Merge branch 'master' into 'docs/fix-example-dot-net'

# Conflicts:
#   doc/user/project/clusters/serverless/index.md

1 files changed, 116 insertions, 0 deletions

diff --git a/app/services/prometheus/proxy_service.rb b/app/services/prometheus/proxy_service.rb
new file mode 100644
index 00000000000..c5d2b84878b
--- /dev/null
+++ b/app/services/prometheus/proxy_service.rb
@@ -0,0 +1,116 @@
+# frozen_string_literal: true
+
+module Prometheus
+  class ProxyService < BaseService
+    include ReactiveCaching
+    include Gitlab::Utils::StrongMemoize
+
+    self.reactive_cache_key = ->(service) { service.cache_key }
+    self.reactive_cache_lease_timeout = 30.seconds
+    self.reactive_cache_refresh_interval = 30.seconds
+    self.reactive_cache_lifetime = 1.minute
+    self.reactive_cache_worker_finder = ->(_id, *args) { from_cache(*args) }
+
+    attr_accessor :proxyable, :method, :path, :params
+
+    PROXY_SUPPORT = {
+      'query' => {
+        method: ['GET'],
+        params: %w(query time timeout)
+      },
+      'query_range' => {
+        method: ['GET'],
+        params: %w(query start end step timeout)
+      }
+    }.freeze
+
+    def self.from_cache(proxyable_class_name, proxyable_id, method, path, params)
+      proxyable_class = begin
+        proxyable_class_name.constantize
+      rescue NameError
+        nil
+      end
+      return unless proxyable_class
+
+      proxyable = proxyable_class.find(proxyable_id)
+
+      new(proxyable, method, path, params)
+    end
+
+    # proxyable can be any model which responds to .prometheus_adapter
+    # like Environment.
+    def initialize(proxyable, method, path, params)
+      @proxyable = proxyable
+      @path = path
+
+      # Convert ActionController::Parameters to hash because reactive_cache_worker
+      # does not play nice with ActionController::Parameters.
+      @params = filter_params(params, path).to_hash
+
+      @method = method
+    end
+
+    def id
+      nil
+    end
+
+    def execute
+      return cannot_proxy_response unless can_proxy?
+      return no_prometheus_response unless can_query?
+
+      with_reactive_cache(*cache_key) do |result|
+        result
+      end
+    end
+
+    def calculate_reactive_cache(proxyable_class_name, proxyable_id, method, path, params)
+      return no_prometheus_response unless can_query?
+
+      response = prometheus_client_wrapper.proxy(path, params)
+
+      success(http_status: response.code, body: response.body)
+    rescue Gitlab::PrometheusClient::Error => err
+      service_unavailable_response(err)
+    end
+
+    def cache_key
+      [@proxyable.class.name, @proxyable.id, @method, @path, @params]
+    end
+
+    private
+
+    def service_unavailable_response(exception)
+      error(exception.message, :service_unavailable)
+    end
+
+    def no_prometheus_response
+      error('No prometheus server found', :service_unavailable)
+    end
+
+    def cannot_proxy_response
+      error('Proxy support for this API is not available currently')
+    end
+
+    def prometheus_adapter
+      strong_memoize(:prometheus_adapter) do
+        @proxyable.prometheus_adapter
+      end
+    end
+
+    def prometheus_client_wrapper
+      prometheus_adapter&.prometheus_client_wrapper
+    end
+
+    def can_query?
+      prometheus_adapter&.can_query?
+    end
+
+    def filter_params(params, path)
+      params.slice(*PROXY_SUPPORT.dig(path, :params))
+    end
+
+    def can_proxy?
+      PROXY_SUPPORT.dig(@path, :method)&.include?(@method)
+    end
+  end
+end