diff --git a/packages/grpc-js/src/load-balancing-config.ts b/packages/grpc-js/src/load-balancing-config.ts
new file mode 100644
index 00000000..b4b4594d
--- /dev/null
+++ b/packages/grpc-js/src/load-balancing-config.ts
@@ -0,0 +1,109 @@
+/*
+ * Copyright 2019 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.
+ *
+ */
+
+/* This file is an implementation of gRFC A24:
+ * https://github.com/grpc/proposal/blob/master/A24-lb-policy-config.md */
+
+import { isString, isArray } from "util";
+
+export interface RoundRobinConfig {
+}
+
+export interface XdsConfig {
+  balancerName: string;
+  childPolicy: LoadBalancingConfig[];
+  fallbackPolicy: LoadBalancingConfig[];
+}
+
+export interface GrpcLbConfig {
+  childPolicy: LoadBalancingConfig[];
+}
+
+export interface LoadBalancingConfig {
+  /* Exactly one of these must be set for a config to be valid */
+  round_robin?: RoundRobinConfig;
+  xds?: XdsConfig;
+  grpclb?: GrpcLbConfig;
+}
+
+/* In these functions we assume the input came from a JSON object. Therefore we
+ * expect that the prototype is uninteresting and that `in` can be used
+ * effectively */
+
+function validateXdsConfig(xds: any): XdsConfig {
+  if (!('balancerName' in xds) || !isString(xds.balancerName)) {
+    throw new Error('Invalid xds config: invalid balancerName');
+  }
+  const xdsConfig: XdsConfig = {
+    balancerName: xds.balancerName,
+    childPolicy: [],
+    fallbackPolicy: []
+  };
+  if ('childPolicy' in xds) {
+    if (!isArray(xds.childPolicy)) {
+      throw new Error('Invalid xds config: invalid childPolicy');
+    }
+    for (const policy of xds.childPolicy) {
+      xdsConfig.childPolicy.push(validateConfig(policy));
+    }
+  }
+  if ('fallbackPolicy' in xds) {
+    if (!isArray(xds.fallbackPolicy)) {
+      throw new Error('Invalid xds config: invalid fallbackPolicy');
+    }
+    for (const policy of xds.fallbackPolicy) {
+      xdsConfig.fallbackPolicy.push(validateConfig(policy));
+    }
+  }
+  return xdsConfig;
+}
+
+function validateGrpcLbConfig(grpclb: any): GrpcLbConfig {
+  const grpcLbConfig: GrpcLbConfig = {
+    childPolicy: []
+  };
+  if ('childPolicy' in grpclb) {
+    if (!isArray(grpclb.childPolicy)) {
+      throw new Error('Invalid xds config: invalid childPolicy');
+    }
+    for (const policy of grpclb.childPolicy) {
+      grpcLbConfig.childPolicy.push(validateConfig(policy));
+    }
+  }
+  return grpcLbConfig;
+}
+
+export function validateConfig(obj: any): LoadBalancingConfig {
+  if ('round_robin' in obj) {
+    if ('xds' in obj || 'grpclb' in obj) {
+      throw new Error('Multiple load balancing policies configured');
+    }
+    if (obj['round_robin'] instanceof Object) {
+      return { round_robin: {} }
+    }
+  }
+  if ('xds' in obj) {
+    if ('grpclb' in obj) {
+      throw new Error('Multiple load balancing policies configured');
+    }
+    return {xds: validateXdsConfig(obj.xds)};
+  }
+  if ('grpclb' in obj) {
+    return {grpclb: validateGrpcLbConfig(obj.grpclb)};
+  }
+  throw new Error('No recognized load balancing policy configured');
+}
\ No newline at end of file
diff --git a/packages/grpc-js/src/resolver-dns.ts b/packages/grpc-js/src/resolver-dns.ts
new file mode 100644
index 00000000..d556aebc
