Convert RestClient to Gitlab::HTTP for Prometheus Monitor

- Closes #60024

- Change PrometheusClient.new to accept a base url instead of an
  already created RestClient

- Use Gitlab::HTTP in PrometheusClient instead of creating RestClient
  in PrometheusService

- Move http_options from PrometheusService to
  PrometheusClient (follow_redirects: false)

- ensure that base urls don't have the trailing slash

- Created a `PrometheusClient#url` method that might not be strictly
  required

- Change rescued exceptions from RestClient::* to
  HTTParty::ResponseError where possible and StandardError for the
  rest

3 files changed, 7 insertions, 10 deletions

diff --git a/app/models/clusters/applications/prometheus.rb b/app/models/clusters/applications/prometheus.rb
index 5eb535cab58..08e52f32bb3 100644
--- a/app/models/clusters/applications/prometheus.rb
+++ b/app/models/clusters/applications/prometheus.rb
@@ -83,7 +83,7 @@ module Clusters
 
         # 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)
+        Gitlab::PrometheusClient.new(proxy_url, options)
       rescue Kubeclient::HttpError
         # If users have mistakenly set parameters or removed the depended clusters,
         # `proxy_url` could raise an exception because gitlab can not communicate with the cluster.
diff --git a/app/models/concerns/prometheus_adapter.rb b/app/models/concerns/prometheus_adapter.rb
index c2542dbe743..9ac4722c6b1 100644
--- a/app/models/concerns/prometheus_adapter.rb
+++ b/app/models/concerns/prometheus_adapter.rb
@@ -14,10 +14,6 @@ module PrometheusAdapter
       raise NotImplementedError
     end
 
-    def prometheus_client_wrapper
-      Gitlab::PrometheusClient.new(prometheus_client)
-    end
-
     def can_query?
       prometheus_client.present?
     end
@@ -35,7 +31,7 @@ module PrometheusAdapter
     def calculate_reactive_cache(query_class_name, *args)
       return unless prometheus_client
 
-      data = Object.const_get(query_class_name, false).new(prometheus_client_wrapper).query(*args)
+      data = Object.const_get(query_class_name, false).new(prometheus_client).query(*args)
       {
         success: true,
         data: data,
diff --git a/app/models/project_services/prometheus_service.rb b/app/models/project_services/prometheus_service.rb
index c68a9d923c8..6eff2ea2e3a 100644
--- a/app/models/project_services/prometheus_service.rb
+++ b/app/models/project_services/prometheus_service.rb
@@ -63,15 +63,16 @@ class PrometheusService < MonitoringService
 
   # Check we can connect to the Prometheus API
   def test(*args)
-    Gitlab::PrometheusClient.new(prometheus_client).ping
-
+    prometheus_client.ping
     { success: true, result: 'Checked API endpoint' }
   rescue Gitlab::PrometheusClient::Error => err
     { success: false, result: err }
   end
 
   def prometheus_client
-    RestClient::Resource.new(api_url, max_redirects: 0) if should_return_client?
+    return unless should_return_client?
+
+    Gitlab::PrometheusClient.new(api_url)
   end
 
   def prometheus_available?
@@ -84,7 +85,7 @@ class PrometheusService < MonitoringService
   private
 
   def should_return_client?
-    api_url && manual_configuration? && active? && valid?
+    api_url.present? && manual_configuration? && active? && valid?
   end
 
   def synchronize_service_state