diff --git a/packages/grpc-js-xds/interop/xds-interop-client.ts b/packages/grpc-js-xds/interop/xds-interop-client.ts
index c3cb55d5..f70ed4ff 100644
--- a/packages/grpc-js-xds/interop/xds-interop-client.ts
+++ b/packages/grpc-js-xds/interop/xds-interop-client.ts
@@ -303,6 +303,8 @@ function main() {
       currentConfig.callTypes = call.request.types;
       currentConfig.metadata = callMetadata;
       currentConfig.timeoutSec = call.request.timeout_sec
+      console.log('Received new client configuration: ' + JSON.stringify(currentConfig, undefined, 2));
+      callback(null, {});
     }
   }
 
diff --git a/packages/grpc-js-xds/src/matcher.ts b/packages/grpc-js-xds/src/matcher.ts
new file mode 100644
index 00000000..a70cf5d6
--- /dev/null
+++ b/packages/grpc-js-xds/src/matcher.ts
@@ -0,0 +1,245 @@
+/*
+ * Copyright 2021 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { Metadata } from "@grpc/grpc-js";
+import { RE2 } from "re2-wasm";
+
+/**
+ * An object representing a predicate that determines whether a given
+ * combination of a methodName and metadata matches some internal conditions.
+ */
+export interface Matcher {
+  toString(): string;
+  apply(methodName: string, metadata: Metadata): boolean;
+}
+
+/**
+ * An object representing a predicate that determines whether a given string
+ * value matches some internal conditions.
+ */
+export interface ValueMatcher {
+  toString(): string;
+  apply(value: string): boolean;
+}
+
+export class ExactValueMatcher implements ValueMatcher {
+  constructor(private targetValue: string) {}
+
+  apply(value: string) {
+    return value === this.targetValue;
+  }
+
+  toString() {
+    return 'Exact(' + this.targetValue + ')';
+  }
+}
+
+export class SafeRegexValueMatcher implements ValueMatcher {
+  private targetRegexImpl: RE2;
+  constructor(targetRegex: string) {
+    this.targetRegexImpl = new RE2(`^${targetRegex}$`, 'u');
+  }
+
+  apply(value: string) {
+    return this.targetRegexImpl.test(value);
+  }
+
+  toString() {
+    return 'SafeRegex(' + this.targetRegexImpl.toString() + ')';
+  }
+}
+
+const numberRegex = new RE2(/^-?\d+$/u);
+
+export class RangeValueMatcher implements ValueMatcher {
+  constructor(private start: BigInt, private end: BigInt) {}
+
+  apply(value: string) {
+    if (!numberRegex.test(value)) {
+      return false;
+    }
+    const numberValue = BigInt(value);
+    return this.start <= numberValue && numberValue < this.end;
+  }
+
+  toString() {
+    return 'Range(' + this.start + ', ' + this.end + ')';
+  }
+}
+
+export class PresentValueMatcher implements ValueMatcher {
+  constructor() {}
+
+  apply(value: string) {
+    return true;
+  }
+
+  toString() {
+    return 'Present()';
+  }
+}
+
+export class PrefixValueMatcher implements ValueMatcher {
+  constructor(private prefix: string) {}
+
+  apply(value: string) {
+    return value.startsWith(this.prefix);
+  }
+
+  toString() {
+    return 'Prefix(' + this.prefix + ')';
+  }
+}
+
+export class SuffixValueMatcher implements ValueMatcher {
+  constructor(private suffix: string) {}
+
+  apply(value: string) {
+    return value.endsWith(this.suffix);
+  }
+
+  toString() {
+    return 'Suffix(' + this.suffix + ')';
+  }
+}
+
+export class RejectValueMatcher implements ValueMatcher {
+  constructor() {}
+
+  apply(value: string) {
+    return false;
+  }
+
+  toString() {
+    return 'Reject()';
+  }
+}
+
+export class HeaderMatcher implements Matcher {
+  constructor(private headerName: string, private valueMatcher: ValueMatcher, private invertMatch: boolean) {}
+
+  private applyHelper(methodName: string, metadata: Metadata) {
+    if (this.headerName.endsWith('-bin')) {
+      return false;
+    }
+    let value: string;
