New CEL based sampler with declarative config support

Author: dol

samplers/README.md

@@ -5,14 +5,15 @@
 The following samplers support [declarative configuration](https://opentelemetry.io/docs/languages/java/configuration/#declarative-configuration):
 
 * `RuleBasedRoutingSampler`
+* `CelBasedSampler`
 
 To use:
 
 * Add a dependency on `io.opentelemetry:opentelemetry-sdk-extension-incubator:<version>`
 * Follow the [instructions](https://github.com/open-telemetry/opentelemetry-java/blob/main/sdk-extensions/incubator/README.md#file-configuration) to configure OpenTelemetry with declarative configuration.
-* Configure the `.tracer_provider.sampler` to include the `rule_based_routing` sampler.
+* Configure the `.tracer_provider.sampler` to include the `rule_based_routing` or `cel_based` sampler.
 
-NOTE: Not yet available for use with the OTEL java agent, but should be in the near future. Please check back for updates.
+## RuleBasedRoutingSampler
 
 Schema for `rule_based_routing` sampler:
 
@@ -59,6 +60,66 @@ tracer_provider:
               pattern: /actuator.*
 ```
 
+## CelBasedSampler
+
+The `CelBasedSampler` uses [Common Expression Language (CEL)](https://github.com/google/cel-spec) to create advanced sampling rules based on span attributes. CEL provides a powerful, yet simple expression language that allows you to create complex matching conditions.
+
+To use:
+
+* Add a dependency on `io.opentelemetry:opentelemetry-sdk-extension-incubator:<version>`
+* Follow the [instructions](https://github.com/open-telemetry/opentelemetry-java/blob/main/sdk-extensions/incubator/README.md#file-configuration) to configure OpenTelemetry with declarative configuration.
+* Configure the `.tracer_provider.sampler` to include the `cel_based` sampler.
+
+Schema for `cel_based` sampler:
+
+```yaml
+# The fallback sampler to use if no expressions match.
+fallback_sampler:
+  always_on:
+# List of CEL expressions to evaluate. Expressions are evaluated in order.
+expressions:
+  # The action to take when the expression evaluates to true. Must be one of: DROP, RECORD_AND_SAMPLE.
+  - action: DROP
+    # The CEL expression to evaluate. Must return a boolean.
+    expression: attribute['url.path'].startsWith('/actuator')
+  - action: RECORD_AND_SAMPLE
+    expression: attribute['http.method'] == 'GET' && attribute['http.status_code'] < 400
+```
+
+Available variables in CEL expressions:
+
+* `name` (string): The span name
+* `spanKind` (string): The span kind (e.g., "SERVER", "CLIENT")
+* `attribute` (map): A map of span attributes
+
+Example of using `cel_based` sampler as the root sampler in `parent_based` sampler configuration:
+
+```yaml
+tracer_provider:
+  sampler:
+    parent_based:
+      root:
+        cel_based:
+          fallback_sampler:
+            always_on:
+          expressions:
+            # Drop health check endpoints
+            - action: DROP
+              expression: spanKind == 'SERVER' && attribute['url.path'].startsWith('/health')
+            # Drop actuator endpoints
+            - action: DROP
+              expression: spanKind == 'SERVER' && attribute['url.path'].startsWith('/actuator')
+            # Sample only HTTP GET requests with successful responses
+            - action: RECORD_AND_SAMPLE
+              expression: spanKind == 'SERVER' && attribute['http.method'] == 'GET' && attribute['http.status_code'] < 400
+            # Selectively sample based on span name
+            - action: RECORD_AND_SAMPLE
+              expression: name.contains('checkout') || name.contains('payment')
+            # Drop spans with specific name patterns
+            - action: DROP
+              expression: name.matches('.*internal.*') && spanKind == 'INTERNAL'
+```
+
 ## Component owners
 
 - [Jack Berg](https://github.com/jack-berg), New Relic

samplers/build.gradle.kts

@@ -9,6 +9,8 @@ otelJava.moduleName.set("io.opentelemetry.contrib.sampler")
 dependencies {
   api("io.opentelemetry:opentelemetry-sdk")
 
+  implementation("dev.cel:cel:0.9.0")
+
   compileOnly("io.opentelemetry:opentelemetry-sdk-extension-autoconfigure-spi")
   compileOnly("io.opentelemetry:opentelemetry-api-incubator")
   compileOnly("io.opentelemetry:opentelemetry-sdk-extension-incubator")

samplers/src/main/java/io/opentelemetry/contrib/sampler/CelBasedSampler.java

@@ -0,0 +1,142 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.contrib.sampler;
+
+import static java.util.Objects.requireNonNull;
+
+import dev.cel.common.types.SimpleType;
+import dev.cel.compiler.CelCompiler;
