Support Central Config

CHANGELOG.md

@@ -4,6 +4,12 @@ All notable changes to this project will be documented in this file.
 
 This project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
+## Unreleased
+
+### Added
+
+- Support for APM Agent Configuration via Kibana ([#464](https://github.com/elastic/apm-agent-ruby/pull/464))
+
 ## 2.9.1 (2019-06-28)
 
 ### Fixed

docs/configuration.asciidoc

@@ -213,6 +213,19 @@ Whether or not to attach the request headers to transactions and errors.
 
 Whether or not to attach `ENV` from Rack to transactions and errors.
 
+[float]
+[[config-central-config]]
+==== `central_config`
+|============
+| Environment                  | `Config` key     | Default
+| `ELASTIC_APM_CENTRAL_CONFIG` | `central_config` | `true`
+|============
+
+Enable {kibana-ref}/agent-configuration.html[APM Agent Configuration via Kibana].
+If set to `true`, the client will poll the APM Server regularly for new agent configuration.
+
+NOTE: This feature requires APM Server v7.3 or later and that the APM Server is configured with `kibana.enabled: true`.
+
 [float]
 [[config-custom-key-filters]]
 ==== `custom_key_filters`

lib/elastic_apm/agent.rb

@@ -1,13 +1,17 @@
 # frozen_string_literal: true
 
+require 'elastic_apm/error'
+
 require 'elastic_apm/context_builder'
 require 'elastic_apm/error_builder'
 require 'elastic_apm/stacktrace_builder'
-require 'elastic_apm/error'
+
+require 'elastic_apm/central_config'
 require 'elastic_apm/transport/base'
-require 'elastic_apm/spies'
 require 'elastic_apm/metrics'
 
+require 'elastic_apm/spies'
+
 module ElasticAPM
   # rubocop:disable Metrics/ClassLength
   # @api private
@@ -57,20 +61,23 @@ def self.running?
       !!@instance
     end
 
+    # rubocop:disable Metrics/MethodLength
     def initialize(config)
       @config = config
 
       @stacktrace_builder = StacktraceBuilder.new(config)
       @context_builder = ContextBuilder.new(config)
       @error_builder = ErrorBuilder.new(self)
 
+      @central_config = CentralConfig.new(config)
       @transport = Transport::Base.new(config)
       @instrumenter = Instrumenter.new(
         config,
         stacktrace_builder: stacktrace_builder
       ) { |event| enqueue event }
       @metrics = Metrics.new(config) { |event| enqueue event }
     end
+    # rubocop:enable Metrics/MethodLength
 
     attr_reader :config, :transport, :instrumenter,
       :stacktrace_builder, :context_builder, :error_builder, :metrics

