Add cron worker to automatically rollout zoekt exact code search to paid namespaces

What does this MR do and why?

Duo summary:

This merge request introduces a new Zoekt rollout system for search functionality. It adds a planning service to determine how to distribute search indices across available nodes, a provisioning service to execute the planned changes, and a rollout service to orchestrate the entire process. The changes also include a new worker to periodically run the rollout process, along with associated configuration and feature flag settings. Additionally, there are minor adjustments to existing models and scopes to support these new features. Overall, this update aims to improve the management and distribution of search indices across the system's infrastructure.

This is all behind the feature flag zoekt_rollout_worker

References

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• #508836 (closed)

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ee/app/services/search/zoekt/planning_service.rb

+# frozen_string_literal: true
+
+module Search
+  module Zoekt
+    class PlanningService
+      PRE_READY_LIMIT = 1
+
+      attr_reader :enabled_namespaces, :nodes, :options
+
+      def self.plan(**kwargs)
+        new(**kwargs).plan
+      end
+
+      def initialize(
+        enabled_namespaces:, nodes: nil, **options)
+        @enabled_namespaces = Array(enabled_namespaces)
+        @nodes = nodes || load_nodes_with_unclaimed_storage
+        @options = options
+      end
+
+      def plan
+        namespace_plans = enabled_namespaces.map do |enabled_namespace|
+          Plan.new(
+            enabled_namespace: enabled_namespace,
+            nodes: nodes,
+            **options
+          ).generate
+        end
+
+        {
+          total_required_storage_bytes: namespace_plans.sum { |plan| plan[:namespace_required_storage_bytes] },
+          namespaces: namespace_plans
+        }
+      end
+
+      private
+
+      def load_nodes_with_unclaimed_storage
+        ::Search::Zoekt::Node
+          .with_positive_unclaimed_storage_bytes
+          .select { |node| Search::Zoekt::Index.for_node(node).pre_ready.count <= PRE_READY_LIMIT }
+          .map do |node|
+            {
+              id: node.id,
+              unclaimed_storage_bytes: node.unclaimed_storage_bytes,
+              indices: [],
+              node: node
+            }
+          end
+      end
+
+      class Plan
+        attr_reader :enabled_namespace, :namespace, :num_replicas, :buffer_factor, :batch_size,
+          :max_indices_per_replica, :errors, :replica_plans, :nodes
+
+        def initialize(
+          enabled_namespace:, num_replicas:, nodes:,
+          buffer_factor: 3, batch_size: 500, max_indices_per_replica: 5)
+          @enabled_namespace = enabled_namespace
+          @namespace = enabled_namespace.namespace
+          @num_replicas = num_replicas
+          @buffer_factor = buffer_factor
+          @batch_size = batch_size
+          @max_indices_per_replica = max_indices_per_replica
+          @errors = []
+          @replica_plans = []
+          @nodes = nodes
+          @used_node_ids = Set.new
+        end
+
+        def generate
+          num_replicas.times { simulate_replica_plan }
+
+          {
+            namespace_id: namespace.id,
+            enabled_namespace_id: enabled_namespace.id,
+            namespace_required_storage_bytes: calculate_namespace_storage,
+            replicas: replica_plans,
+            errors: errors
+          }
+        end
+
+        private
+
+        def simulate_replica_plan
+          replica_indices = []
+
+          fetch_projects.each_batch(of: batch_size) do |batch|
+            batch.each do |project|
+              stats = project.statistics
+
+              if replica_indices.size >= max_indices_per_replica
+                log_error(replica_plans.size, :index_limit_exceeded,
+                  "Replica reached maximum index limit (#{max_indices_per_replica})")
+                break
+              end
+
+              assign_to_node(stats, replica_indices)
+            end
+          end
+
+          add_replica_plan(replica_indices)
+        end
+
+        def fetch_projects
+          namespace.all_projects
+                  .with_statistics
+                  .joins(:statistics)
+                  .group('projects.id, project_statistics.id, repository_size')
+                  .order('repository_size DESC, projects.id ASC')
+        end
+
+        def assign_to_node(stats, replica_indices)
+          best_node = find_best_node(stats)
+
+          if best_node
+            assign_project_to_index(best_node, stats, replica_indices)
+          else
+            log_error(replica_plans.size, :node_unavailable,
+              "No node can accommodate project #{stats.project_id} with size #{scaled_size(stats)}")
+          end
+        end
+
+        def find_best_node(stats)
+          nodes
+            .reject { |node| @used_node_ids.include?(node[:id]) }
+            .select { |node| node[:unclaimed_storage_bytes] && node[:unclaimed_storage_bytes] >= scaled_size(stats) }
+            .max_by { |node| node[:unclaimed_storage_bytes] }
+        end
+
+        def assign_project_to_index(node, stats, replica_indices)
+          project_size = scaled_size(stats)
+
+          index = replica_indices
+                    .select { |idx| idx[:required_storage_bytes] + project_size <= idx[:max_storage_bytes] }
+                    .min_by { |idx| idx[:max_storage_bytes] - (idx[:required_storage_bytes] + project_size) }
+
+          unless index
+            if replica_indices.size >= max_indices_per_replica
+              log_error(nil, :index_limit_exceeded, "Max indices per replica reached")
+              return
+            end
+
+            index = simulate_index(node)
+            replica_indices << index
+            node[:indices] << index
+            @used_node_ids.add(node[:id])
+          end
+
+          add_project_to_index(index, stats)
+          node[:unclaimed_storage_bytes] -= project_size
+        end
+
+        def simulate_index(node)
+          {
+            node_id: node[:id],
+            projects: { project_id_from: nil, project_id_to: nil },
+            required_storage_bytes: 0,
+            max_storage_bytes: node[:unclaimed_storage_bytes]
+          }
+        end
+
+        def add_project_to_index(index, stats)
+          index[:projects][:project_id_from] ||= stats.project_id
+          index[:projects][:project_id_to] = stats.project_id
+          index[:required_storage_bytes] += scaled_size(stats)
+        end
+
+        def add_replica_plan(replica_indices)
+          replica_indices.last[:projects][:project_id_to] = nil if replica_indices.any?
+
+          replica_plans << { indices: replica_indices.map { |index| format_index(index) } }
+        end
+
+        def format_index(index)
+          index.slice(:node_id, :projects, :required_storage_bytes, :max_storage_bytes)
+        end
+
+        def calculate_namespace_storage
+          replica_plans.sum { |replica| replica[:indices].sum { |index| index[:required_storage_bytes] } }
+        end
+
+        def scaled_size(stats)
+          stats.repository_size * buffer_factor
+        end
+
+        def log_error(replica_idx, type, details)
+          @errors << { namespace_id: namespace.id, replica_idx: replica_idx, type: type, details: details }
+        end
+      end
+    end
+  end
+end