+import dev.cel.compiler.CelCompilerFactory;
+import dev.cel.runtime.CelEvaluationException;
+import dev.cel.runtime.CelRuntime;
+import dev.cel.runtime.CelRuntimeFactory;
+import io.opentelemetry.api.common.Attributes;
+import io.opentelemetry.api.trace.SpanBuilder;
+import io.opentelemetry.api.trace.SpanKind;
+import io.opentelemetry.context.Context;
+import io.opentelemetry.sdk.trace.data.LinkData;
+import io.opentelemetry.sdk.trace.samplers.Sampler;
+import io.opentelemetry.sdk.trace.samplers.SamplingResult;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+import java.util.regex.Pattern;
+
+/**
+ * This sampler accepts a list of {@link CelBasedSamplingExpression}s and tries to match every
+ * proposed span against those rules. Every rule describes a span's attribute, a pattern against
+ * which to match attribute's value, and a sampler that will make a decision about given span if
+ * match was successful.
+ *
+ * <p>Matching is performed by {@link Pattern}.
+ *
+ * <p>Provided span kind is checked first and if differs from the one given to {@link
+ * #builder(Sampler)}, the default fallback sampler will make a decision.
+ *
+ * <p>Note that only attributes that were set on {@link SpanBuilder} will be taken into account,
+ * attributes set after the span has been started are not used
+ *
+ * <p>If none of the rules matched, the default fallback sampler will make a decision.
+ */
+public final class CelBasedSampler implements Sampler {
+
+  private static final Logger logger = Logger.getLogger(CelBasedSampler.class.getName());
+
+  private static final CelCompiler celCompiler =
+      CelCompilerFactory.standardCelCompilerBuilder()
+          .addVar("name", SimpleType.STRING) // Span name
+          .addVar("spanKind", SimpleType.STRING) // Span kind as string
+          .addVar("attribute", SimpleType.DYN) // Attributes as a map
+          .setResultType(SimpleType.BOOL) // Expression must return boolean
+          .build();
+  final CelRuntime celRuntime;
+
+  private final Sampler fallback;
+  private final List<CelBasedSamplingExpression> expressions;
+
+  public CelBasedSampler(Sampler fallback, List<CelBasedSamplingExpression> expressions) {
+    this.fallback = fallback;
+    this.expressions = expressions;
+    this.celRuntime = CelRuntimeFactory.standardCelRuntimeBuilder().build();
+  }
+
+  public static CelBasedSamplerBuilder builder(Sampler fallback) {
+    return new CelBasedSamplerBuilder(
+        requireNonNull(fallback, "fallback sampler must not be null"), celCompiler);
+  }
+
+  @Override
+  public SamplingResult shouldSample(
+      Context parentContext,
+      String traceId,
+      String name,
+      SpanKind spanKind,
+      Attributes attributes,
+      List<LinkData> parentLinks) {
+
+    // Prepare the evaluation context with span data
+    Map<String, Object> evaluationContext = new HashMap<>();
+    evaluationContext.put("name", name);
+    evaluationContext.put("spanKind", spanKind.name());
+    evaluationContext.put("attribute", convertAttributesToMap(attributes));
+
+    for (CelBasedSamplingExpression expression : expressions) {
+      try {
+        CelRuntime.Program program = celRuntime.createProgram(expression.abstractSyntaxTree);
+        Object result = program.eval(evaluationContext);
+        // Happy path: Perform sampling based on the boolean result
+        if (result instanceof Boolean && ((Boolean) result)) {
+          return expression.delegate.shouldSample(
+              parentContext, traceId, name, spanKind, attributes, parentLinks);
+        }
+        // If result is not boolean, treat as false
+        logger.log(
+            Level.FINE,
+            "Expression '" + expression.expression + "' returned non-boolean result: " + result);
+      } catch (CelEvaluationException e) {
+        logger.log(
+            Level.FINE,
+            "Expression '" + expression.expression + "' evaluation error: " + e.getMessage());
+      }
+    }
+
+    return fallback.shouldSample(parentContext, traceId, name, spanKind, attributes, parentLinks);
+  }
+
+  /** Convert OpenTelemetry Attributes to a Map that CEL can work with */
+  private static Map<String, Object> convertAttributesToMap(Attributes attributes) {
+    Map<String, Object> map = new HashMap<>();
+    attributes.forEach(
+        (key, value) -> {
+          // Convert attribute values to appropriate types
+          if (value instanceof String) {
+            map.put(key.getKey(), value);
+          } else if (value instanceof Long) {
