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Fabric (SSH) Plugin

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You can use the Fabric plugin to map operations to SSH commands or Fabric tasks that are included in your blueprint.

The plugin provides an agentless method for running operations on destination hosts. The source code for this plugin is found in github.

Plugin Requirements:

• Python versions:
  • 2.7.x
• If access to the Context Proxy (ctx) is required within an invoked script, the remote host must have Python’s argparse installed.

Execution Methods

There are four modes for working with this plugin.

• Executing a list of commands.
• Executing a Fabric task from a tasks_file that is included in the blueprint’s directory.
• Executing a Fabric task by specifying its path in the current Python environment.
• Executing a script by specifying the script’s path or URL.

Running Commands

In the following code, the run_commands plugin task is used and a list of commands is specified to be executed on the agent host.

  
imports:
    - http://www.getcloudify.org/spec/fabric-plugin/1.3/plugin.yaml

node_templates:
  example_node:
    type: cloudify.nodes.WebServer
    interfaces:
      cloudify.interfaces.lifecycle:
          start:
            implementation: fabric.fabric_plugin.tasks.run_commands
            inputs:
              commands:
                - echo "source ~/myfile" >> ~/.bashrc
                - apt-get install -y python-dev git
                - pip install my_module
  

Running Tasks

In the following code, the tasks file path relative to the blueprint’s directory is specified, together with the task’s name in that file and (optional) task properties that will be used when the task is called.

  
imports:
    - http://www.getcloudify.org/spec/fabric-plugin/1.3/plugin.yaml

node_templates:
  example_node:
    type: cloudify.nodes.WebServer
    interfaces:
      cloudify.interfaces.lifecycle:
        start:
          implementation: fabric.fabric_plugin.tasks.run_task
          inputs:
            tasks_file: my_tasks/tasks.py
            task_name: install_nginx
            task_properties:
              important_prop1: very_important
              important_prop2: 300
  

Example

  
#my_tasks/tasks.py
from fabric.api import run, put
from cloudify import ctx

def install_nginx(important_prop1, important_prop2):
    ctx.logger.info('Installing nginx. Some important props:'
                    ' prop1: {0}, prop2: {1}'
                    .format(important_prop1, important_prop2))
    run('sudo apt-get install nginx')


def configure_nginx(config_file_path):
    # configure the webserver to run with our premade configuration file.
    conf_file = ctx.download_resource(config_file_path)
    put(conf_file, '/etc/nginx/conf.d/')


def start_nginx(ctx):
    run('sudo service nginx restart')
  

Running Module Tasks

This example is similar to the previous one, with the exception that, if the Fabric task that you want to execute is already installed in the Python environment in which the operation will run, you can specify the Python path to the function.

  
imports:
    - http://www.getcloudify.org/spec/fabric-plugin/1.3/plugin.yaml

node_templates:
  example_node:
    type: cloudify.nodes.WebServer
    interfaces:
      cloudify.interfaces.lifecycle:
        start:
          implementation: fabric.fabric_plugin.tasks.run_module_task
          inputs:
            task_mapping: some_package.some_module.install_nginx
            task_properties:
              important_prop1: very_important
              important_prop2: 300
  

Running Scripts

The Fabric plugin can execute scripts remotely and provides access to the ctx API for interacting with Cloudify in the same manner as with the script plugin.

Example:

  
node_templates:
  example_node:
    type: cloudify.nodes.WebServer
    interfaces:
      cloudify.interfaces.lifecycle:
        start:
          implementation: fabric.fabric_plugin.tasks.run_script
          inputs:
            # Path to the script relative to the blueprint directory
            script_path: scripts/start.sh
            MY_ENV_VAR: some-value
  

Operation Inputs

Operation inputs passed to the run_script task are available as environment variables in the script’s execution environment. Complex data structures such as dictionaries and lists are JSON-encoded when exported as environment variables.

Process Configuration

The run_script task accepts a process input that enables the process that runs the script to be configured:

• cwd - The working directory to use when running the script.
• args - List of arguments to pass to the script.
• command_prefix - The command prefix to use when running the script. This is not necessary if the script contains the #! line.
• env - Dictionary of environment variables to be incorporated into the script’s process.

