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DEPRECATION.md

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Deprecations in Vector

This document covers Vector's deprecation policy and process.

In the course of Vector's development it can be necessary to deprecate configuration and (rarely) features to keep Vector maintainable and its configuration interface consistent for users. To avoid breaking compatibility abruptly, we follow the following deprecation policy.

Policy

Vector will retain deprecated configuration or features for at least one minor version (this will transition to one major version when Vector hits 1.0).

This means that deprecations will be eligible for removal in the next minor release after they are announced; however, we will typically aim to support deprecations for a longer time period depending on their development maintenance burden. For example, a deprecation announced in v0.16.0 would be eligible to be removed in v0.17.0 but may be removed later in v0.20.0.

Exceptions can be made for deprecations related to security issues or critical bugs. These may result in removals being introduced in a release without being announced in a prior release.

Examples

Examples of possible deprecations in Vector:

  • Removal or rename of a configuration option
  • Removal or rename of a metric
  • Removal of a feature

Lifecycle of a deprecation

A deprecation goes through three stages: Deprecation, Migration, and Removal. These are described below.

Deprecation

A configuration option or feature in Vector is marked as deprecated.

When this happens, we will notify by:

  • Listing the deprecation in the Deprecations section of the upgrade guide for the release the deprecation was introduced in. This will include instructions on how to transition if applicable.
  • Adding a deprecation note to the documentation site alongside the configuration or feature being deprecated.
  • Output a log at the WARN level if Vector detects deprecated configuration or features being used on start-up, during vector validate, or at runtime, when possible. This log message will lead with the text DEPRECATED to make it easy to filter for.

Migration

Users will have 1 or more minor releases to migrate away from using the deprecation using the instructions provided in the deprecation notice.

Removal

A deprecated configuration option or feature in Vector is removed.

When this happens, we will notify by:

  • Listing the removal in the Breaking Changes section of upgrade guide for that release. This will include directions on how to transition if applicable.

When possible, Vector will error at start-up when a removed configuration option or feature is used.

Process

When introducing a deprecation into Vector, the pull request introducing the deprecation should:

  • Add a note to the Deprecations section of the upgrade guide for the next release with a description and directions for transitioning if applicable.
  • Add a deprecation note to the docs. Typically this means adding deprecation: "description of the deprecation" to the cue data for the option or feature. If the cue schema does not support deprecation for whatever you are deprecating yet, add it to the schema and open an issue to have it rendered on the website.
  • Add a log message to Vector that is logged at the WARN level starting with the word DEPRECATION if Vecor detects the deprecated configuration or feature being used (when possible).

When removing a deprecation in a subsequent release, the pull request should:

  • Indicate that it is a breaking change by including ! in the title after the type/scope
  • Remove the deprecation from the documentation
  • Add a note to the Breaking Changes section of the upgrade guide for the next release with a description and directions for transitioning if applicable.