Bootstrap Chef nodes to connect them to the Chef server

A Chef node is a physical or virtual machine with an operating system that is connected to the Chef server. Once the node has made the connection to the Chef server, the installed Chef Client can execute Chef cookbooks to configure the machine.

Bootstrapping is the process to connect the node the first time to the Chef server, or to attach it again if the node lost the connectivity to the Chef server. To be able to bootstrap a node, your workstation needs to have the Chef Development Kit installed. The kit includes the ‘knife’ command that communicates with the Chef server. Your workstation also has to be able to connect to the Chef server with the YOUR_USERNAME.pem file you store in the .chef directory just above your cookbooks.

Bootstrap a Linux node

To bootstrap a Linux node, open a terminal window on your workstation and execute the command:

With password authentication
-----------------------------
knife bootstrap MY_NODE_IP -x SERVER_ADMIN_USERNAME -P SERVER_ADMIN_PASSWORD --sudo --node-name THE_NODE_NAME --environment THE_ENVIRONMENT --run-list 'recipe[MY_COOKBOOK1::default],recipe[MY_COOKBOOK2::default]' --json-attributes '{"MY_ATTRIB1":"MY_VALUE1","MY_ATTRIB2":"MY_VALUE2"}'

With key authentication
-----------------------
knife bootstrap MY_NODE_IP -x SERVER_ADMIN_USERNAME -i PATH_TO_KEY_FILE --sudo --node-name THE_NODE_NAME --environment THE_ENVIRONMENT --run-list 'recipe[MY_COOKBOOK1::default],recipe[MY_COOKBOOK2::default]' --json-attributes '{"MY_ATTRIB1":"MY_VALUE1","MY_ATTRIB2":"MY_VALUE2"}'

Bootstrap a Windows node

knife bootstrap windows winrm MY_NODE_IP -x SERVER_ADMIN_USERNAME -P SERVER_ADMIN_PASSWORD --node-name THE_NODE_NAME --environment THE_ENVIRONMENT --run-list 'recipe[MY_COOKBOOK1::default],recipe[MY_COOKBOOK2::default]' --json-attributes '{"MY_ATTRIB1":"MY_VALUE1","MY_ATTRIB2":"MY_VALUE2"}' -V

where

  • MY_NODE_IP is the IP address of the node you want to attach to the Chef server,
  • SERVER_ADMIN_USERNAME and SERVER_ADMIN_PASSWORD are the credentials to connect to the node.
    If the Windows server is in the Windows domain start the username with the domain name MY_DOMAIN\\SERVER_ADMIN_USERNAME
    If the Windows server is not in the domain start the username with the IP address MY_NODE_IP\\SERVER_ADMIN_USERNAME
  • THE_NODE_NAME is the unique name you want the node to use in the Chef server database. If you are bootstrapping a server that lost connectivity to the Chef server or moving the node to another Chef server, find the node name in the node list.
  • THE_ENVIRONMENT is the name of the environment the node will run the cookbook in,
  • The run list is a list of cookbooks and roles. No spaces are allowed in the string.

Troubleshooting

If the known_hosts file already contains an entry for a different server with the same IP address, we get the error message

ERROR: Net::SSH::HostKeyMismatch: fingerprint … does not match for “…”

Open the ~/.ssh/known_hosts file and delete the line that contains the IP address of the server.

Dynamically set Chef resource attributes

When you need to set a Chef resource attribute based on the current state of the environment, there is a way to dynamically provide the value.

  1. Set the value of a boolean variable with a test,
  2. Declare the Chef resource and assign a reference to it to a variable,
  3. Set the resource attribute based on the value of the boolean variable.
# Set a boolean variable with a test 
def MY_BOOLEAN_VARIABLE?
  "#{node['domain']}" != ""
end 

# Execute a resource and get a reference to it into a variable
t = MY_RESOURCE 'MY_RESOURCE_NAME' do
  ...
end
# Set the attribute value based on the boolean variable
t.MY_RESOURCE_ATTRIBUTE MY_ATTRIBUTE_VALUE if MY_BOOLEAN_VARIABLE?

 

 

How to create a bootable USB drive to install Windows

If the computer you want to install Microsoft WIndows on, does not have a DVD drive, you can install Windows from a USB drive. To start the computer from the USB drive, you need to prepare the drive to make it bootable.

Microsoft has a free tool that can download the edition of the Windows operating system you need, format the USB drive, make it bootable, and place the installer file on it.

  1. Using a web browser navigate to https://www.microsoft.com/en-us/software-download/windows10,
  2. Click the Download tool now button to install the Microsoft Media Creation Tool,
  3. Start the downloaded MediaCreationTool.exe program and follow the prompts.

Setup failed: Failed to copy slug dir: lstat /Users: no such file or directory error in Terraform Enterprise

When you try to execute a Terraform configuration in Terraform Enterprise (Atlas) you may get the error message:

Setup failed: Failed to copy slug dir: lstat /Users: no such file or directory

Cause:

The Git repository contains the .terraform/modules directory, and the Terraform Enterprise server cannot get the latest modules from GitHub.

Solution:

  1. Create a .gitignore file in the repository and add these lines: 
    */.terraform/modules/

# Ignore DS_Store if working on a mac
.DS_Store
  2. Delete the .terraform directory and push the changes to GitHub

 

 

Install a Python package

To install a Python package on Macintosh

  1. Download the Python package to your workstation,
  2. Unpack the package,
  3. Open a terminal window,
  4. Start sudo, 
    sudo -i
  5. Change to the directory of the package,
  6. Install the package. 
    pip install PACKAGE_NAME

If you don’t install the package in sudo mode, you will get “Permission denied” errors during the package installation.

