python-openstackclient/doc/source/contributor/humaninterfaceguide.rst

Human Interface Guide

Note: This page covers the OpenStackClient CLI only but looks familiar because it was derived from the Horizon HIG.

Overview

What is a HIG? The Human Interface Guidelines document was created for OpenStack developers in order to direct the creation of new OpenStackClient command interfaces.

Personas

Personas are archetypal users of the system. Keep these types of users in mind when designing the interface.

Alice the admin

Alice is an administrator who is responsible for maintaining the OpenStack cloud installation. She has many years of experience with Linux systems administration.

Darren the deployer

Darren is responsible for doing the initial OpenStack deployment on the host machines.

Emile the end-user

Emile uses the cloud to do software development inside of the virtual machines. She uses the command-line tools because she finds it quicker than using the dashboard.

Principles

The principles established in this section define the high-level priorities to be used when designing and evaluating interactions for the OpenStack command line interface. Principles are broad in scope and can be considered the philosophical foundation for the OpenStack experience; while they may not describe the tactical implementation of design, they should be used when deciding between multiple courses of design.

A significant theme for designing for the OpenStack experience concerns focusing on common uses of the system rather than adding complexity to support functionality that is rarely used.

Consistency

Consistency between OpenStack experiences will ensure that the command line interface feels like a single experience instead of a jumble of disparate products. Fractured experiences only serve to undermine user expectations about how they should interact with the system, creating an unreliable user experience. To avoid this, each interaction and visual representation within the system must be used uniformly and predictably. The architecture and elements detailed in this document will provide a strong foundation for establishing a consistent experience.

Example Review Criteria

• Do the command actions adhere to a consistent application of actions?
• Has a new type of command subject or output been introduced?
• Does the design use command elements (options and arguments) as defined? (See Core Elements.)
• Can any newly proposed command elements (actions or subjects) be accomplished with existing elements?
• Does the design adhere to the structural model of the core experience? (See Core Architecture.)
• Are any data objects displayed or manipulated in a way contradictory to how they are handled elsewhere in the core experience?

Simplicity

To best support new users and create straight forward interactions, designs should be as simple as possible. When crafting new commands, designs should minimize the amount of noise present in output: large amounts of nonessential data, overabundance of possible actions and so on. Designs should focus on the intent of the command, requiring only the necessary components and either removing superfluous elements or making them accessible through optional arguments. An example of this principle occurs in OpenStack's use of tables: only the most often used columns are shown by default. Further data may be accessed through the output control options, allowing users to specify the types of data that they find useful in their day-to-day work.

Example Review Criteria

• Can options be used to combine otherwise similar commands?
• How many of the displayed elements are relevant to the majority of users?
• If multiple actions are required for the user to complete a task, is each step required or can the process be more efficient?

User-Centered Design

Commands should be design based on how a user will interact with the system and not how the system's backend is organized. While database structures and APIs may define what is possible, they often do not define good user experience; consider user goals and the way in which users will want to interact with their data, then design for these work flows and mold the interface to the user, not the user to the interface.

Commands should be discoverable via the interface itself.

To determine a list of available commands, use the -h or --help options:

$ openstack --help

For help with an individual command, use the help command:

$ openstack help server create

Example Review Criteria

• How quickly can a user figure out how to accomplish a given task?
• Has content been grouped and ordered according to usage relationships?
• Do work flows support user goals or add complexity?

Transparency

Make sure users understand the current state of their infrastructure and interactions. For example, users should be able to access information about the state of each machine/virtual machine easily, without having to actively seek out this information. Whenever the user initiates an action, make sure a confirmation is displayed[1] to show that an input has been received. Upon completion of a process, make sure the user is informed. Ensure that the user never questions the state of their environment.

[1] This goes against the common UNIX philosophy of only reporting error conditions and output that is specifically requested.

Example Review Criteria

• Does the user receive feedback when initiating a process?
• When a process is completed?
• Does the user have quick access to the state of their infrastructure?

Architecture

Command Structure

OpenStackClient has a consistent and predictable format for all of its commands.

• The top level command name is openstack
• Sub-commands take the form:

openstack [<global-options>] <object-1> <action> [<object-2>] [<command-arguments>]

Subcommands shall have three distinct parts to its commands (in order that they appear):

• global options
• command object(s) and action
• command options and arguments

Output formats:

• user-friendly tables with headers, etc
• machine-parsable delimited

Global Options

Global options are global in the sense that they apply to every command invocation regardless of action to be performed. They include authentication credentials and API version selection. Most global options have a corresponding environment variable that may also be used to set the value. If both are present, the command-line option takes priority. The environment variable names are derived from the option name by dropping the leading dashes ('--'), converting each embedded dash ('-') to an underscore ('_'), and converting to upper case.

• Global options shall always have a long option name, certain common options may also have short names. Short names should be reserved for global options to limit the potential for duplication and multiple meanings between commands given the limited set of available short names.
• All long options names shall begin with two dashes ('--') and use a single dash ('-') internally between words (--like-this). Underscores ('_') shall not be used in option names.
• Authentication options conform to the common CLI authentication guidelines in authentication.

