ECS Compatibility Support Mixin

This gem provides an API-compatible implementation of ECS-compatiblity mode, allowing plugins to be explicitly configured with ecs_compatibility in a way that respects pipeline- and process-level settings where they are available. It can be added as a dependency of any plugin that wishes to implement one or more ECS-compatibility modes while still supporting older Logstash versions.

Usage (simple)

Add version ~>1.0 of this gem as a runtime dependency of your Logstash plugin's gemspec:

Gem::Specification.new do |s|
  # ...

  s.add_runtime_dependency 'logstash-mixin-ecs_compatibility_support', '~>1.0'
end

In your plugin code, require this library and include it into your plugin class that already inherits LogStash::Plugin:

require 'logstash/plugin_mixins/ecs_compatibility_support'

class LogStash::Inputs::Foo < Logstash::Inputs::Base
  include LogStash::PluginMixins::ECSCompatibilitySupport

  # ...
end

Use the ecs_compatibility method, which will reflect the user's desired ECS-Compatibility mode (either :disabled or a symbol holding a v-prefixed integer major version of ECS, e.g., :v1) after the plugin has been sent #config_init; your plugin does not need to know whether the user specified the value in their plugin config or its value was provided by Logstash.

Care should be taken to handle all possible values:
- all ECS major versions that are supported by the plugin
- ECS Compatibility being disabled
- helpful failure when an unsupported version is requested
```
  def register
    case ecs_compatibility
    when :disabled
      # ...
    when :v1
      # ...
    else
      fail(NotImplementedError, "ECS #{ecs_compatibility} is not supported by this plugin.")
    end
  end
```

Usage (advanced)

Release 1.1 of this support gem includes support for constraining a plugin to only operate in specified ECS-Compatibility modes, and advanced support for runtime selectors that provide developers a way to provide alternate values during initialization based on the instantiated plugin's effective ecs_compatibility mode. This is helpful in plugins that define large field mappings, because it allows those mappings to be side-by-side where they are unlikely to diverge and introduce bugs.

Add version ~>1.2 of this gem as a runtime dependency of your Logstash plugin's gemspec:

Gem::Specification.new do |s|
  # ...

  s.add_runtime_dependency 'logstash-mixin-ecs_compatibility_support', '~>1.2'
end

In your plugin code, require this library and include it into your plugin class that already inherits LogStash::Plugin, but this time specify which versions of ECS your plugin supports:
```
require 'logstash/plugin_mixins/ecs_compatibility_support'

class LogStash::Inputs::Foo < Logstash::Inputs::Base
  include LogStash::PluginMixins::ECSCompatibilitySupport(:disabled,:v1)

  # ...
end
```
This prevents the plugin from being instantiated with an unsupported mode, whether that mode was explicitly defined for the plugin instance or implictly defined by the pipeline in which the plugin is run.

You can also optionally provide an alias mapping, for when your plugin supports multiple versions of ECS that are largely identical to each other. This can be especially helpful when using ecs_select.
```
require 'logstash/plugin_mixins/ecs_compatibility_support'

class LogStash::Inputs::Foo < Logstash::Inputs::Base
  include LogStash::PluginMixins::ECSCompatibilitySupport(:disabled,:v1,:v8 => :v1)

  # ...
end
```
As in the simple usage example, you can use the ecs_compatibility method.

But when supported versions are specified, you can also use the ecs_select method to define alternates in-line. At runtime, the correct value will be selected based on the current effective ecs_compatibility mode.
```
  def register
    @field_hostname = ecs_select[disabled: "hostname", v1: "[host][name]"]
    @field_hostip   = ecs_select[disabled: "ip",       v1: "[host][ip]"  ]
  end
```
If you initialized the mixin with an alias mapping, missing values will be resolved by their alias.

NOTE: ecs_select should only be used during plugin initialization and not during event-by-event processing.

Development

This gem:

MUST remain API-stable at 1.x
MUST NOT introduce additional runtime dependencies

andsel/logstash-mixin-ecs_compatibility_support

ECS Compatibility Support Mixin

Usage (simple)

Usage (advanced)

Development