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Environments

The environment is used to affect the runtime behaviour of the template. It provides a way to override the default resource implementation and the parameters passed to Heat.

To fully understand the runtime behavior you also have to consider what plug-ins the cloud provider has installed.

Format

It is a yaml text file with two main sections "resource_registry" and "parameters".

Command line usage

heat stack-create my_stack -e my_env.yaml -P "some_parm=bla" -f my_tmpl.yaml

Global and effective environments

The environment used for a stack is the combination of (1) the environment given by the user with the template for the stack and (2) a global environment that is determined by the cloud provider. Combination is asymmetric: an entry in the first environment takes precedence over an entry in the second. The OpenStack software includes a default global environment, which supplies some resource types that are included in the standard documentation. The cloud provider can add additional environment entries.

The cloud provider can add to the global environment by putting environment files in a configurable directory wherever the heat engine runs. The configuration variable is named "environment_dir" and is found in the "heat.common.config" module (AKA the "[DEFAULT]" section) of "/etc/heat/heat.conf". The default for that directory is "/etc/heat/environment.d". Its contents are combined in whatever order the shell delivers them when the heat engine starts up, which is the time when these files are read.

If the "my_env.yaml" file from the example above had been put in the "environment_dir" then the user's command line could be this:

heat stack-create my_stack -P "some_parm=bla" -f my_tmpl.yaml

Usage examples

1) Pass parameters into Heat

parameters:
  KeyName: heat_key
  InstanceType: m1.micro
  ImageId: F18-x86_64-cfntools

2) Deal with the mapping of Quantum to Neutron

resource_registry:
  "OS::Quantum*": "OS::Neutron*"

So all existing resources which can be matched with "OS::Neutron*" will be mapped to "OS::Quantum*" accordingly.

3) Override a resource type with a custom template resource

resource_registry:
  "AWS::EC2::Instance": file:///home/mine/my_instance_with_better_defaults.yaml

Please note that the template resource URL here must end with ".yaml" or ".template", or it will not be treated as a custom template resource.

4) Always map resource type X to Y

resource_registry:
  "OS::Networking::FloatingIP": "OS::Nova::FloatingIP"

5) Use default resources except one for a particular resource in the template

resource_registry:
  resources:
    my_db_server:
      "OS::DBInstance": file:///home/mine/all_my_cool_templates/db.yaml

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