--- /dev/null
+++ b/packages/grpc-js/src/resolver-dns.ts
@@ -0,0 +1,144 @@
+/*
+ * Copyright 2019 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 { Resolver, ResolverListener, registerResolver, registerDefaultResolver } from './resolver';
+import * as dns from 'dns';
+import * as util from 'util';
+import { extractAndSelectServiceConfig, ServiceConfig } from './service-config';
+
+/* These regular expressions match IP addresses with optional ports in different
+ * formats. In each case, capture group 1 contains the address, and capture
+ * group 2 contains the port number, if present */
+const IPv4_REGEX = /^(\d{1,3}(?:\.\d{1,3}){3})(?::(\d+))?$/;
+const IPv6_REGEX = /^([0-9a-f]{0,4}(?::{1,2}[0-9a-f]{0,4})+)$/i;
+const IPv6_BRACKET_REGEX = /^\[([0-9a-f]{0,4}(?::{1,2}[0-9a-f]{0,4})+)\](?::(\d+))?$/i;
+
+const DNS_REGEX = /^(?:dns:)?(?:\/\/\w+\/)?(\w+)(?::(\d+))?$/;
+
+const DEFAULT_PORT = '443';
+
+const resolve4Promise = util.promisify(dns.resolve4);
+const resolve6Promise = util.promisify(dns.resolve6);
+
+function parseIP(target: string): string | null {
+  /* These three regular expressions are all mutually exclusive, so we just
+   * want the first one that matches the target string, if any do. */
+  const match = IPv4_REGEX.exec(target) || IPv6_REGEX.exec(target) || IPv6_BRACKET_REGEX.exec(target);
+  if (match === null) {
+    return null;
+  }
+  const addr = match[1];
+  let port: string;
+  if (match[2]) {
+    port = match[2];
+  } else {
+    port = DEFAULT_PORT;
+  }
+  return `${addr}:${port}`;
+}
+
+function mergeArrays<T>(...arrays: T[][]): T[] {
+  const result: T[] = [];
+  for(let i = 0; i<Math.max.apply(null, arrays.map((array)=> array.length)); i++) {
+    for(let array of arrays) {
+      if(i < array.length) {
+        result.push(array[i]);
+      }
+    }
+  }
+  return result;
+}
+
+class DnsResolver implements Resolver {
+  ipResult: string | null;
+  dnsHostname: string | null;
+  port: string | null;
+  /* The promise results here contain, in order, the A record, the AAAA record,
+   * and either the TXT record or an error if TXT resolution failed */
+  pendingResultPromise: Promise<[string[], string[], string[][] | Error]> | null = null;
+  percentage: number;
+  constructor(private target: string, private listener: ResolverListener) {
+    this.ipResult = parseIP(target);
+    const dnsMatch = DNS_REGEX.exec(target);
+    if (dnsMatch === null) {
+      this.dnsHostname = null;
+      this.port = null;
+    } else {
+      this.dnsHostname = dnsMatch[1];
+      if (dnsMatch[2]) {
+        this.port = dnsMatch[2];
+      } else {
+        this.port = DEFAULT_PORT;
+      }
+    }
+    this.percentage = Math.random() * 100;
+    this.startResolution();
+  }
+
+  private startResolution() {
+    if (this.ipResult !== null) {
+      setImmediate(() => {
+        this.listener.onSuccessfulResolution([this.ipResult!], null, null);
+      });
+      return;
+    }
+    if (this.dnsHostname !== null) {
+      const hostname: string = this.dnsHostname;
+      const Aresult = resolve4Promise(hostname);
+      const AAAAresult = resolve6Promise(hostname);
+      const TXTresult = new Promise<string[][] | Error>((resolve, reject) => {