For example, --os-username can be set from the environment via OS_USERNAME.

--help

The standard --help global option displays the documentation for invoking the program and a list of the available commands on standard output. All other options and commands are ignored when this is present. The traditional short form help option (-h) is also available.

--version

The standard --version option displays the name and version on standard output. All other options and commands are ignored when this is present.

Command Object(s) and Action

Commands consist of an object described by one or more words followed by an action. Commands that require two objects have the primary object ahead of the action and the secondary object after the action. Any positional arguments identifying the objects shall appear in the same order as the objects. In badly formed English it is expressed as "(Take) object1 (and perform) action (using) object2 (to it)."

<object-1> <action> [<object-2>]

Examples:

• group add user <group> <user>
• volume type list # Note that volume type is a two-word single object

The help command is unique as it appears in front of a normal command and displays the help text for that command rather than execute it.

Object names are always specified in command in their singular form. This is contrary to natural language use.

Command Arguments and Options

Each command may have its own set of options distinct from the global options. They follow the same style as the global options and always appear between the command and any positional arguments the command requires.

Command options shall only have long names. The small range of available short names makes it hard for a single short option name to have a consistent meaning across multiple commands.

Option Forms

• boolean: boolean options shall use a form of --<true>|--<false> (preferred) or --<option>|--no-<option>. For example, the enabled state of a project is set with --enable|--disable.

Command Output

The default command output is pretty-printed using the Python prettytable module.

Machine-parsable output format may be specified with the --format option to list and show commands. list commands have an option (--format csv) for CSV output and show commands have an option (--format shell) for the shell variable assignment syntax of var="value". In both cases, all data fields are quoted with "

Help Commands

The help system is considered separately due to its special status among the commands. Rather than performing tasks against a system, it provides information about the commands available to perform those tasks. The format of the help command therefore varies from the form for other commands in that the help command appears in front of the first object in the command.

The options --help and -h display the global options and a list of the supported commands. Note that the commands shown depend on the API versions that are in effect; i.e. if --os-identity-api-version=3 is present Identity API v3 commands are shown.

Examples

The following examples depict common command and output formats expected to be produces by the OpenStack client.

Authentication

Using global options:

$ openstack --os-tenant-name ExampleCo --os-username demo --os-password secret --os-auth-url http://localhost:5000:/v2.0 server show appweb01
+------------------------+-----------------------------------------------------+
|        Property        |                Value                                |
+------------------------+-----------------------------------------------------+
| OS-DCF:diskConfig      | MANUAL                                              |
| OS-EXT-STS:power_state | 1                                                   |
| flavor                 | m1.small                                            |
| id                     | dcbc2185-ba17-4f81-95a9-c3fae9b2b042                |
| image                  | Ubuntu 12.04 (754c231e-ade2-458c-9f91-c8df107ff7ef) |
| keyname                | demo-key                                            |
| name                   | appweb01                                            |
| private_address        | 10.4.128.13                                         |
| status                 | ACTIVE                                              |
| user                   | demo                                                |
+------------------------+-----------------------------------------------------+

Using environment variables:

$ export OS_TENANT_NAME=ExampleCo
$ export OS_USERNAME=demo
$ export OS_PASSWORD=secret
$ export OS_AUTH_URL=http://localhost:5000:/v2.0
$ openstack server show appweb01
+------------------------+-----------------------------------------------------+
|        Property        |                Value                                |
+------------------------+-----------------------------------------------------+
| OS-DCF:diskConfig      | MANUAL                                              |
| OS-EXT-STS:power_state | 1                                                   |
| flavor                 | m1.small                                            |
| id                     | dcbc2185-ba17-4f81-95a9-c3fae9b2b042                |
| image                  | Ubuntu 12.04 (754c231e-ade2-458c-9f91-c8df107ff7ef) |
| keyname                | demo-key                                            |
| name                   | appweb01                                            |
| private_address        | 10.4.128.13                                         |
| status                 | ACTIVE                                              |
| user                   | demo                                                |
+------------------------+-----------------------------------------------------+

Machine Output Format

Using the csv output format with a list command:

$ openstack server list --format csv
"ID","Name","Status","Private_Address"
"ead97d84-6988-47fc-9637-3564fc36bc4b","appweb01","ACTIVE","10.4.128.13"

Using the show command options of shell output format and adding a prefix of my_ to avoid collisions with existing environment variables:

$ openstack server show --format shell --prefix my_ appweb01
my_OS-DCF:diskConfig="MANUAL"
my_OS-EXT-STS:power_state="1"
my_flavor="m1.small"
my_id="dcbc2185-ba17-4f81-95a9-c3fae9b2b042"
my_image="Ubuntu 12.04 (754c231e-ade2-458c-9f91-c8df107ff7ef)"
my_keyname="demo-key"
my_name="appweb01"
my_private_address="10.4.128.13"
my_status="ACTIVE"
my_user="demo"