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Script Plugin

The Script plugin can be used to map node life-cycle operations and workflows to scripts that are included in your blueprint. Scripts can be written in Python, bash, ruby, and so on.

The Script plugin is pre-installed with the default agent packages and is defined in types.yaml. The source code can be found at https://github.com/cloudify-cosmo/cloudify-common

Plugin Requirements:

Usage

Following are usage examples that demonstrate different configuration options.

Basic Usage

blueprint.yaml 

imports:
  - http://www.getcloudify.org/spec/cloudify/5.0.0/types.yaml

node_templates:
  example_web_server:
    # The web server type is only used for this example. The type used
    # could be any valid cloudify type.
    type: cloudify.nodes.WebServer
    interfaces:
      cloudify.interfaces.lifecycle:
        start: scripts/start.sh

scripts/start.sh 

#! /bin/bash -e
ctx logger info "Hello to this world"

Description

Notice that the cloudify.interface.lifecycle.start operation is mapped directly to a script. When an operation is mapped, if the mapping points to a resource that is included in the blueprint directory, it is considered to be a script and the Script plugin is used. This means that the above mapping is equivalent to: 

interfaces:
  cloudify.interfaces.lifecycle:
    start:
      implementation: script.script_runner.tasks.run
      inputs:
        script_path: scripts/start.sh

Short Example Script Description

The first line 

#! /bin/bash -e

makes the script run with /bin/bash. Had the script been written using ruby, for example, it would point to /bin/ruby.

The second line 

ctx logger info "Hello to this world"

demonstrates how scripts can access the operation context. The line is equivalent to writing 

ctx.logger.info('Hello to this world')

within a python plugin operation.

A more detailed description about accessing the operation context is provided later in this topic.

Process Configuration

The following example demostrates how you can configure the working directory in which the script is executed, pass arguments to the script and update environment variables of the script process.

blueprint.yaml 

imports:
  - http://www.getcloudify.org/spec/cloudify/5.0.0/types.yaml

node_templates:
  example_web_server:
    type: cloudify.nodes.WebServer
    interfaces:
      cloudify.interfaces.lifecycle:
        start:
          implementation: scripts/start.sh
          inputs:
            process:
              # this directory should already exist
              cwd: /tmp/workdir
              args: [arg1_value, arg2_value]
              env:
                MY_ENV_VARIABLE: MY_ENV_VARIABLE_VALUE

scripts/start.sh 

#! /bin/bash -e

# will log "current working directory is: /tmp/workdir"
ctx logger info "current working directory is: ${PWD}"

# will log "first arg is: arg1_value"
ctx logger info "first arg is: $1"

# will log "my env variable is: MY_ENV_VARIABLE_VALUE"
ctx logger info "my env variable is: ${MY_ENV_VARIABLE}"

Script Location

The script location may be any of the following:

Python Scripts

Python scripts receive specific treatment in the Script plugin. If the script path ends with a .py extension, it is evaluated within the plugin operation. This provides a simple way to access the full plugin API ,without having to write an entire plugin.

Example

blueprint.yaml 

imports:
  - http://www.getcloudify.org/spec/cloudify/5.0.0/types.yaml

node_templates:
  example_web_server:
    type: cloudify.nodes.WebServer
    properties:
      port: 8080
    interfaces:
      cloudify.interfaces.lifecycle:
        start: scripts/start.py

scripts/start.py 

from cloudify import ctx

ctx.logger.info('Just logging the web server port: {0}'
                .format(ctx.node.properties['port']))

Operation Inputs

You can import ctx_parameters from cloudify.state, to access operation inputs in a Python script.

Assuming a port operation input was passed, you can access it as follows:

from cloudify import ctx
from cloudify.state import ctx_parameters as inputs

ctx.logger.info('The port operation input is : {0}'
                .format(inputs['port']))

Eval Python

To evaluate a script as Python that does not have a .py extension, you can explicity specify this requirement using the eval_python process configuration.

interfaces:
  cloudify.interfaces.lifecycle:
    start:
      implementation: script/my_python_script
      inputs:
        process:
          eval_python: true

If a script does have a .py extension and you want it to be executed in an external process, pass false to the eval_python process configuration. Note that accessing the operation context in this case processed via the context proxy, as with any other none Python script.

Command Prefix

In some cases, you might not want to use #! to specify how to execute the script (or cannot, in the event that you are running the script on Windows). In this case, you can use the command_prefix process configuration as follows

blueprint.yaml 

imports:
  - http://www.getcloudify.org/spec/cloudify/5.0.0/types.yaml

node_templates:
  example_web_server:
    type: cloudify.nodes.WebServer
    interfaces:
      cloudify.interfaces.lifecycle:
        start:
          implementation: scripts/start.rb
          inputs:
            process:
              command_prefix: /opt/ruby/bin/ruby

This executes start.rb with the ruby binary in /opt/ruby/bin/ruby.