+        dns.resolveTxt(hostname, (err, records) => {
+          if (err) {
+            resolve(err);
+          } else {
+            resolve(records);
+          }
+        });
+      });
+      this.pendingResultPromise = Promise.all([Aresult, AAAAresult, TXTresult]);
+      this.pendingResultPromise.then(([Arecord, AAAArecord, TXTrecord]) => {
+        this.pendingResultPromise = null;
+        const allAddresses: string[] = mergeArrays(AAAArecord, Arecord);
+        let serviceConfig: ServiceConfig | null = null;
+        let serviceConfigError: Error | null = null;
+        if (TXTrecord instanceof Error) {
+          serviceConfigError = TXTrecord;
+        } else {
+          try {
+            serviceConfig = extractAndSelectServiceConfig(TXTrecord, this.percentage);
+          } catch (err) {
+            serviceConfigError = err;
+          }
+        }
+        this.listener.onSuccessfulResolution(allAddresses, serviceConfig, serviceConfigError);
+      }, (err) => {
+        this.pendingResultPromise = null;
+        this.listener.onError(err);
+      });
+    }
+  }
+
+  updateResolution() {
+    if (this.pendingResultPromise === null) {
+      this.startResolution();
+    }
+  }
+}
+
+export function setup(): void {
+  registerResolver('dns:', DnsResolver);
+  registerDefaultResolver(DnsResolver);
+}
\ No newline at end of file
diff --git a/packages/grpc-js/src/resolver.ts b/packages/grpc-js/src/resolver.ts
new file mode 100644
index 00000000..e5519a9b
--- /dev/null
+++ b/packages/grpc-js/src/resolver.ts
@@ -0,0 +1,55 @@
+/*
+ * Copyright 2019 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 { ServiceError } from "./call";
+import { ServiceConfig } from "./service-config";
+
+export interface ResolverListener {
+  onSuccessfulResolution(addressList: string[], serviceConfig: ServiceConfig | null, serviceConfigError: Error | null): void;
+  onError(error: ServiceError): void;
+}
+
+export interface Resolver {
+  updateResolution(): void;
+}
+
+export interface ResolverConstructor {
+  new(target: string, listener: ResolverListener): Resolver;
+}
+
+const registeredResolvers: {[prefix: string]: ResolverConstructor} = {};
+let defaultResolver: ResolverConstructor | null = null;
+
+export function registerResolver(prefix: string, resolverClass: ResolverConstructor) {
+  registeredResolvers[prefix] = resolverClass;
+}
+
+export function registerDefaultResolver(resolverClass: ResolverConstructor) {
+  defaultResolver = resolverClass;
+}
+
+export function createResolver(target: string, listener: ResolverListener): Resolver {
+  for (const prefix of Object.keys(registeredResolvers)) {
+    if (target.startsWith(prefix)) {
+      return new registeredResolvers[prefix](target, listener);
+    }
+  }
+  if (defaultResolver !== null) {
+    return new defaultResolver(target, listener);
+  }
+  throw new Error('No resolver could be created for the provided target');
+}
\ No newline at end of file
diff --git a/packages/grpc-js/src/service-config.ts b/packages/grpc-js/src/service-config.ts
new file mode 100644
index 00000000..c181f87b
--- /dev/null
+++ b/packages/grpc-js/src/service-config.ts
@@ -0,0 +1,259 @@
+/*
+ * Copyright 2019 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.