+            map.put(key.getKey(), value);
+          } else if (value instanceof Double) {
+            map.put(key.getKey(), value);
+          } else if (value instanceof Boolean) {
+            map.put(key.getKey(), value);
+          } else {
+            // For other types, convert to string
+            map.put(key.getKey(), value.toString());
+          }
+        });
+    return map;
+  }
+
+  @Override
+  public String getDescription() {
+    return "CelBasedSampler{" + "fallback=" + fallback + ", expressions=" + expressions + '}';
+  }
+
+  @Override
+  public String toString() {
+    return getDescription();
+  }
+}

samplers/src/main/java/io/opentelemetry/contrib/sampler/CelBasedSamplerBuilder.java

@@ -0,0 +1,69 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.contrib.sampler;
+
+import static java.util.Objects.requireNonNull;
+
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
+import dev.cel.common.CelAbstractSyntaxTree;
+import dev.cel.common.CelValidationException;
+import dev.cel.compiler.CelCompiler;
+import io.opentelemetry.api.common.AttributeKey;
+import io.opentelemetry.sdk.trace.samplers.Sampler;
+import java.util.ArrayList;
+import java.util.List;
+
+public final class CelBasedSamplerBuilder {
+  private final CelCompiler celCompiler;
+  private final List<CelBasedSamplingExpression> expressions = new ArrayList<>();
+  private final Sampler defaultDelegate;
+
+  CelBasedSamplerBuilder(Sampler defaultDelegate, CelCompiler celCompiler) {
+    this.defaultDelegate = defaultDelegate;
+    this.celCompiler = celCompiler;
+  }
+
+  /**
+   * Use the provided sampler when the value of the provided {@link AttributeKey} matches the
+   * provided pattern.
+   */
+  @CanIgnoreReturnValue
+  public CelBasedSamplerBuilder customize(Sampler sampler, String expression)
+      throws CelValidationException {
+
+    CelAbstractSyntaxTree abstractSyntaxTree = celCompiler.compile(expression).getAst();
+
+    expressions.add(
+        new CelBasedSamplingExpression(
+            requireNonNull(sampler, "sampler must not be null"),
+            requireNonNull(expression, "expression must not be null"),
+            requireNonNull(abstractSyntaxTree, "abstractSyntaxTree must not be null")));
+    return this;
+  }
+
+  /**
+   * Drop all spans when the value of the provided {@link AttributeKey} matches the provided
+   * pattern.
+   */
+  @CanIgnoreReturnValue
+  public CelBasedSamplerBuilder drop(String expression) throws CelValidationException {
+    return customize(Sampler.alwaysOff(), expression);
+  }
+
+  /**
+   * Record and sample all spans when the value of the provided {@link AttributeKey} matches the
+   * provided pattern.
+   */
+  @CanIgnoreReturnValue
+  public CelBasedSamplerBuilder recordAndSample(String expression) throws CelValidationException {
+    return customize(Sampler.alwaysOn(), expression);
+  }
+
+  /** Build the sampler based on the rules provided. */
+  public CelBasedSampler build() {
+    return new CelBasedSampler(defaultDelegate, expressions);
+  }
+}

samplers/src/main/java/io/opentelemetry/contrib/sampler/CelBasedSamplingExpression.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.contrib.sampler;
+
+import dev.cel.common.CelAbstractSyntaxTree;
+import io.opentelemetry.sdk.trace.samplers.Sampler;
+import java.util.Objects;
+import javax.annotation.Nullable;
+
+public class CelBasedSamplingExpression {
+  final Sampler delegate;
+  final String expression;
+  final CelAbstractSyntaxTree abstractSyntaxTree;
+
+  CelBasedSamplingExpression(
+      Sampler delegate, String expression, CelAbstractSyntaxTree abstractSyntaxTree) {
+    this.delegate = delegate;
+    this.expression = expression;
+    this.abstractSyntaxTree = abstractSyntaxTree;
+  }
+
+  @Override
+  public String toString() {
+    return "CelBasedSamplingExpression{"
+        + "delegate="
+        + delegate
+        + ", expression='"
+        + expression
+        + '}';
+  }
+
+  @Override
+  public boolean equals(@Nullable Object o) {
+    if (this == o) {
+      return true;
+    }
+    if (!(o instanceof CelBasedSamplingExpression)) {
+      return false;
+    }
+    CelBasedSamplingExpression that = (CelBasedSamplingExpression) o;
+    return Objects.equals(delegate, that.delegate)
+        && Objects.equals(expression, that.expression)
+        && Objects.equals(abstractSyntaxTree, that.abstractSyntaxTree);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(delegate, expression, abstractSyntaxTree);
+  }
+}