1.0: Update usage of new service discovery helper API

Since v1.13.0 new helper API is introduced.
It makes supporting service_discovery easy.

ref. fluent/fluentd#3299

Signed-off-by: Kentaro Hayashi <[email protected]>

Author: kenhys

plugin-helper-overview/api-plugin-helper-service_discovery.md

@@ -17,20 +17,16 @@ module Fluent::Plugin
     def configure(conf)
       super
 
-      config = conf.elements(name: 'service_discovery').map do |s|
-        { type: :static, conf: s }
-      end
-
       # 2. Create and start service discovery manager
-      service_discovery_create_manager(
+      service_discovery_configure(
         :out_example_service_discovery_watcher,
-        configurations: config,
+        static_default_service_directive: 'server'
       )
     end
 
     def write(chunk)
       # 3. Select service to send data
-      discovery_manager.select_service do |node|
+      service_discovery_select_service do |node|
         send_data(node, chunk)
       end
     end
@@ -46,6 +42,18 @@ end
 
 ## Methods
 
+### `service_discovery_configure(title, static_default_service_directive: nil, load_balancer: nil, custom_build_method: nil, interval: 3)`
+
+Since v1.13.0, `discovery_manager` is almost automatically configured only by calling this method.
+
+#### Parameters
+
+* `title`: Thread name. Must be unique. \(required\)
+* `static_default_service_directive`: The directive name of each service when "static" service discovery is enabled in default.
+* `load_balancer`: object which has two methods #rebalance and #select_service.
+* `custom_build_method`: The custom method to build the service.
+* `interval`: Time interval for updating target service.
+
 ### `service_discovery_create_manager(title, configurations:, load_balancer: nil, custom_build_method: nil, interval: 3)`
 
 This method creates `service_discovery_manager`.
@@ -66,5 +74,63 @@ It manages service discovery functionalities such as updating target services an
 
 * [`out_forward`](../output/forward.md)
 
+## Migration guide from `service_discovery_create_manager` to more simpler helper method
+
+Here is the guide to migrate to newer API which is available since v1.13.0.
+
+Example:
+
+```ruby
+require 'fluent/plugin/output'
+
+module Fluent::Plugin
+  class ExampleOutput < Output
+    Fluent::Plugin.register_output('example', self)
+
+    helpers :service_discovery
+
+    def configure(conf)
+      super
+
+      # 1. Remove the following code which parse 'service_discovery' section by yourself
+      #
+      # config = conf.elements(name: 'service_discovery').map do |s|
+      #  { type: :static, conf: s }
+      # end
+
+      # 2. Remove the following code and use service_discovery_configure
+      #
+      # service_discovery_create_manager(
+      #  :out_example_service_discovery_watcher,
+      #  configurations: config,
+      # )
+      service_discovery_configure(
+        :out_example_service_discovery_watcher,
+        static_default_service_directive: 'server'
+      )
+    end
+
+    def write(chunk)
+      # 3. Remove the following code and use service_discovery_select_service to select service
+      #
+      # @discovery_manager.select_service do |node|
+      #  send_data(node, chunk)
+      # end
+      service_discovery_select_service do |node|
+        send_data(node, chunk)
+      end
+    end
+
+    def send_data(node, chunk)
+      # Send data
+    end
+  end
+end
+```
+
+You can also use helper methods such as `service_discovery_services` or `service_discovery_rebalance` instead of
+`@discovery_manager.services` or `@discovery_manager.rebalance`.
+
+
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