This version is still under development! Latest stable release is v0.3.2

Extending tools

Extending the existing STACKL toolset can be achieved by creating a subclass of the base-handler and implementing its abstract methods.

Specifically, every subclass needs to implement the following:

  • Class constructor
  • create_command_args method
  • delete_command_args method

Handler class

As described above, every handler class consists out of a constructor and two methods. In the constructor we define all the objects we need for our Kubernetes job and in the create and delete methods we define the arguments we want to pass to the tool for creation and deletion.

Constructor

The constructor is used to create all the necessary Kubernetes objects used by the base handler. Each object will be described in a subsection.

Secret handler

The secret handler is an object of the class SecretHandler. This class is an abstract class, so the object has to be a child class of SecretHandler. This object is optional, if no secrets are used, a secret handler has no function. More information about secret handlers.

Output

The output object handles output for the handler. For more information, visit output documentation.

Environment list

The enviornment list is a dictionary containing environment variables and their values necessary for a handler. These environment variables are added to the Kubernetes job. For example:

self._env_list = {
    "ANSIBLE_INVENTORY_PLUGINS": "/opt/ansible/plugins/inventory",
    "ANSIBLE_INVENTORY_ANY_UNPARSED_IS_FAILED": "True"
}

These variables point to the custom STACKL inventory script for Ansible and make sure that when the inventory parsing fails the job also fails.

Volumes

Volumes is an array containing dictionaries that define Kubernetes volumes. The following table describes every attribute of the dictionary:

VariableDescriptionRequiredValues
nameName of the volumeyes
typeType of the volumeyesempty_dir/config_map
dataData to add to the volume. Used in conjunction with config_map typeyes, when type==config_mapAny dictionary
mounth_pathPath to mount the volume to. Each volume is mounted to every container in the jobyes
sub_pathA sub path in the mount pathno

For example:

self._volumes = [{
    "name": "inventory",
    "type": "config_map",
    "mount_path": "/opt/ansible/playbooks/inventory/stackl.yml",
    "sub_path": "stackl.yml",
    "data": {
        "stackl.yml": json.dumps(self._secret_handler.stackl_inv)
    }
}]

Init containers

A list of init containers can be added to a handler. Each init container is a dictionary. The following table describes every attribute of the dictionary:

VariableDescriptionRequired
nameName of the init containeryes
imageImage for the init containeryes
argsArgs for the init container commandno

Command

The command for the Kubernetes job. The command together with its arguments defines what a handler needs to do when creating, updating or deleting a stack instance. The command is a list of strings.

For example:

self._command = ["ansible"]

Create command args

create_command_args is an abstract method of the base_handler class. This method is a property that has no parameters except for self and returns a list of strings.

Together with the command property of the class, these arguments define what command a Kubernetes job will execute when a stack instance of this type is created.

For example:

@property
def create_command_args(self) -> List[str]:
  self._command_args[0] = f'ansible-playbook \
                          {self.provisioning_parameters["ansible_playbook_path"]} \
                          -v -i /opt/ansible/playbooks/inventory/stackl.yml'
  return self._command_args

Delete command args

As the create_command_args method, the delete_command_args method is an abstract method of the base_handler class. This method is a property that has no parameters except for self and returns a list of strings.

For example:

@property
def delete_command_args(self) -> List[str]:
    """The command arguments used in a job to delete something with Ansible
    :return: A list with strings containing shell commands
    :rtype: List[str]
    """
    self._delete_command_args = self.create_command_args
    self._delete_command_args[0] += ' -e state=absent'
    return self._delete_command_args

Last updated on December 11, 2020