+    if (this.headerName === 'content-type') {
+      value = 'application/grpc';
+    } else {
+      const valueArray = metadata.get(this.headerName);
+      if (valueArray.length === 0) {
+        return false;
+      } else {
+        value = valueArray.join(',');
+      }
+    }
+    return this.valueMatcher.apply(value);
+  }
+
+  apply(methodName: string, metadata: Metadata) {
+    const result = this.applyHelper(methodName, metadata);
+    if (this.invertMatch) {
+      return !result;
+    } else {
+      return result;
+    }
+  }
+
+  toString() {
+    return 'HeaderMatch(' + this.headerName + ', ' + this.valueMatcher.toString() + ')';
+  }
+}
+
+export class PathPrefixValueMatcher {
+  constructor(private prefix: string, private caseInsensitive: boolean) {}
+
+  apply(value: string) {
+    if (this.caseInsensitive) {
+      return value.toLowerCase().startsWith(this.prefix.toLowerCase());
+    } else {
+      return value.startsWith(this.prefix);
+    }
+  }
+
+  toString() {
+    return 'Prefix(' + this.prefix + ', ' + this.caseInsensitive + ')';
+  }
+}
+
+export class PathExactValueMatcher {
+  constructor(private targetValue: string, private caseInsensitive: boolean) {}
+
+  apply(value: string) {
+    if (this.caseInsensitive) {
+      return value.toLowerCase().startsWith(this.targetValue.toLowerCase());
+    } else {
+      return value === this.targetValue;
+    }
+  }
+
+  toString() {
+    return 'Exact(' + this.targetValue + ', ' + this.caseInsensitive + ')';
+  }
+}
+
+export class PathSafeRegexValueMatcher {
+  private targetRegexImpl: RE2;
+  constructor(targetRegex: string, caseInsensitive: boolean) {
+    this.targetRegexImpl = new RE2(`^${targetRegex}$`, caseInsensitive ? 'iu' : 'u');
+  }
+
+  apply(value: string) {
+    return this.targetRegexImpl.test(value);
+  }
+
+  toString() {
+    return 'SafeRegex(' + this.targetRegexImpl.toString() + ')';
+  }
+}
+
+export interface Fraction {
+  numerator: number;
+  denominator: number;
+}
+
+function fractionToString(fraction: Fraction): string {
+  return `${fraction.numerator}/${fraction.denominator}`;
+}
+
+export class FullMatcher implements Matcher {
+  constructor(private pathMatcher: ValueMatcher, private headerMatchers: Matcher[], private fraction: Fraction | null) {}
+
+  apply(methodName: string, metadata: Metadata) {
+    if (!this.pathMatcher.apply(methodName)) {
+      return false;
+    }
+    if (!this.headerMatchers.every(matcher => matcher.apply(methodName, metadata))) {
+      return false;
+    }
+    if (this.fraction === null) {
+      return true;
+    } else {
+      const randomNumber = Math.random() * this.fraction.denominator;
+      return randomNumber < this.fraction.numerator;
+    }
+  }
+
+  toString() {
+    return `path: ${this.pathMatcher}
+    headers: ${this.headerMatchers.map(matcher => matcher.toString()).join('\n\t')}
+    fraction: ${this.fraction ? fractionToString(this.fraction): 'none'}`;
+  }
+}
\ No newline at end of file
diff --git a/packages/grpc-js-xds/src/resolver-xds.ts b/packages/grpc-js-xds/src/resolver-xds.ts
index 99bbd58c..0fbb3030 100644
--- a/packages/grpc-js-xds/src/resolver-xds.ts
+++ b/packages/grpc-js-xds/src/resolver-xds.ts
@@ -38,6 +38,8 @@ import { HeaderMatcher__Output } from './generated/envoy/api/v2/route/HeaderMatc
 import ConfigSelector = experimental.ConfigSelector;
 import LoadBalancingConfig = experimental.LoadBalancingConfig;
 import { XdsClusterManagerLoadBalancingConfig } from './load-balancer-xds-cluster-manager';
+import { ExactValueMatcher, Fraction, FullMatcher, HeaderMatcher, Matcher, PathExactValueMatcher, PathPrefixValueMatcher, PathSafeRegexValueMatcher, PrefixValueMatcher, PresentValueMatcher, RangeValueMatcher, RejectValueMatcher, SafeRegexValueMatcher, SuffixValueMatcher, ValueMatcher } from './matcher';
