fix: Don't retry more often than endpoints available (#390)

jobs/gorouter/spec

@@ -197,8 +197,9 @@ properties:
   router.backends.max_attempts:
     description: |
       Maximum number of attempts on failing requests against backend routes.
+      The number of attempts per request is limited by the number of endpoints on the route, regardless of this setting.
       This includes CF apps and route-registrar endpoints.
-      A value of 0 implies indefinite retries, i.e. retry until success or endpoint list is exhausted.
+      The minimum value for this setting is 1. This prevents gorouter from getting blocked by indefinite retries.
     default: 3
   router.backends.ca:
     description: Certificate authority that was used to sign certificates for TLS-registered backends. In PEM format.

jobs/gorouter/templates/gorouter.yml.erb

@@ -275,8 +275,8 @@ end
 backend_attempts = 3
 if_p('router.backends.max_attempts') { |val| backend_attempts = val }
 
-if (backend_attempts < 0 )
-  raise 'router.backends.max_attempts cannot be negative'
+if (backend_attempts < 1 )
+  raise 'router.backends.max_attempts must maintain a minimum value of 1'
 end
 
 backends = {

spec/gorouter_templates_spec.rb

@@ -673,16 +673,16 @@
           before do
             deployment_manifest_fragment['router']['backends']['max_attempts'] = 0
           end
-          it 'should configure the property with indefinite retries' do
-            expect(parsed_yaml['backends']['max_attempts']).to eq(0)
+          it 'should error' do
+            expect { raise parsed_yaml }.to raise_error(RuntimeError, 'router.backends.max_attempts must maintain a minimum value of 1')
           end
         end
         context 'when max_attempts is negative' do
           before do
             deployment_manifest_fragment['router']['backends']['max_attempts'] = -1
           end
           it 'should error' do
-            expect { raise parsed_yaml }.to raise_error(RuntimeError, 'router.backends.max_attempts cannot be negative')
+            expect { raise parsed_yaml }.to raise_error(RuntimeError, 'router.backends.max_attempts must maintain a minimum value of 1')
           end
         end
         context 'when both cert_chain and private_key are provided' do