Naming Conventions

This topic document serves to provide guidance on how to name resources in OpenStack public REST APIs so that our APIs feel consistent and professional.

REST API resource names

  • A resource in a REST API is always represented as the plural of an entity that is exposed by the API.

  • Resource names exposed in a REST API should use all lowercase characters.

  • Resource names may include hyphens.

  • Resource names should not include underscores or other punctuation (sole exception is the hyphen).

Fields in an API request or response body

HTTP requests against an API may contain a body which is typically a serialized representation of the resource that the user wished to create or modify. Similarly, HTTP responses contain a body that is usually the serialized representation of a resource that was created, modified, or listed by the server.

Fields within these serialized request and response bodies should be named according to these guidelines:

  • Field names should use the snake_case style, not CamelCase or StUdLyCaPs style.

Boolean fields

Boolean fields should be named so that the name completes the phrase “This is _____” or “This has ____”. For example, if you need a field to indicate whether the item in question is enabled, then “enabled” would be the proper form, as opposed to something like “is_enabled”. Similarly, to indicate a network that uses DHCP, the field name “dhcp_enabled” should be used, rather than forms such as “enable_dhcp” or just “dhcp”.

It is also strongly recommended that negative naming be avoided, so use ‘enabled’ instead of ‘disabled’ or ‘not_enabled’. The reason for this is that it is difficult to understand double negatives when reading code. In this case, “not_enabled = False” is harder to understand than “enabled = True”.

Boolean parameters

There are two types of boolean parameters: those that are used to supply the value for a boolean field as described above, and those that are used to influence the behavior of the called method. In the first case, the name of the parameter should match the name of the field. For example, if you are supplying data to populate a field named ‘enabled’, the parameter name should also be ‘enabled’. In the second case, though, where the parameter is used to toggle the behavior of the called method, the name should be more verb-like. A example of this form is the parameter “force”, which is commonly used to indicate that the method should carry out its action without the normal safety checks. And as with boolean fields, the use of negative naming for boolean parameters is strongly discouraged, for the same reasons.

State vs. Status

While these two names mean nearly the same thing, there are differences. In general, ‘state’ should be used when recording where in a series of steps a process is in. In other words, ‘state’ is expected to change, and then only to a small number of subsequent states. An example of this would be the building of a VM, which follows a series of steps, and either moves forward to the next state, or falls into an ERROR state.

Status, on the other hand, should be used for cases where there is no expectation of a series of changes. A service may have the status of “up” or “active”, and it is expected that it should remain like that unless either and admin changes it, or a failure occurs.