+import { RouteAction, SingleClusterRouteAction, WeightedCluster, WeightedClusterRouteAction } from './route-action';
 
 const TRACER_NAME = 'xds_resolver';
 
@@ -119,68 +121,35 @@ function findVirtualHostForDomain(virutalHostList: VirtualHost__Output[], domain
   return targetVhost;
 }
 
-interface Matcher {
-  (methodName: string, metadata: Metadata): boolean;
-}
-
 const numberRegex = new RE2(/^-?\d+$/u);
 
 function getPredicateForHeaderMatcher(headerMatch: HeaderMatcher__Output): Matcher {
-  let valueChecker: (value: string) => boolean;
+  let valueChecker: ValueMatcher;
   switch (headerMatch.header_match_specifier) {
     case 'exact_match':
-      valueChecker = value => value === headerMatch.exact_match;
+      valueChecker = new ExactValueMatcher(headerMatch.exact_match!);
       break;
     case 'safe_regex_match':
-      const regex = new RE2(`^${headerMatch.safe_regex_match}$`, 'u');
-      valueChecker = value => regex.test(value);
+      valueChecker = new SafeRegexValueMatcher(headerMatch.safe_regex_match!.regex);
       break;
     case 'range_match':
       const start = BigInt(headerMatch.range_match!.start);
       const end = BigInt(headerMatch.range_match!.end);
-      valueChecker = value => {
-        if (!numberRegex.test(value)) {
-          return false;
-        }
-        const numberValue = BigInt(value);
-        return start <= numberValue && numberValue < end;
-      }
+      valueChecker = new RangeValueMatcher(start, end);
       break;
     case 'present_match':
-      valueChecker = value => true;
+      valueChecker = new PresentValueMatcher();
       break;
     case 'prefix_match':
-      valueChecker = value => value.startsWith(headerMatch.prefix_match!);
+      valueChecker = new PrefixValueMatcher(headerMatch.prefix_match!);
       break;
     case 'suffix_match':
-      valueChecker = value => value.endsWith(headerMatch.suffix_match!);
+      valueChecker = new SuffixValueMatcher(headerMatch.suffix_match!);
       break;
     default:
-      // Should be prevented by validation rules
-      return (methodName, metadata) => false;
-  }
-  const headerMatcher: Matcher = (methodName, metadata) => {
-    if (headerMatch.name.endsWith('-bin')) {
-      return false;
-    }
-    let value: string;
-    if (headerMatch.name === 'content-type') {
-      value = 'application/grpc';
-    } else {
-      const valueArray = metadata.get(headerMatch.name);
-      if (valueArray.length === 0) {
-        return false;
-      } else {
-        value = valueArray.join(',');
-      }
-    }
-    return valueChecker(value);
-  }
-  if (headerMatch.invert_match) {
-    return (methodName, metadata) => !headerMatcher(methodName, metadata);
-  } else {
-    return headerMatcher;
+      valueChecker = new RejectValueMatcher();
   }
+  return new HeaderMatcher(headerMatch.name, valueChecker, headerMatch.invert_match);
 }
 
 const RUNTIME_FRACTION_DENOMINATOR_VALUES = {
@@ -190,48 +159,32 @@ const RUNTIME_FRACTION_DENOMINATOR_VALUES = {
 }
 
 function getPredicateForMatcher(routeMatch: RouteMatch__Output): Matcher {
-  let pathMatcher: Matcher;
+  let pathMatcher: ValueMatcher;
+  const caseInsensitive = routeMatch.case_sensitive?.value === false;
   switch (routeMatch.path_specifier) {
     case 'prefix':
-      if (routeMatch.case_sensitive?.value === false) {
-        const prefix = routeMatch.prefix!.toLowerCase();
-        pathMatcher = (methodName, metadata) => (methodName.toLowerCase().startsWith(prefix));
-      } else {
-        const prefix = routeMatch.prefix!;
-        pathMatcher = (methodName, metadata) => (methodName.startsWith(prefix));
