Current state: Accepted
Discussion thread: here
JIRA: KAFKA-13510
Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).
When starting a connector, users must provide the connector configuration. The configuration often also includes configurations for other plugins such as SMTs or converters. Today, Connect does not provide a way to see what plugins are installed apart from connectors. This make it difficult for users building data pipeline to know which plugins are available and what is possible. Basically they have to know how the Connect runtime is set up. Even once they know the plugins that are available, they then have to go look at the plugins documentation or, in the worst case, look directly at the source code to find their configuration definitions.
Connector plugins should be discoverable via the REST API. Their configuration definitions should also be easily retrieved. This would significantly ease the process of building pipelines and enable building tools and UIs that can manage Connect data pipelines.
GET /connector-plugins: This endpoint will be updated to allow listing all plugins. The response structure of the objects in the array remain unchanged. A new query parameter "connectorsOnly" will be added and it will default to true so it's fully compatible with the current behavior. Users will be able to list all Connectors, Transformations, Converters, HeaderConverters and Predicates plugins by setting it to false. Classes that implement multiple plugin types will appear once for each type. For example SimpleHeaderConverter will be listed as a converter and as a header_converter. Possible values for the "type" field are "sink", "source", "converter", "header_converter", "transformation" and "predicate".For example GET /connector-plugins?connectorsOnly=false will return:
[
{
"class": "org.apache.kafka.connect.file.FileStreamSinkConnector",
"type": "sink",
"version": "3.2.0"
},
{
"class": "org.apache.kafka.connect.file.FileStreamSourceConnector",
"type": "source",
"version": "3.2.0"
}, {
"class": "org.apache.kafka.connect.converters.ByteArrayConverter",
"type": "converter"
},
{
"class": "org.apache.kafka.connect.transforms.Cast$Value",
"type": "transformation"
},
{
"class": "org.apache.kafka.connect.transforms.predicates.HasHeaderKey",
"type": "predicate"
},
{
"class": "org.apache.kafka.connect.storage.SimpleHeaderConverter",
"type": "header_converter"
},
{
"class": "org.apache.kafka.connect.storage.SimpleHeaderConverter",
"type": "converter"
},
...
] |
Currently only Connector plugins are versioned, so we won't include the version field for other plugins.
GET /connector-plugins/<plugin>/config: This new endpoint will return the configuration definitions of the specified plugin. It will work with all plugins returned by /connector_plugins.The plugin can be specified via its fully qualified class name or its Connect alias like in the existing /connector-plugins/<plugin>/config/validate endpoint. If a plugin does not override the config() method, the response is an empty array.
For example, accessing http://localhost:8083/connector-plugins/org.apache.kafka.connect.transforms.Cast$Value/config will return:
[
{
"name": "spec",
"type": "LIST",
"required": true,
"default_value": null,
"importance": "HIGH",
"documentation": "List of fields and the type to cast them to of the form field1:type,field2:type to cast fields of Maps or Structs. A single type to cast the entire value. Valid types are int8, int16, int32, int64, float32, float64, boolean, and string. Note that binary fields can only be cast to string.",
"group": null,
"width": "NONE",
"display_name": "spec",
"dependents": [],
"order": -1
}
] |
REST API:
ConnectorPluginsResource to retrieve the plugin configuration definitions@GET
@Path("/{plugin}/config")
public List<ConfigKeyInfo> getPluginConfig() {} |
connectorsOnly" that defaults to true@GET
@Path("/")
public List<ConnectorPluginInfo> listConnectorPlugins(@DefaultValue("true") @QueryParam("connectorsOnly") boolean connectorsOnly) {} |
Converter interface:
Add a config() method to Converter with a default implementation.
public interface Converter {
[...]
/**
* Configuration specification for this set of converters.
* @return the configuration specification; may not be null
*/
default ConfigDef config() {
return new ConfigDef();
}
} |
It's common for custom converters to implement both Converter and HeaderConverter. As the 2 methods to retrieve the ConfigDef will have exactly the same signature, it will still be possible to implement both interfaces.
/connector-plugins keeps its current behavior and will only expose the new behavior when a new query parameter is set./connector-plugins/<plugin>/config on existing converters that don't implement the config() method, an empty array will be returned. If a converter is also implementing HeaderConverter, and hence already have a config() method, it will be automatically used and the config will be returned./connector-plugins/<plugin>/config is a new endpoint that doesn't cause compatibility issues.I propose to flip the query parameter value to list all plugins by default in the next major release.