Windows PowerShell scripts

Windows PowerShell scripts receive specific treatment in the Script plugin. If the script path ends with a .ps1 extension, it is automatically executed as if command_prefix was already set to powershell This can be achieved as follows:

blueprint.yaml 

imports:
  - http://www.getcloudify.org/spec/cloudify/5.0.0/types.yaml

node_templates:
  example_web_server:
    type: cloudify.nodes.WebServer
    interfaces:
      cloudify.interfaces.lifecycle:
        start: scripts/start.ps1

This executes start.ps1 using the PowerShell console application in the script’s execution environment.

Running PowerShell in 64-bit mode

The Windows agent runs as a 32-bit service. If PowerShell scripts are invoked, they will be invoked in a 32-bit PowerShell process.

In order to run PowerShell in 64-bit mode, you will have to add the command_prefix input as follows:

implementation: scripts/start.ps1
inputs:
  process:
    command_prefix: C:\Windows\sysnative\WindowsPowerShell\v1.0\PowerShell.exe

(sysnative will be automatically resolved to the 32-bit Windows system libraries when used in a 32-bit process)

Hello World Example

For a more complete usage example, see the Hello World example.

Operation Inputs

The Script plugin supports passing node template operation inputs as environment variables that are available in the script’s execution environment. Complex data structures such as dictionaries and lists will be JSON-encoded when exported as environment variables.

In the following example, the port input set for the start operation will be available as a port environment variable within the start.sh script:

blueprint.yaml 

imports:
  - http://www.getcloudify.org/spec/cloudify/5.0.0/types.yaml

node_templates:
  example_web_server:
    type: cloudify.nodes.WebServer
    interfaces:
      cloudify.interfaces.lifecycle:
        start:
          implementation: scripts/start.sh
          # start operation inputs
          inputs:
            port: 8080

scripts/start.sh 

echo "Starting web server..."
nohup python -m SimpleHTTPServer ${port} > /dev/null 2>&1 &

Process Configuration Options

Option Value Type Description
cwd string Sets the current working directory for the script process.
env dictionary Adds environment variables to the script process.
args list Command-line arguments to pass to the script (as $1, $2 etc. on Linux, or %1, %2 etc. on Windows).
command_prefix string A prefix to add before the script’s path. This can be used to specify an interpreter, as well as instead of a shebang line (such as #!/bin/bash) on Linux.
log_stdout boolean If true (the default), the script’s standard output stream is automatically logged to Cloudify’s logger.
log_stderr boolean If true (the default), the script’s standard error stream is automatically logged to Cloudify’s logger.
stderr_to_stdout boolean If true, then the script’s standard error stream is redirected to the output stream. The default is false.
eval_python boolean Denoting whether the script should be evaluated as Python code in-line (true), or executed as an external process (false).
ctx_proxy_type string The context proxy type (none, unix, tcp or http).

Workflow Scripts

You can use the Script plugin to execute workflow scripts.

For example, to add a custom workflow that runs a custom operation on each node, write a simple blueprint with two nodes, as follows:

blueprint.yaml 

imports:
  - http://www.getcloudify.org/spec/cloudify/5.0.0/types.yaml

node_templates:
  node1:
    type: cloudify.nodes.Root
    interfaces:
      custom:
        touch: scripts/touch.py
  node2:
    type: cloudify.nodes.Root
    interfaces:
      custom:
        touch: scripts/touch.py

workflows:
  touch_all:
    mapping: workflows/touch_all.py
    parameters:
      touched_value:
        description: the value to touch the instance with

You could then write a touch.py script. Note that this script ends with a .py extension, so it will be evaluated as Python code.

scripts/touch.py 

from cloudify import ctx
from cloudify.state import ctx_parameters as p

ctx.instance.runtime_properties['touched'] = p.touched_value

The script will update the touched runtime property of the current node instance with an expected touched_value property that will be injected by the workflow executing the operation.

Then you can write the actual workflow.

workflows/touch_all.py 

from cloudify.workflows import ctx
from cloudify.workflows import parameters as p

for node in ctx.nodes:
    for instance in node.instances:
        instance.execute_operation('custom.touch', kwargs={
            'touched_value': p.touched_value
        })

Having written the workflow, you can now execute it: 

cfy executions start -w touch_all -d my_deployment --parameters '{"touched_value": "my_value"}'

All the node instances now have their touched runtime property set to my_value.

Context Proxy

In the previous examples, ctx was referenced several times from within the scripts. This mechanism provides the means for accessing the ctx object in the manner in which it is usually accessed when writing plugins.