+ *
+ */
+
+/* This file implements gRFC A2 and the service config spec:
+ * https://github.com/grpc/proposal/blob/master/A2-service-configs-in-dns.md
+ * https://github.com/grpc/grpc/blob/master/doc/service_config.md */
+
+import * as lbconfig from './load-balancing-config';
+import { isString, isArray, isBoolean, isNumber } from 'util';
+import * as os from 'os';
+
+export interface MethodConfigName {
+  service: string;
+  method?: string;
+}
+
+export interface MethodConfig {
+  name: MethodConfigName[];
+  waitForReady?: boolean;
+  timeout?: string;
+  maxRequestBytes?: number;
+  maxResponseBytes?: number;
+}
+
+export interface ServiceConfig {
+  loadBalancingPolicy?: string;
+  loadBalancingConfig: lbconfig.LoadBalancingConfig[]
+  methodConfig: MethodConfig[];
+}
+
+export interface ServiceConfigCanaryConfig {
+  clientLanguage?: string[];
+  percentage?: number;
+  clientHostname?: string[];
+  serviceConfig: ServiceConfig;
+}
+
+const TIMEOUT_REGEX = /^\d+(\.\d{1,9})?s$/;
+
+const CLIENT_LANGUAGE_STRING = 'node';
+
+function validateName(obj: any): MethodConfigName {
+  if (!('service' in obj) || !isString(obj.service)) {
+    throw new Error('Invalid method config name: invalid service');
+  }
+  const result: MethodConfigName = {
+    service: obj.service
+  };
+  if ('method' in obj) {
+    if (isString(obj.method)) {
+      result.method = obj.method;
+    } else {
+      throw new Error('Invalid method config name: invalid method');
+    }
+  }
+  return result;
+}
+
+function validateMethodConfig(obj: any): MethodConfig {
+  const result: MethodConfig = {
+    name: []
+  };
+  if (!('name' in obj) || !isArray(obj.name)) {
+    throw new Error('Invalid method config: invalid name array');
+  }
+  for (const name of obj.name) {
+    result.name.push(validateName(name));
+  }
+  if ('waitForReady' in obj) {
+    if (!isBoolean(obj.waitForReady)) {
+      throw new Error('Invalid method config: invalid waitForReady');
+    }
+    result.waitForReady = obj.waitForReady;
+  }
+  if ('timeout' in obj) {
+    if (!isString(obj.timeout) || !TIMEOUT_REGEX.test(obj.timeout)) {
+      throw new Error('Invalid method config: invalid timeout');
+    }
+    result.timeout = obj.timeout;
+  }
+  if ('maxRequestBytes' in obj) {
+    if (!isNumber(obj.maxRequestBytes)) {
+      throw new Error('Invalid method config: invalid maxRequestBytes');
+    }
+    result.maxRequestBytes = obj.maxRequestBytes;
+  }
+  if ('maxResponseBytes' in obj) {
+    if (!isNumber(obj.maxResponseBytes)) {
+      throw new Error('Invalid method config: invalid maxRequestBytes');
+    }
+    result.maxResponseBytes = obj.maxResponseBytes;
+  }
+  return result;
+}
+
+function validateServiceConfig(obj: any): ServiceConfig {
+  const result: ServiceConfig = {
+    loadBalancingConfig: [],
+    methodConfig: []
+  };
+  if ('loadBalancingPolicy' in obj) {
+    if (isString(obj.loadBalancingPolicy)) {
+      result.loadBalancingPolicy = obj.loadBalancingPolicy;
+    } else {
+      throw new Error('Invalid service config: invalid loadBalancingPolicy');
+    }
+  }
+  if ('loadBalancingConfig' in obj) {
+    if (isArray(obj.loadBalancingConfig)) {
+      for (const config of obj.loadBalancingConfig) {
+        result.loadBalancingConfig.push(lbconfig.validateConfig(config));
+      }
+    } else {
+      throw new Error('Invalid service config: invalid loadBalancingConfig');
+    }
+  }
+  if ('methodConfig' in obj) {
+    if (isArray(obj.methodConfig)) {
+      for (const methodConfig of obj.methodConfig) {
+        result.methodConfig.push(validateMethodConfig(methodConfig));
+      }
+    }
+  }
+  // Validate method name uniqueness
+  const seenMethodNames: MethodConfigName[] = [];
+  for (const methodConfig of result.methodConfig) {
+    for (const name of methodConfig.name) {
+      for (const seenName of seenMethodNames) {
+        if (name.service === seenName.service && name.method === seenName.method) {
+          throw new Error(`Invalid service config: duplicate name ${name.service}/${name.method}`);
+        }
+      }
+      seenMethodNames.push(name);
+    }
+  }
