Retry fetching Kubernetes Secret token

Since Kubernetes is creating the Secret and token asynchronously it is
necessary that we implement some delay or retrying logic to avoid a race
condition where we fetch a Secret before the token is even set. There
does not appear to be any way for us to force it to be set with any
synchronous API call so retrying seems to be the only option.

app/services/clusters/gcp/kubernetes/fetch_kubernetes_token_service.rb

@@ -4,17 +4,30 @@ module Clusters
   module Gcp
     module Kubernetes
       class FetchKubernetesTokenService
+        DEFAULT_TOKEN_RETRY_DELAY = 5.seconds
+        TOKEN_RETRY_LIMIT = 5
+
         attr_reader :kubeclient, :service_account_token_name, :namespace
 
-        def initialize(kubeclient, service_account_token_name, namespace)
+        def initialize(kubeclient, service_account_token_name, namespace, token_retry_delay: DEFAULT_TOKEN_RETRY_DELAY)
           @kubeclient = kubeclient
           @service_account_token_name = service_account_token_name
           @namespace = namespace
+          @token_retry_delay = token_retry_delay
         end
 
         def execute
-          token_base64 = get_secret&.dig('data', 'token')
-          Base64.decode64(token_base64) if token_base64
+          # Kubernetes will create the Secret and set the token asynchronously
+          # so it is necessary to retry
+          # https://kubernetes.io/docs/reference/access-authn-authz/service-accounts-admin/#token-controller
+          TOKEN_RETRY_LIMIT.times do
+            token_base64 = get_secret&.dig('data', 'token')
+            return Base64.decode64(token_base64) if token_base64
+
+            sleep @token_retry_delay
+          end
+
+          nil
         end
 
         private

changelogs/unreleased/63507-fix-race-condition-fetching-token.yml

+---
+title: Retry fetching Kubernetes Secret#token (#63507)
+merge_request: 29922
+author:
+type: fixed

spec/services/clusters/gcp/kubernetes/fetch_kubernetes_token_service_spec.rb

@@ -17,7 +17,7 @@ describe Clusters::Gcp::Kubernetes::FetchKubernetesTokenService do
       )
     end
 
-    subject { described_class.new(kubeclient, service_account_token_name, namespace).execute }
+    subject { described_class.new(kubeclient, service_account_token_name, namespace, token_retry_delay: 0).execute }
 
     before do
       stub_kubeclient_discover(api_url)
@@ -26,8 +26,7 @@ describe Clusters::Gcp::Kubernetes::FetchKubernetesTokenService do
     context 'when params correct' do
       let(:decoded_token) { 'xxx.token.xxx' }
       let(:token) { Base64.encode64(decoded_token) }
-
-      context 'when gitlab-token exists' do
+      context 'when the secret exists' do
         before do
           stub_kubeclient_get_secret(
             api_url,
@@ -50,13 +49,62 @@ describe Clusters::Gcp::Kubernetes::FetchKubernetesTokenService do
         it { expect { subject }.to raise_error(Kubeclient::HttpError) }
       end
 
-      context 'when gitlab-token does not exist' do
+      context 'when the secret does not exist on the first try' do
+        before do
+          stub_kubeclient_get_secret_not_found_then_found(
+            api_url,
+            {
+              metadata_name: service_account_token_name,
+              namespace: namespace,
+              token: token
+            }
+          )
+        end
+
+        it 'retries and finds the token' do
+          expect(subject).to eq(decoded_token)
+        end
+      end
+
+      context 'when the secret permanently does not exist' do
         before do
           stub_kubeclient_get_secret_error(api_url, service_account_token_name, namespace: namespace, status: 404)
         end
 
         it { is_expected.to be_nil }
       end
+
+      context 'when the secret is missing a token on the first try' do
+        before do
+          stub_kubeclient_get_secret_missing_token_then_with_token(
+            api_url,
+            {
+              metadata_name: service_account_token_name,
+              namespace: namespace,
+              token: token
+            }
+          )
+        end
+
+        it 'retries and finds the token' do
+          expect(subject).to eq(decoded_token)
+        end
+      end
+
+      context 'when the secret is permanently missing a token' do
+        before do
+          stub_kubeclient_get_secret(
+            api_url,
+            {
+              metadata_name: service_account_token_name,
+              namespace: namespace,
+              token: nil
+            }
+          )
+        end
+
+        it { is_expected.to be_nil }
+      end
     end
   end
 end

spec/support/helpers/kubernetes_helpers.rb

@@ -104,6 +104,26 @@ module KubernetesHelpers
       .to_return(status: [status, "Internal Server Error"])
   end
 
+  def stub_kubeclient_get_secret_not_found_then_found(api_url, **options)
+    options[:metadata_name] ||= "default-token-1"
+    options[:namespace] ||= "default"
+
+    WebMock.stub_request(:get, api_url + "/api/v1/namespaces/#{options[:namespace]}/secrets/#{options[:metadata_name]}")
+      .to_return(status: [404, "Not Found"])
+      .then
+      .to_return(kube_response(kube_v1_secret_body(options)))
+  end
+
+  def stub_kubeclient_get_secret_missing_token_then_with_token(api_url, **options)
+    options[:metadata_name] ||= "default-token-1"
+    options[:namespace] ||= "default"
+
+    WebMock.stub_request(:get, api_url + "/api/v1/namespaces/#{options[:namespace]}/secrets/#{options[:metadata_name]}")
+      .to_return(kube_response(kube_v1_secret_body(options.merge(token: nil))))
+      .then
+      .to_return(kube_response(kube_v1_secret_body(options)))
+  end
+
   def stub_kubeclient_get_service_account(api_url, name, namespace: 'default')
     WebMock.stub_request(:get, api_url + "/api/v1/namespaces/#{namespace}/serviceaccounts/#{name}")
       .to_return(kube_response({}))
@@ -184,11 +204,11 @@ module KubernetesHelpers
       "kind" => "SecretList",
       "apiVersion": "v1",
       "metadata": {
-        "name": options[:metadata_name] || "default-token-1",
+        "name": options.fetch(:metadata_name, "default-token-1"),
         "namespace": "kube-system"
       },
       "data": {
-        "token": options[:token] || Base64.encode64('token-sample-123')
+        "token": options.fetch(:token, Base64.encode64('token-sample-123'))
       }
     }
   end