Following is a description of how calls to the ctx executable, translate to the ctx object access.

Attribute access

#! /bin/bash
ctx bootstrap-context cloudify-agent agent-key-path
Translates to 
ctx.bootstrap_context.cloudify_agent.agent_key_path

In addition, note in this example that - in attributes (as an argument) is replaced with _.

Simple Method Invocation

#! /bin/bash
ctx logger info "Some logging"
Translates to 
ctx.logger.info('Some logging')

In the immediately above example, a logger attribute is searched on the ctx object. After being found, an info attribute is searched on the logger result. After that is found, it discovers that info is callable, so it invokes it with the remaining arguments.

Method Invocation with kwargs

#! /bin/bash
ctx download-resource images/hello.png '@{"target_path": "/tmp/hello.png"}'
Translates to 
ctx.download_resource('images/hello.png', **{'target_path': '/tmp/hello.png'})

In the above example, note that the final argument starts with @. This is further explained later in this topic. For now, this means that the argument will be parsed as json.

Note that the last argument is a dictionary, as the above demonstrates. If the last argument of a method invocation is a dictionary, it is treated as kwargs to the method invocation.

Dictionary Access

#! /bin/bash
# read access
ctx node properties application_name
ctx target instance runtime-properties username
ctx instance runtime-properties endpoint.port
ctx instance runtime-properties endpoint.urls[2]

# write access
ctx instance runtime-properties my_property my_value
ctx instance runtime-properties my_properties.my_nested_property nested_value
Translates to 
ctx.node.properties['application_name']
ctx.target.instance.runtime_properties['username']
ctx.instance.runtime_properties['endpoint']['port']
ctx.instance.runtime_properties['endpoint']['urls'][2]

ctx.instance.runtime_properties['my_property'] = 'my_value'
ctx.instance.runtime_properties['my_properties']['my_nested_property'] = 'nested_value'

Once a dictionary attribute is discovered during the attribute search, the following logic applies:

Non-String Arguments

To pass arguments that are not strings, for example when setting a runtime property to a number, you can prefix the argument with @ so that it is json-parsed before being evaluated.

#! /bin/bash
ctx instance runtime-properties number_of_clients @14
Translates to 
ctx.instance.runtime_properties['number_of_clients'] = 14  # instead of = '14'

Returning a Value

You can use ctx returns some_value to have the operation to return a value. This invocation sets some_value on the current ctx, and the Script plugin returns the value when the script terminates.

Note that this call does not make the script terminate, however it is best practice to make this call at the end of the script.

Command-Line Optional Arguments of ctx

The following flags must appear before the positional arguments.

Context Proxy Protocol

To call the ctx executable, you invoke the CLI client that is pre-installed with the plugin. When the Script plugin executes your script, it also starts a ctx proxy server that delegates calls to the actual ctx object instance.

Before the Script plugin starts the proxy server, it checks the following:

This behavior can be overridden by setting proxy_ctx_type of the process configuration to be one of unix, tcp, http or none. If none is set, no proxy server will be started.

The ctx CLI client implements a simple protocol on top of the above transport layers that can be implemented in other languages to provide a more streamlined access to the context.

When the Script plugin executes the script, it updates the script process with the CTX_SOCKET_URL environment variable.

The first two are valid ZeroMQ socket URLs and should be passed as is to the ZeroMQ client. The last one is the HTTP endpoint that should be used when making REST calls.

If a ZeroMQ client is implemented, it should start a request-based socket (as the proxy server starts the matching response socket).

If an HTTP client is implemented, it should make POST requests to the socket URL endpoint.

In all the protocols, the format of the request body is a json with the following structure: 

{
    "args": [...]
}
Where args is the list of arguments. So, for example, the arguments for ctx.properties['port'] is ["properties", "port"]

The format of the response body is a json with the following structure.

In the case of a successful execution: 

{
   "type": "result",
   "payload": RESULT_BODY
}
In the case of a failed execution: 
{
   "type": "error",
   "payload": {
      "type": ERROR_TYPE,
      "message": ERROR_MESSAGE,
      "traceback": ERROR_TRACEBACK
   }
}

See the CLI implementation for reference.

Troubleshooting

nohup

When you use nohup in your scripts, you must redirect the output and stderr to /dev/null and to run the operation in the background using &. For example: 

nohup python -m SimpleHTTPServer > /dev/null 2>&1 &

File Not Found Error

Different Linux distributions use different default interpreters. One might use bash, while the other uses sh. While bash will normally return an informative message in regards to the shebang line, the sh message might look something like this: 

/bin/sh: 1: <tmp_path>/...<script_name>: not found
This basically means that the specified path in the shebang line is invalid (which could be due to a syntax error or because the specified path does not lead anywhere).