Example:

  
node_templates:
  example_node:
    type: cloudify.nodes.WebServer
    interfaces:
      cloudify.interfaces.lifecycle:
        start:
          implementation: fabric.fabric_plugin.tasks.run_script
          inputs:
            script_path: scripts/start.sh
            # Optional
            process:
              # Optional
              cwd: /home/ubuntu
              # Optional
              command_prefix:
              # Optional
              args: [--arg1, --arg2, arg3]
              # Optional
              env:
                MY_VAR_1: my_value_1
                MY_VAR_2: my_value_2
  

Executing Commands or Scripts with sudo Privileges

The run_commands and run_script execution methods both accept a use_sudo input (which defaults to false). When true, the commands or script are executed using sudo. This enables, for instance, the use of the sudo_prefix Fabric env property to run an alternative implementation of sudo. See additional sudo-related configuration that you can apply to your Fabric env here.

Following is an example that uses use_sudo and sudo_prefix:

  
imports:
    - http://www.getcloudify.org/spec/fabric-plugin/1.3/plugin.yaml

node_templates:
  example_node:
    type: cloudify.nodes.WebServer
    interfaces:
      cloudify.interfaces.lifecycle:
          create:
            implementation: fabric.fabric_plugin.tasks.run_commands
            inputs:
              commands:
                - apt-get install -y python-dev git
                - echo 'config' > /etc/my_config
              # if `use_sudo` is omitted, it defaults to `false`
              use_sudo: true
              fabric_env:
                host_string: 10.10.1.10
                user: some_username
                password: some_password
                sudo_prefix: 'mysudo -c'
  

Hiding Output

Fabric generates output of its command execution. You can hide some of that output, for example to make your execution logs more readable, or to ignore irrelevant data. To hide output, use the hide_output input with any of the four execution methods. The hide_output input is a list of groups of outputs to hide as specified here.

An example that uses hide_output:

  
imports:
    - http://www.getcloudify.org/spec/fabric-plugin/1.3/plugin.yaml

node_templates:
  example_node:
    type: cloudify.nodes.WebServer
    interfaces:
      cloudify.interfaces.lifecycle:
        start:
          implementation: fabric.fabric_plugin.tasks.run_script
          inputs:
            # Path to the script relative to the blueprint directory
            script_path: scripts/start.sh
            MY_ENV_VAR: some-value
            # If omitted, nothing will be hidden
            hide_output:
              - running
              - warnings
  

SSH Configuration

The Fabric plugin extracts the correct host IP address based on the node’s host. It also uses the username and key file path if they were set globally during the bootstrap process. However, you can override these values and additional SSH configuration by passing fabric_env to operation inputs. This applies to run_commands, run_task and run_module_task. The fabric_env input is passed as-is to the underlying Fabric library. Check their documentation for additional details.

Following is an example that uses fabric_env:

  
imports:
    - http://www.getcloudify.org/spec/fabric-plugin/1.3/plugin.yaml

node_templates:
  example_node:
    type: cloudify.nodes.WebServer
    interfaces:
      cloudify.interfaces.lifecycle:
        start:
          implementation: fabric.fabric_plugin.tasks.run_commands
          inputs:
            commands: [touch ~/my_file]
            fabric_env:
              host_string: 192.168.10.13
              user: some_username
              key_filename: /path/to/key/file
  

ctx for the Fabric Plugin

Starting with Cloudify 3.4 and fabric-plugin 1.4, Cloudify now supports using ctx in Python scripts executed by the fabric plugin on remote machines. Most of the functionality is similiar to how the script plugin exposes the ctx object.

Executing ctx Commands

Until now, to use the Fabric plugin to execute Python scripts you had to use ctx commands in the following way.

  
os.system('ctx logger info Hello!')
  

Now, you can do one of two things to achieve the same result:

  
from cloudify import ctx

ctx.logger.info("Hello!")
  

or

  
from cloudify import ctx

ctx('logger info Hello!')
  

The first example shows native ctx usage that can be used to perform most of the trivial actions you can perform using the script plugin. For example, using the logger; retrieving runtime properties and setting them for node instances; setting the source/target node instances runtime properties in relationship operations; retrieving node properties; downloading blueprint resources; aborting operations, and so on.

The second example demonstrates that you can still use ctx to execute commands as if you are running it from a bash script.

The most notable difference is that, to get all properties for a node or runtime properties for a node instance, you have to run the following:

  
from cloudify import ctx

my_node_properties = ctx.node.properties.get_all()
my_instance_runtime_properties = ctx.instance.runtime_properties.get_all()
  

This is also true for source and target node properties and node instance runtime properties.