+  return result;
+}
+
+function validateCanaryConfig(obj: any): ServiceConfigCanaryConfig {
+  if (!('serviceConfig' in obj)) {
+    throw new Error('Invalid service config choice: missing service config');
+  }
+  const result: ServiceConfigCanaryConfig = {
+    serviceConfig: validateServiceConfig(obj.serviceConfig)
+  }
+  if ('clientLanguage' in obj) {
+    if (isArray(obj.clientLanguage)) {
+      result.clientLanguage = [];
+      for (const lang of obj.clientLanguage) {
+        if (isString(lang)) {
+          result.clientLanguage.push(lang);
+        } else {
+          throw new Error('Invalid service config choice: invalid clientLanguage');
+        }
+      }
+    } else {
+      throw new Error('Invalid service config choice: invalid clientLanguage');
+    }
+  }
+  if ('clientHostname' in obj) {
+    if (isArray(obj.clientHostname)) {
+      result.clientHostname = [];
+      for (const lang of obj.clientHostname) {
+        if (isString(lang)) {
+          result.clientHostname.push(lang);
+        } else {
+          throw new Error('Invalid service config choice: invalid clientHostname');
+        }
+      }
+    } else {
+      throw new Error('Invalid service config choice: invalid clientHostname');
+    }
+  }
+  if ('percentage' in obj) {
+    if (isNumber(obj.percentage) && 0 <= obj.percentage && obj.percentage <= 100) {
+      result.percentage = obj.percentage;
+    } else {
+      throw new Error('Invalid service config choice: invalid percentage');
+    }
+  }
+  // Validate that no unexpected fields are present
+  const allowedFields = ['clientLanguage', 'percentage', 'clientHostname', 'serviceConfig'];
+  for (const field in obj) {
+    if (!allowedFields.includes(field)) {
+      throw new Error(`Invalid service config choice: unexpected field ${field}`);
+    }
+  }
+  return result;
+}
+
+function validateAndSelectCanaryConfig(obj: any, percentage: number): ServiceConfig {
+  if (!isArray(obj)) {
+    throw new Error('Invalid service config list');
+  }
+  for (const config of obj) {
+    const validatedConfig = validateCanaryConfig(config);
+    /* For each field, we check if it is present, then only discard the
+     * config if the field value does not match the current client */
+    if (isNumber(validatedConfig.percentage) && percentage > validatedConfig.percentage) {
+      continue;
+    }
+    if (isArray(validatedConfig.clientHostname)) {
+      let hostnameMatched = false;
+      for (const hostname of validatedConfig.clientHostname) {
+        if (hostname === os.hostname()) {
+          hostnameMatched = true;
+        }
+      }
+      if (!hostnameMatched) {
+        continue;
+      }
+    }
+    if (isArray(validatedConfig.clientLanguage)) {
+      let languageMatched = false;
+      for (const language of validatedConfig.clientLanguage) {
+        if (language === CLIENT_LANGUAGE_STRING) {
+          languageMatched = true;
+        }
+      }
+      if (!languageMatched) {
+        continue;
+      }
+    }
+    return validatedConfig.serviceConfig;
+  }
+  throw new Error('No matching service config found');
+}
+
+/**
+ * Find the "grpc_config" record among the TXT records, parse its value as JSON, validate its contents,
+ * and select a service config with selection fields that all match this client. Most of these steps
+ * can fail with an error; the caller must handle any errors thrown this way.
+ * @param txtRecord The TXT record array that is output from a successful call to dns.resolveTxt
+ * @param percentage A number chosen from the range [0, 100) that is used to select which config to use
+ */
+export function extractAndSelectServiceConfig(txtRecord: string[][], percentage: number): ServiceConfig | null {
+  for (const record of txtRecord) {
+    if (record.length > 0 && record[0].startsWith('grpc_config=')) {
+      const recordString = [record[0].substring('grpc_config='.length)].concat(record.slice(1)).join('');
+      const recordJson: any = JSON.parse(recordString);
+      return validateAndSelectCanaryConfig(recordJson, percentage);
+    }
+  }
+  return null;
+}
\ No newline at end of file