------------------------+------------------+-----------------+----------------------+
Remember my_instance is the name of the Heat resource not the Nova server, but the physical_resource_id is the UUID of the server.
What flavor is that server instance? Instead of the default m1.small, it should be m1.medium per our environment file.
$ openstack server show 90794a87-7db8-4220-a1c9-6f2e4b68429b -c flavor -c name
+--------+--------------------------------------------------+
| Field | Value |
+--------+--------------------------------------------------+
| flavor | m1.medium (fa4efbb9-6f43-4a29-aa1a-fa1069681ad6) |
| name | example-1-my_instance-c3pg4dyb5l6n |
+--------+--------------------------------------------------+
Bingo!
I hope this basic example of using Heat Orchestration Templates was informative. I’ll try to follow up with some more comprehensive examples. Check back in a week or two!
See Also
Some helpful blogs and documentation
- Rackspace OpenStack Orchestration In Depth, Part I: Introduction to Heat
- OpenStack Resource Types
- OpenStack User Guide Create and Manage Stacks
- HOT Template Specification
- OpenStack Resource Types - Go here when looking up resource parameters and outputs.
- TripleO Documentation
- Heat Template Composition
- Stratoscale Best Practices for OpenStack Heat Templates
- DevOpsPro 2016 is a great tutorial by example!
- Heat 101 by gchenuet