Move client creation to Prometheus Application, manufacture proper rest client

app/models/clusters/applications/prometheus.rb

@@ -14,10 +14,6 @@ module Clusters
         'stable/prometheus'
       end
-      def namespace
-        Gitlab::Kubernetes::Helm::NAMESPACE
-      end
-
       def service_name
         'prometheus-prometheus-server'
       end
@@ -33,6 +29,17 @@ module Clusters
       def install_command
         Gitlab::Kubernetes::Helm::InstallCommand.new(name, chart: chart, chart_values_file: chart_values_file)
       end
+
+      def proxy_client
+        return unless cluster.kubeclient
+
+        kube_client = cluster.kubeclient
+        proxy_url = kube_client.proxy_url('service', service_name, service_port, Gitlab::Kubernetes::Helm::NAMESPACE)
+
+        # ensures headers containing auth data are appended to original k8s client options
+        options = kube_client.rest_client.options.merge(headers: kube_client.headers)
+        RestClient::Resource.new(proxy_url, options)
+      end
     end
   end
 end

app/models/project_services/prometheus_service.rb

@@ -86,7 +86,7 @@ class PrometheusService < MonitoringService
   # Cache metrics for specific environment
   def calculate_reactive_cache(query_class_name, environment_id, *args)
     return unless active? && project && !project.pending_delete?
-    client = client_for_environment(environment_id)
+    client = client(environment_id)
     data = Kernel.const_get(query_class_name).new(client).query(environment_id, *args)
@@ -101,12 +101,16 @@ class PrometheusService < MonitoringService
   def client(environment_id)
     if manual_mode?
-      Gitlab::PrometheusClient.new(api_url: api_url)
+      Gitlab::PrometheusClient.new(RestClient::Resource.new(api_url))
     else
-      cluster(environment_id)
+      cluster = find_cluster_with_prometheus(environment_id)
+
+      Gitlab::PrometheusClient.new(cluster.application_prometheus.proxy_client) if cluster
     end
   end
+  private
+
   def find_cluster_with_prometheus(environment_id)
     clusters = if environment_id
                  ::Environment.find_by(id: environment_id).try(:enabled_clusters) || []
@@ -117,33 +121,6 @@ class PrometheusService < MonitoringService
     clusters.detect { |cluster| cluster.application_prometheus.installed? }
   end
-  private
-
-  def client_for_environment(environment_id)
-    cluster = find_cluster_with_prometheus(environment_id)
-    return unless cluster
-
-    prometheus = cluster.application_prometheus
-
-    client_through_kube_proxy(cluster.kubeclient,
-                              'service',
-                              prometheus.service_name,
-                              prometheus.service_port,
-                              prometheus.namespace) if cluster.kubeclient
-  end
-
-  def client_through_kube_proxy(kube_client, kind, name, port, namespace = '')
-    rest_client = kube_client.rest_client
-    base_url = rest_client.url
-    proxy_url = kube_client.proxy_url(kind, name, port, namespace)
-
-    Rails.logger.warn rest_client[proxy_url.sub(base_url, '')]
-    Rails.logger.warn proxy_url.sub(base_url, '')
-
-    Gitlab::PrometheusClient.new(api_url: api_url, rest_client: rest_client[proxy_url.sub(base_url, '')], headers: kube_client.headers)
-  end
-
-
   def rename_data_to_metrics(metrics)
     metrics[:metrics] = metrics.delete :data
     metrics

lib/gitlab/prometheus_client.rb

@@ -3,12 +3,10 @@ module Gitlab
   # Helper methods to interact with Prometheus network services & resources
   class PrometheusClient
-    attr_reader :api_url, :rest_client, :headers
-    def initialize(api_url:, rest_client: nil, headers: nil)
-      @api_url = api_url
+    attr_reader :rest_client, :headers
+    def initialize(rest_client)
       @rest_client = rest_client || RestClient::Resource.new(api_url)
-      @headers = headers || {}
     end
     def ping
@@ -49,7 +47,7 @@ module Gitlab
     end
     def get(path, args)
-      response = rest_client[path].get(headers.merge(params: args))
+      response = rest_client[path].get(params: args)
       handle_response(response)
     rescue SocketError
       raise PrometheusError, "Can't connect to #{url}"
@@ -60,7 +58,7 @@ module Gitlab
     end
     def handle_response(response)
-      json_data = json_response(response)
+      json_data = JSON.parse(response.body)
       if response.code == 200 && json_data['status'] == 'success'
         json_data['data'] || {}
       elsif response.code == 400
@@ -70,10 +68,6 @@ module Gitlab
       end
     end
-    def json_response(response)
-      JSON.parse(response.body)
-    end
-
     def get_result(expected_type)
       data = yield
       data['result'] if data['resultType'] == expected_type