Add GOGC and GOMEMLIMIT properties to BBS job

jobs/bbs/spec

@@ -186,6 +186,11 @@ properties:
     description: Maximum number of files (including sockets) the BBS process may have open.
     default: 100000
 
+  diego.bbs.gogc:
+    description: "Value for the GOGC environment variable controlling Go GC trigger threshold. Accepts an integer percentage (e.g. 100 means GC triggers when heap doubles, 200 when it triples) or 'off' to disable percentage-based GC triggering. When used with gomemlimit, setting this to 'off' lets the memory limit alone govern GC pacing, which reduces GC-induced latency spikes under high load."
+  diego.bbs.gomemlimit:
+    description: "Value for the GOMEMLIMIT environment variable setting a soft memory limit for the Go runtime (e.g. '8GiB'). Valid units: B, KiB, MiB, GiB, TiB. When set, the runtime paces garbage collection to stay under this limit. Recommended to set alongside gogc='off' for latency-sensitive workloads with sufficient available memory."
+
   logging.max_data_string_length:
     description: "Length in bytes above which logged strings will be truncated. If set to 0, turns off truncation."
     default: 640

jobs/bbs/templates/bpm.yml.erb

@@ -13,3 +13,18 @@ processes:
     end
     %>
     open_files: <%= p('limits.open_files') %>
+<%
+  gogc = nil
+  gomemlimit = nil
+  if_p('diego.bbs.gogc') { |v| gogc = v }
+  if_p('diego.bbs.gomemlimit') { |v| gomemlimit = v }
+%>
+<% if gogc || gomemlimit %>
+  env:
+  <% if gogc %>
+    GOGC: '<%= gogc %>'
+  <% end %>
+  <% if gomemlimit %>
+    GOMEMLIMIT: '<%= gomemlimit %>'
+  <% end %>
+<% end %>

spec/bbs_template_spec.rb

@@ -241,4 +241,120 @@
       end
     end
   end
+
+  describe 'bpm.yml.erb' do
+    let(:template) { job.template('config/bpm.yml') }
+
+    let(:deployment_manifest_fragment) do
+      {
+        'diego' => {
+          'bbs' => {
+            'ca_cert' => 'CA CERT',
+            'server_cert' => 'SERVER CERT',
+            'server_key' => 'SERVER KEY',
+            'active_key_label' => 'ACTIVE KEY',
+            'encryption_keys' => [{ 'label' => 'KEY', 'passphrase' => 'PASS' }],
+            'sql' => {
+              'db_host' => 'localhost',
+              'db_port' => 3306,
+              'db_schema' => 'diego',
+              'db_username' => 'diego',
+              'db_password' => 'password',
+              'db_driver' => 'mysql'
+            }
+          }
+        },
+        'limits' => { 'open_files' => 100_000 }
+      }
+    end
+
+    let(:rendered_template) { template.render(deployment_manifest_fragment) }
+    let(:rendered_yaml) { YAML.safe_load(rendered_template) }
+    let(:process) { rendered_yaml['processes'][0] }
+
+    describe 'process configuration' do
+      it 'configures the bbs process with correct executable and args' do
+        expect(process['name']).to eq('bbs')
+        expect(process['executable']).to eq('/var/vcap/packages/bbs/bin/bbs')
+        expect(process['args']).to eq(['-config=/var/vcap/jobs/bbs/config/bbs.json'])
+      end
+
+      it 'configures the pre_start hook' do
+        expect(process['hooks']['pre_start']).to eq('/var/vcap/jobs/bbs/bin/bpm-pre-start')
+      end
+    end
+
+    describe 'limits.open_files' do
+      it 'sets open_files from the property' do
+        expect(process['limits']['open_files']).to eq(100_000)
+      end
+
+      it 'fails when open_files is not a positive integer' do
+        deployment_manifest_fragment['limits']['open_files'] = -1
+        expect { rendered_template }.to raise_error(/limits.open_files must be a positive integer/)
+      end
+
+      it 'fails when open_files is zero' do
+        deployment_manifest_fragment['limits']['open_files'] = 0
+        expect { rendered_template }.to raise_error(/limits.open_files must be a positive integer/)
+      end
+
+      it 'fails when open_files is not an integer' do
+        deployment_manifest_fragment['limits']['open_files'] = 'abc'
+        expect { rendered_template }.to raise_error(/limits.open_files must be a positive integer/)
+      end
+    end
+
+    describe 'GC environment variables' do
+      context 'when no GC properties are set' do
+        it 'does not include an env section' do
+          expect(process).not_to have_key('env')
+        end
+      end
+
+      context 'when only diego.bbs.gogc is set' do
+        before do
+          deployment_manifest_fragment['diego']['bbs']['gogc'] = 'off'
+        end
+
+        it 'includes env with GOGC only' do
+          expect(process['env']['GOGC']).to eq('off')
+          expect(process['env']).not_to have_key('GOMEMLIMIT')
+        end
+      end
+
+      context 'when only diego.bbs.gomemlimit is set' do
+        before do
+          deployment_manifest_fragment['diego']['bbs']['gomemlimit'] = '8GiB'
+        end
+
+        it 'includes env with GOMEMLIMIT only' do
+          expect(process['env']['GOMEMLIMIT']).to eq('8GiB')
+          expect(process['env']).not_to have_key('GOGC')
+        end
+      end
+
+      context 'when both diego.bbs.gogc and diego.bbs.gomemlimit are set' do
+        before do
+          deployment_manifest_fragment['diego']['bbs']['gogc'] = 'off'
+          deployment_manifest_fragment['diego']['bbs']['gomemlimit'] = '8GiB'
+        end
+
+        it 'includes env with both GOGC and GOMEMLIMIT' do
+          expect(process['env']['GOGC']).to eq('off')
+          expect(process['env']['GOMEMLIMIT']).to eq('8GiB')
+        end
+      end
+
+      context 'when gogc is an integer value' do
+        before do
+          deployment_manifest_fragment['diego']['bbs']['gogc'] = 200
+        end
+
+        it 'renders the integer as a string in the env' do
+          expect(process['env']['GOGC']).to eq('200')
+        end
+      end
+    end
+  end
 end