merge: #9274

9274: [Backport stable/8.0] feat(broker): add feature flag template r=pihme a=github-actions[bot]

# Description
Backport of #9257 to `stable/8.0`.

relates to #9254

Co-authored-by: pihme <pihme@users.noreply.github.com>

broker/pom.xml

@@ -227,6 +227,10 @@
       <groupId>uk.co.real-logic</groupId>
       <artifactId>sbe-tool</artifactId>
     </dependency>
+    <dependency>
+      <groupId>org.apache.commons</groupId>
+      <artifactId>commons-lang3</artifactId>
+    </dependency>
     <dependency>
       <groupId>io.camunda</groupId>
       <artifactId>zeebe-util</artifactId>

broker/src/main/java/io/camunda/zeebe/broker/system/configuration/ExperimentalCfg.java

@@ -30,6 +30,8 @@ public class ExperimentalCfg implements ConfigurationEntry {
   private QueryApiCfg queryApi = new QueryApiCfg();
   private ConsistencyCheckCfg consistencyChecks = new ConsistencyCheckCfg();
 
+  private FeatureFlagsCfg features = new FeatureFlagsCfg();
+
   @Override
   public void init(final BrokerCfg globalConfig, final String brokerBase) {
     rocksdb.init(globalConfig, brokerBase);
@@ -104,6 +106,14 @@ public void setConsistencyChecks(final ConsistencyCheckCfg consistencyChecks) {
     this.consistencyChecks = consistencyChecks;
   }
 
+  public FeatureFlagsCfg getFeatures() {
+    return features;
+  }
+
+  public void setFeatures(final FeatureFlagsCfg features) {
+    this.features = features;
+  }
+
   @Override
   public String toString() {
     return "ExperimentalCfg{"
@@ -121,6 +131,8 @@ public String toString() {
         + queryApi
         + ", consistencyChecks="
         + consistencyChecks
+        + ", features="
+        + features
         + '}';
   }
 }

broker/src/main/java/io/camunda/zeebe/broker/system/configuration/FeatureFlagsCfg.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright Camunda Services GmbH and/or licensed to Camunda Services GmbH under
+ * one or more contributor license agreements. See the NOTICE file distributed
+ * with this work for additional information regarding copyright ownership.
+ * Licensed under the Zeebe Community License 1.1. You may not use this file
+ * except in compliance with the Zeebe Community License 1.1.
+ */
+package io.camunda.zeebe.broker.system.configuration;
+
+import com.fasterxml.jackson.databind.annotation.JsonSerialize;
+import io.camunda.zeebe.util.FeatureFlags;
+import org.apache.commons.lang3.builder.ToStringBuilder;
+import org.apache.commons.lang3.builder.ToStringStyle;
+
+@JsonSerialize // this annotation seems to implicitly disable
+// SerializationFeature.FAIL_ON_EMPTY_BEANS
+public final class FeatureFlagsCfg {
+
+  // To add a new feature flag, read the comments in FeatureFlags
+
+  private static final FeatureFlags DEFAULT_SETTINGS = FeatureFlags.createDefault();
+  //
+  //  private boolean enableFoo = DEFAULT_SETTINGS.foo();
+  //
+  //  public boolean isEnableFoo() {
+  //    return enableFoo;
+  //  }
+  //
+  //  public void setEnableFoo(final boolean enableFoo) {
+  //    this.enableFoo = enableFoo;
+  //  }
+
+  FeatureFlags toFeatureFlags() {
+    return new FeatureFlags(/*enableFoo*/ );
+  }
+
+  @Override
+  public String toString() {
+    return ToStringBuilder.reflectionToString(this, ToStringStyle.SHORT_PREFIX_STYLE);
+  }
+}

util/pom.xml

@@ -81,6 +81,11 @@
       <artifactId>spring-boot-actuator-autoconfigure</artifactId>
     </dependency>
 
+    <dependency>
+      <groupId>org.apache.commons</groupId>
+      <artifactId>commons-lang3</artifactId>
+    </dependency>
+
     <dependency>
       <groupId>junit</groupId>
       <artifactId>junit</artifactId>

util/src/main/java/io/camunda/zeebe/util/FeatureFlags.java

@@ -0,0 +1,44 @@
+/*
+ * Copyright Camunda Services GmbH and/or licensed to Camunda Services GmbH under
+ * one or more contributor license agreements. See the NOTICE file distributed
+ * with this work for additional information regarding copyright ownership.
+ * Licensed under the Zeebe Community License 1.1. You may not use this file
+ * except in compliance with the Zeebe Community License 1.1.
+ */
+package io.camunda.zeebe.util;
+
+import org.apache.commons.lang3.builder.ToStringBuilder;
+import org.apache.commons.lang3.builder.ToStringStyle;
+
+public record FeatureFlags(/*boolean foo*/ ) {
+
+  /* To add a new feature toggle, please follow these steps:
+   *
+   * - add a record property to this class, and extend the test for this class
+   *
+   * - define the default value. When introducing a new feature flag the default
+   *   value should be 'false'. This way the feature is disabled by default
+   *   for all customers who do not change their configuration.
+   *   As we gain more confidence in the efficacy of the feature flag, the
+   *   default value can be set to 'true'
+   *
+   * - add a field, getter and setter to FeatureFlagsCfg
+   *
+   * - add a description of the feature flag to
+   *    - dist/src/main/config/broker.standalone.yaml.template
+   *    - dist/src/main/config/broker.yaml.template
+   *
+   * Be careful with parameter order in constructor calls!
+   */
+
+  //  protected static final boolean FOO_DEFAULT = false;
+  //
+  public static FeatureFlags createDefault() {
+    return new FeatureFlags(/*FOO_DEFAULT*/ );
+  }
+
+  @Override
+  public String toString() {
+    return ToStringBuilder.reflectionToString(this, ToStringStyle.SHORT_PREFIX_STYLE);
+  }
+}

util/src/test/java/io/camunda/zeebe/util/FeatureFlagsTest.java

@@ -0,0 +1,22 @@
+/*
+ * Copyright Camunda Services GmbH and/or licensed to Camunda Services GmbH under
+ * one or more contributor license agreements. See the NOTICE file distributed
+ * with this work for additional information regarding copyright ownership.
+ * Licensed under the Zeebe Community License 1.1. You may not use this file
+ * except in compliance with the Zeebe Community License 1.1.
+ */
+package io.camunda.zeebe.util;
+
+import org.junit.jupiter.api.Test;
+
+public class FeatureFlagsTest {
+
+  @Test
+  void testDefaultValues() {
+    // given
+    final var sut = FeatureFlags.createDefault();
+
+    // then
+    // assertThat(sut.foo()).isFalse();
+  }
+}