-      }
+      pathMatcher = new PathPrefixValueMatcher(routeMatch.prefix!, caseInsensitive);
       break;
     case 'path':
-      if (routeMatch.case_sensitive?.value === false) {
-        const path = routeMatch.path!.toLowerCase();
-        pathMatcher = (methodName, metadata) => (methodName.toLowerCase() === path);
-      } else {
-        const path = routeMatch.path!;
-        pathMatcher = (methodName, metadata) => (methodName === path);
-      }
+      pathMatcher = new PathExactValueMatcher(routeMatch.path!, caseInsensitive);
       break;
     case 'safe_regex':
-      const flags = routeMatch.case_sensitive?.value === false ? 'ui' : 'u';
-      const regex = new RE2(`^${routeMatch.safe_regex!.regex!}$`, flags);
-      pathMatcher = (methodName, metadata) => (regex.test(methodName));
+      pathMatcher = new PathSafeRegexValueMatcher(routeMatch.safe_regex!.regex, caseInsensitive);
       break;
     default:
-      // Should be prevented by validation rules
-      return (methodName, metadata) => false;
+      pathMatcher = new RejectValueMatcher();
   }
   const headerMatchers: Matcher[] = routeMatch.headers.map(getPredicateForHeaderMatcher);
-  let runtimeFractionHandler: () => boolean;
+  let runtimeFraction: Fraction | null;
   if (!routeMatch.runtime_fraction?.default_value) {
-    runtimeFractionHandler = () => true;
+    runtimeFraction = null;
   } else {
-    const numerator = routeMatch.runtime_fraction.default_value.numerator;
-    const denominator = RUNTIME_FRACTION_DENOMINATOR_VALUES[routeMatch.runtime_fraction.default_value.denominator];
-    runtimeFractionHandler = () => {
-      const randomNumber = Math.random() * denominator;
-      return randomNumber < numerator;
-    }
+    runtimeFraction = {
+      numerator: routeMatch.runtime_fraction.default_value.numerator,
+      denominator: RUNTIME_FRACTION_DENOMINATOR_VALUES[routeMatch.runtime_fraction.default_value.denominator]
+    };
   }
-  return (methodName, metadata) => pathMatcher(methodName, metadata) && headerMatchers.every(matcher => matcher(methodName, metadata)) && runtimeFractionHandler();
+  return new FullMatcher(pathMatcher, headerMatchers, runtimeFraction);
 }
 
 class XdsResolver implements Resolver {
@@ -340,38 +293,27 @@ class XdsResolver implements Resolver {
         this.reportResolutionError('No matching route found');
         return;
       }
+      trace('Received virtual host config ' + JSON.stringify(virtualHost, undefined, 2));
       const allConfigClusters = new Set<string>();
-      const matchList: {matcher: Matcher, action: () => string}[] = [];
+      const matchList: {matcher: Matcher, action: RouteAction}[] = [];
       for (const route of virtualHost.routes) {
-        let routeAction: () => string;
+        let routeAction: RouteAction;
         switch (route.route!.cluster_specifier) {
           case 'cluster_header':
             continue;
           case 'cluster':{
             const cluster = route.route!.cluster!;
             allConfigClusters.add(cluster);
-            routeAction = () => cluster;
+            routeAction = new SingleClusterRouteAction(cluster);
             break;
           }
           case 'weighted_clusters': {
-            let lastNumerator = 0;
-            // clusterChoices is essentially the weighted choices represented as a CDF
-            const clusterChoices: {cluster: string, numerator: number}[] = [];
+            const weightedClusters: WeightedCluster[] = [];
             for (const clusterWeight of route.route!.weighted_clusters!.clusters) {
               allConfigClusters.add(clusterWeight.name);
-              lastNumerator = lastNumerator + (clusterWeight.weight?.value ?? 0);