Troubleshooting

When you encounter the warning message

WARNING: The directory ‘/Users/…/Library/Caches/pip’ or its parent directory is not owned or is not writable by the current user. The cache has been disabled. Check the permissions and owner of that directory. If executing pip with sudo, you should use sudo’s -H flag.

To make yourself the owner of the /Users/…/Library/Caches/pip directory execute

sudo chown -R $(whoami) ~/Library/Caches/pip

PyCharm configuration

When you install PyCharm, the default Python interpreter is may not the version you want to use for your new projects. When you create a new project, and the project interpreter is not set, you may get the following error message:

Executed command:
/var/folders/_x/_f0zzs1s4sx6bk4s8n78l2jsbn9r3z/T/tmpBoQLx_pycharm-management/pip-9.0.1/setup.py install

Error occurred:
40:357: execution error: /System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/distutils/dist.py:266: UserWarning: Unknown distribution option: ‘python_requires’

Command output:
40:357: execution error: /System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/distutils/dist.py:266: UserWarning: Unknown distribution option: ‘python_requires’
warnings.warn(msg)
warning: build_py: byte-compiling is disabled, skipping.
warning: install_lib: byte-compiling is disabled, skipping.
error: byte-compiling is disabled.
(1)

Solution:

Set the default Python interpreter to the latest installed version before you create your project:

  1. Start PyCharm
  2. In the File menu select Default Settings…
  3. On the left side select Project Interpreter,
  4. On the right side click the arrow of the Project Interpreter drop-down
  5. Select the Python interpreter you want to use by default, and click the OK button.

Python ImportError: No module named …

Symptom:

from MY_FOLDER.MY_FILE import MY_CLASS causes an error:
ImportError: No module named MY_FOLDER.MY_FILE

Debugging:

  1. Execute the program in debug mode,
  2. In the Variables window expand Special Variables,
  3. Read the __warningregistry__ value.

Possible cause:

The __init__.py file is missing in the directory of the referenced class.

Solution:

Create an empty __init__.py file in the directory where the class is referenced from.

Python basics

Great Python introductory video for C# developers
https://www.youtube.com/watch?v=jj60geqaP08

__  (double underscore) Starting the attribute name with double underscore attribute makes it private. To expose the private attributes and methods

print(dir(MY_CLASS))

 

Code hierarchy

In Python indentation denotes the hierarchy of the instructions, not curly braces, like in C# or Java.

Directories

When you create a directory in your project, create an empty __init__.py file in the new directory to be able to reference objects from that directory, and avoid

from MY_FOLDER.MY_FILE import MY_CLASS causes an error:
ImportError: No module named MY_FOLDER.MY_FILE

Classes

Predefined methods

__init__(self)  Initializer method (constructor)

__repr__(self)  Representation

__iter__(self)  Method to define hot to iterate through the object

Decorators

@property  Exposes a method as a property of the class

from _04_anonymous.anonobject import AnonObject
ImportError: No module named _04_anonymous.anonobject

{(“Not importing directory ‘/Users/pinterl/Git/devops-scripts/Python_Tutorial/Python/Python_for_C_sharp_developers/_04_anonymous’: missing __init__.py”, <type ‘exceptions.ImportWarning’>, 6): True}

Working with PyCharm

Project management

Create a new project in PyCharm

  1. In the File menu select New Project…,
  2. On the left side select the Python framework you want to use,
  3. Enter the name for your project to the end of the Location path,
  4. If you have selected a framework that asks for more information
    1. Click the More Settings link and enter the additional values,
    2. Click the Create button,
    3. PyCharm generates folders for your project and application,
    4. When PyCharm asks you about compatibility inspection, enable it, to make sure your code is compatible with future versions of Python.
    5. PyCharm will enable Code compatibility inspection. Click OK to save the setting.
    6. PyCharm will still set your project interpreter to 2.6, so set it to 2.7. In the PyCharm menu select Preferences…,
    7. On the left side select Project:…, Project Interpreter,
    8. In the Project Interpreter drop-down select 2.7 and click the OK button.

Delete a project in PyCharm

The PyCharm project explorer does not have a delete option. To delete a PyCharm project

  1. Open the project location in Finder,
  2. Move the project folder to the Trash,
  3. The PyCharm project explorer window will reflect the change.

Shortcuts, tips, and tricks

 Auto generate

Auto generate functions, classes, attributes

  1. Enter the name of the undefined element where you want to use it,
  2. Click the light bulb, or press ⌥⏎ (Alt-Enter) to pop up the Intention Action alert,
  3. Select the action to generate the definition.

Auto generate fields for classes

  1. Enter the __init__ function of the class with the field names,
  2. Place the cursor on the field you want to generate the definition for,
  3. Click the light bulb, or press ⌥⏎ (Alt-Enter) to pop up the Intention Action alert,
  4. Select Add field ‘…’ to class …,
  5. Press Enter to select the option,
  6. Press Enter at the end of the new line to move the cursor to the next line, otherwise, the Intention Action alert does not pop up when you press ⌥⏎ (Alt-Enter)

 

Code completion

  • Press Ctrl-Space to complete the name of the element.
  • Press Ctrl-Space twice to complete the name of any class, even if it is not yet imported. The import statement will be automatically added.

Quick documentation

To get a short documentation on an element under the cursor, press F1. (By default on a Macintosh you need to press fn-F1, because the F1 button is programmed to adjust the brightness.)

For more information

Auto completing code, see https://www.jetbrains.com/help/pycharm/auto-completing-code.html

Keyboard shortcuts
https://www.jetbrains.com/help/pycharm/keyboard-shortcuts-and-mouse-reference.html