lib/elastic_apm/central_config.rb

@@ -0,0 +1,136 @@
+# frozen_string_literal: true
+
+require 'elastic_apm/central_config/cache_control'
+
+module ElasticAPM
+  # @api private
+  class CentralConfig
+    include Logging
+
+    # @api private
+    class ResponseError < InternalError
+      def initialize(response)
+        @response = response
+      end
+
+      attr_reader :response
+    end
+    class ClientError < ResponseError; end
+    class ServerError < ResponseError; end
+
+    DEFAULT_MAX_AGE = 300
+
+    def initialize(config)
+      @config = config
+      @modified_options = {}
+      @service_info = {
+        'service.name': config.service_name,
+        'service.environment': config.environment
+      }.to_json
+    end
+
+    attr_reader :config, :task
+
+    def start
+      return unless config.central_config?
+
+      fetch_and_apply_config
+    end
+
+    def fetch_and_apply_config
+      Concurrent::Promise
+        .execute(&method(:fetch_config))
+        .on_success(&method(:handle_success))
+        .rescue(&method(:handle_error))
+    end
+
+    def stop
+      @task&.cancel
+    end
+
+    # rubocop:disable Metrics/MethodLength
+    def fetch_config
+      resp = perform_request
+
+      case resp.status
+      when 200..299
+        resp
+      when 300..399
+        resp
+      when 400..499
+        raise ClientError, resp
+      when 500..599
+        raise ServerError, resp
+      end
+    end
+    # rubocop:enable Metrics/MethodLength
+
+    def assign(update)
+      # For each updated option, store the original value,
+      # unless already stored
+      update.each_key do |key|
+        @modified_options[key] ||= config.get(key.to_sym)&.value
+      end
+
+      # If the new update doesn't set a previously modified option,
+      # revert it to the original
+      @modified_options.each_key do |key|
+        next if update.key?(key)
+        update[key] = @modified_options.delete(key)
+      end
+
+      config.assign(update)
+    end
+
+    private
+
+    def handle_success(resp)
+      # 304 Not Modified
+      unless resp.status == 304
+        update = JSON.parse(resp.body.to_s)
+        assign(update)
+      end
+
+      info 'Updated config from APM Server'
+
+      schedule_next_fetch(resp)
+
+      true
+    rescue Exception => e
+      error 'Failed to apply remote config, %s', e.inspect
+      debug { e.backtrace.join('\n') }
+    end
+
+    def handle_error(error)
+      error(
+        'Failed fetching config: %s, trying again in %d seconds',
+        error.response.body, DEFAULT_MAX_AGE
+      )
+
+      assign({})
+
+      schedule_next_fetch(error.response)
+    end
+
+    def perform_request
+      Http.post(
+        config.server_url + '/agent/v1/config/',
+        body: @service_info,
+        headers: { etag: 1, content_type: 'application/json' }
+      )
+    end
+
+    def schedule_next_fetch(resp)
+      seconds =
+        if (cache_header = resp.headers['Cache-Control'])
+          CacheControl.new(cache_header).max_age
+        else
+          DEFAULT_MAX_AGE
+        end
+
+      @task =
+        Concurrent::ScheduledTask
+        .execute(seconds, &method(:fetch_and_apply_config))
+    end
+  end
+end

lib/elastic_apm/central_config/cache_control.rb

@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+module ElasticAPM
+  class CentralConfig
+    # @api private
+    class CacheControl
+      def initialize(value)
+        @header = value
+        parse!(value)
+      end
+
+      attr_reader(
+        :must_revalidate,
+        :no_cache,
+        :no_store,
+        :no_transform,
+        :public,
+        :private,
+        :proxy_revalidate,
+        :max_age,
+        :s_maxage
+      )
+
+      private
+
+      def parse!(value)
+        value.split(',').each do |token|
+          k, v = token.split('=').map(&:strip)
+          instance_variable_set(:"@#{k.gsub('-', '_')}", v ? v.to_i : true)
+        end
+      end
+    end
+  end
+end

lib/elastic_apm/config.rb

@@ -41,6 +41,7 @@ class Config
     option :capture_body,                      type: :string, default: 'off'
     option :capture_headers,                   type: :bool,   default: true
     option :capture_env,                       type: :bool,   default: true
+    option :central_config,                    type: :bool,   default: true
     option :current_user_email_method,         type: :string, default: 'email'
     option :current_user_id_method,            type: :string, default: 'id'
     option :current_user_username_method,      type: :string, default: 'username'

lib/elastic_apm/config/options.rb

@@ -112,6 +112,11 @@ def method_missing(name, *value)
         end
         # rubocop:enable Metrics/MethodLength, Metrics/AbcSize
 
+        def [](key)
+          options[key]
+        end
+        alias :get :[]
+
         def set(key, value)
           options.fetch(key.to_sym).set(value)
         rescue KeyError

spec/elastic_apm/central_config/cache_control_spec.rb

@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+
+module ElasticAPM
+  RSpec.describe CentralConfig::CacheControl do
+    let(:header) { nil }
+    subject { described_class.new(header) }
+
+    context 'with max-age' do
+      let(:header) { 'max-age=300' }
+      its(:max_age) { should be 300 }
+      its(:must_revalidate) { should be nil }
+    end
+
+    context 'with must-revalidate' do
+      let(:header) { 'must-revalidate' }
+      its(:max_age) { should be nil }
+      its(:must_revalidate) { should be true }
+    end
+
+    context 'with multiple values' do
+      let(:header) { 'must-revalidate, public, max-age=300' }
+      its(:max_age) { should be 300 }
+      its(:must_revalidate) { should be true }
+      its(:public) { should be true }
+      its(:private) { should be nil }
+    end
+  end
+end