-              clusterChoices.push({cluster: clusterWeight.name, numerator: lastNumerator});
-            }
-            routeAction = () => {
-              const randomNumber = Math.random() * (route.route!.weighted_clusters!.total_weight?.value ?? 100);
-              for (const choice of clusterChoices) {
-                if (randomNumber < choice.numerator) {
-                  return choice.cluster;
-                }
-              }
-              // This should be prevented by the validation rules
-              return '';
+              weightedClusters.push({name: clusterWeight.name, weight: clusterWeight.weight?.value ?? 0});
             }
+            routeAction = new WeightedClusterRouteAction(weightedClusters, route.route!.weighted_clusters!.total_weight?.value ?? 100);
           }
         }
         const routeMatcher = getPredicateForMatcher(route.match!);
@@ -397,8 +339,8 @@ class XdsResolver implements Resolver {
       }
       const configSelector: ConfigSelector = (methodName, metadata) => {
         for (const {matcher, action} of matchList) {
-          if (matcher(methodName, metadata)) {
-            const clusterName = action();
+          if (matcher.apply(methodName, metadata)) {
+            const clusterName = action.getCluster();
             this.refCluster(clusterName);
             const onCommitted = () => {
               this.unrefCluster(clusterName);
@@ -418,6 +360,11 @@ class XdsResolver implements Resolver {
           status: status.UNAVAILABLE
         };
       };
+      trace('Created ConfigSelector with configuration:');
+      for (const {matcher, action} of matchList) {
+        trace(matcher.toString());
+        trace('=> ' + action.toString());
+      }
       const clusterConfigMap = new Map<string, {child_policy: LoadBalancingConfig[]}>();
       for (const clusterName of this.clusterRefcounts.keys()) {
         clusterConfigMap.set(clusterName, {child_policy: [new CdsLoadBalancingConfig(clusterName)]});
diff --git a/packages/grpc-js-xds/src/route-action.ts b/packages/grpc-js-xds/src/route-action.ts
new file mode 100644
index 00000000..4ba2b590
--- /dev/null
+++ b/packages/grpc-js-xds/src/route-action.ts
@@ -0,0 +1,72 @@
+/*
+ * Copyright 2021 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+export interface RouteAction {
+  toString(): string;
+  getCluster(): string;
+}
+
+export class SingleClusterRouteAction implements RouteAction {
+  constructor(private cluster: string) {}
+
+  getCluster() {
+    return this.cluster;
+  }
+
+  toString() {
+    return 'SingleCluster(' + this.cluster + ')';
+  }
+}
+
+export interface WeightedCluster {
+  name: string;
+  weight: number;
+}
+
+interface ClusterChoice {
+  name: string;
+  numerator: number;
+}
+
+export class WeightedClusterRouteAction implements RouteAction {
+  /**
+   * The weighted cluster choices represented as a CDF
+   */
+  private clusterChoices: ClusterChoice[];
+  constructor(private clusters: WeightedCluster[], private totalWeight: number) {
+    this.clusterChoices = [];
+    let lastNumerator = 0;
+    for (const clusterWeight of clusters) {
+      lastNumerator += clusterWeight.weight;
+      this.clusterChoices.push({name: clusterWeight.name, numerator: lastNumerator});
+    }
+  }
+
+  getCluster() {
+    const randomNumber = Math.random() * this.totalWeight;
+    for (const choice of this.clusterChoices) {
+      if (randomNumber < choice.numerator) {
+        return choice.name;
+      }
+    }
+    // This should be prevented by the validation rules
+    return '';
+  }
+
+  toString() {
+    return 'WeightedCluster(' + this.clusters.map(({name, weight}) => '(' + name + ':' + weight + ')').join(', ') + ')';
+  }
+}
\ No newline at end of file