Include CRUD endpoints for Cluster API

Adds the following initial CRUD endpoints for Clusters API:

- GET list of clusters
- GET specific cluster
- POST add existing cluster (mimic of "Add cluster")
- PUT update cluser
- DELETE destroy cluster

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/40473

changelogs/unreleased/40473-api-support-for-kubernetes-integration.yml

+---
+title: Add API Support for Kubernetes integration
+merge_request: 23922
+author:
+type: added

lib/api/api.rb

@@ -129,6 +129,7 @@ module API
     mount ::API::PagesDomains
     mount ::API::Pipelines
     mount ::API::PipelineSchedules
+    mount ::API::ProjectClusters
     mount ::API::ProjectExport
     mount ::API::ProjectImport
     mount ::API::ProjectHooks

lib/api/entities.rb

@@ -1516,5 +1516,38 @@ module API
       expose :from_content
       expose :to_content
     end
+
+    module Platform
+      class Kubernetes < Grape::Entity
+        expose :api_url
+        expose :namespace
+        expose :authorization_type
+        expose :ca_cert
+      end
+    end
+
+    module Provider
+      class Gcp < Grape::Entity
+        expose :cluster_id
+        expose :status_name
+        expose :gcp_project_id
+        expose :zone
+        expose :machine_type
+        expose :num_nodes
+        expose :endpoint
+      end
+    end
+
+    class Cluster < Grape::Entity
+      expose :id, :name, :created_at
+      expose :provider_type, :platform_type, :environment_scope, :cluster_type
+      expose :user, using: Entities::UserBasic
+      expose :platform_kubernetes, using: Entities::Platform::Kubernetes
+      expose :provider_gcp, using: Entities::Provider::Gcp
+    end
+
+    class ClusterProject < Cluster
+      expose :project, using: Entities::BasicProjectDetails
+    end
   end
 end

lib/api/project_clusters.rb

+# frozen_string_literal: true
+
+module API
+  class ProjectClusters < Grape::API
+    include PaginationParams
+
+    before { authenticate! }
+
+    # EE::API::ProjectClusters will
+    # override these methods
+    helpers do
+      params :create_params_ee do
+      end
+
+      params :update_params_ee do
+      end
+    end
+
+    params do
+      requires :id, type: String, desc: 'The ID of the project'
+    end
+    resource :projects, requirements: API::NAMESPACE_OR_PROJECT_REQUIREMENTS do
+      desc 'Get all clusters from the project' do
+        detail 'This feature was introduced in GitLab 11.7.'
+        success Entities::Cluster
+      end
+      params do
+        use :pagination
+      end
+      get ':id/clusters' do
+        authorize! :read_cluster, user_project
+
+        present paginate(clusters_for_current_user), with: Entities::Cluster
+      end
+
+      desc 'Get specific cluster for the project' do
+        detail 'This feature was introduced in GitLab 11.7.'
+        success Entities::ClusterProject
+      end
+      params do
+        requires :cluster_id, type: Integer, desc: 'The cluster ID'
+      end
+      get ':id/clusters/:cluster_id' do
+        authorize! :read_cluster, cluster
+
+        present cluster, with: Entities::ClusterProject
+      end
+
+      desc 'Adds an existing cluster' do
+        detail 'This feature was introduced in GitLab 11.7.'
+        success Entities::ClusterProject
+      end
+      params do
+        requires :name, type: String, desc: 'Cluster name'
+        optional :enabled, type: Boolean, default: true, desc: 'Determines if cluster is active or not, defaults to true'
+        requires :platform_kubernetes_attributes, type: Hash, desc: %q(Platform Kubernetes data) do
+          requires :api_url, type: String, allow_blank: false, desc: 'URL to access the Kubernetes API'
+          requires :token, type: String, desc: 'Token to authenticate against Kubernetes'
+          optional :ca_cert, type: String, desc: 'TLS certificate (needed if API is using a self-signed TLS certificate)'
+          optional :namespace, type: String, desc: 'Unique namespace related to Project'
+          optional :authorization_type, type: String, values: Clusters::Platforms::Kubernetes.authorization_types.keys, default: 'rbac', desc: 'Cluster authorization type, defaults to RBAC'
+        end
+        use :create_params_ee
+      end
+      post ':id/clusters/user' do
+        authorize! :create_cluster, user_project
+
+        user_cluster = ::Clusters::CreateService
+          .new(current_user, create_cluster_user_params)
+          .execute
+
+        if user_cluster.persisted?
+          present user_cluster, with: Entities::ClusterProject
+        else
+          render_validation_error!(user_cluster)
+        end
+      end
+
+      desc 'Update an existing cluster' do
+        detail 'This feature was introduced in GitLab 11.7.'
+        success Entities::ClusterProject
+      end
+      params do
+        requires :cluster_id, type: Integer, desc: 'The cluster ID'
+        optional :name, type: String, desc: 'Cluster name'
+        optional :platform_kubernetes_attributes, type: Hash, desc: %q(Platform Kubernetes data) do
+          optional :api_url, type: String, desc: 'URL to access the Kubernetes API'
+          optional :token, type: String, desc: 'Token to authenticate against Kubernetes'
+          optional :ca_cert, type: String, desc: 'TLS certificate (needed if API is using a self-signed TLS certificate)'
+          optional :namespace, type: String, desc: 'Unique namespace related to Project'
+        end
+        use :update_params_ee
+      end
+      put ':id/clusters/:cluster_id' do
+        authorize! :update_cluster, cluster
+
+        update_service = Clusters::UpdateService.new(current_user, update_cluster_params)
+
+        if update_service.execute(cluster)
+          present cluster, with: Entities::ClusterProject
+        else
+          render_validation_error!(cluster)
+        end
+      end
+
+      desc 'Remove a cluster' do
+        detail 'This feature was introduced in GitLab 11.7.'
+        success Entities::ClusterProject
+      end
+      params do
+        requires :cluster_id, type: Integer, desc: 'The Cluster ID'
+      end
+      delete ':id/clusters/:cluster_id' do
+        authorize! :admin_cluster, cluster
+
+        destroy_conditionally!(cluster)
+      end
+    end
+
+    helpers do
+      def clusters_for_current_user
+        @clusters_for_current_user ||= ClustersFinder.new(user_project, current_user, :all).execute
+      end
+
+      def cluster
+        @cluster ||= clusters_for_current_user.find(params[:cluster_id])
+      end
+
+      def create_cluster_user_params
+        declared_params.merge({
+          provider_type: :user,
+          platform_type: :kubernetes,
+          clusterable: user_project
+        })
+      end
+
+      def update_cluster_params
+        declared_params(include_missing: false).without(:cluster_id)
+      end
+    end
+  end
+end