Traffic Router

Introduction

Traffic Router is a Java Tomcat application that routes clients to the closest available cache on the CDN using both HTTP and DNS. Cache availability is determined by Traffic Monitor; consequently Traffic Router polls Traffic Monitor for its configuration and cache health state information, and uses this data to make routing decisions. HTTP routing is performed by localizing the client based on the request’s source IP address (IPv4 or IPv6), and issues an HTTP 302 redirect to the nearest cache. HTTP routing utilizes consistent hashing on request URLs to optimize cache performance and request distribution. DNS routing is performed by localizing clients, resolvers in most cases, requesting A and AAAA records for a configurable name such as edge.deliveryservice.somecdn.net. Traffic Router is comprised of four separate Maven modules:

  • api - Provides a simple JSON interface into certain aspects of core and is deployed as a WAR to a Service (read: connector/listen port) within Tomcat which is separate from core
  • connector - A JAR that overrides Tomcat’s standard Http11Protocol Connector class and allows Traffic Router to delay opening listen sockets until it is in a state suitable for routing traffic
  • geolocation - Submodule for defining geolocation services
  • testServer - A convenience server for easier manual testing of the API portion of Traffic Router on a development machine
  • core - Services DNS and HTTP requests, performs localization on routing requests, and is deployed as a WAR to a Service (read: connector/listen port) within Tomcat which is separate from api
  • rpm - A simple Maven project which gathers the artifacts from the prior three modules and builds an RPM

Software Requirements

To work on Traffic Router you need a *nix (MacOS and Linux are most commonly used) environment that has the following installed:

  • Eclipse >= Kepler SR2 (or another Java IDE)
  • Maven >= 3.3.1
  • JDK >= 6.0

Traffic Router Project Tree Overview

  • traffic_control/traffic_traffic_router/ - base directory for Traffic Router

    • api/ - Source code for Traffic Router API, which is built as its own deployable WAR file and communicates with Traffic Router Core using JMX

      • src/main - Main source directory for Traffic Router API

        • java/ - Java source code for Traffic Router API
        • resources/ - Spring resources pulled in during an RPM build
        • webapp/ - Java webapp resources
      • src/test - Test source directory for Traffic Router API

        • java/ - JUnit based unit tests for Traffic Router API
        • resources/ - Resources pulled in by unit tests
    • connector/ - Source code for Traffic Router Connector;

      • src/main/java - Java source directory for Traffic Router Connector
    • core/ - Source code for Traffic Router Core, which is built as its own deployable WAR file and communicates with Traffic Router API using JMX

      • src/main - Main source directory for Traffic Router Core

        • etc/init.d - Init script for Tomcat
        • conf/ - Minimum required configuration files
        • java/ - Java source code for Traffic Router Core
        • opt/tomcat/conf - Contains Tomcat configuration file(s) pulled in during an RPM build
        • resources/ - Resources pulled in during an RPM build
        • scripts/ - Scripts used by the RPM build process
        • webapp/ - Java webapp resources
      • src/test - Test source directory for Traffic Router Core

        • conf/ - Minimal Configuration files that make it possible to run junit tests

        • db/ - Files downloaded by unit tests

        • java/ - JUnit based unit tests for Traffic Router Core

        • resources/ - Example data files used by junit tests

          • var/auto-zones - BIND formatted zone files generated by Traffic Router Core during unit testing

Java Formatting Conventions

None at this time. The codebase will eventually be formatted per Java standards.

Installing The Developer Environment

To install the Traffic Router Developer environment:

  1. Clone the traffic_control repository using Git.

  2. Change directories into traffic_control/traffic_router.

  3. Follow the instructions in “README.DNSSEC” for DNSSEC support.

  4. Set the environment variable TRAFFIC_MONITOR_HOSTS to be a semicolon delimited list of Traffic Monitors that can be accessed during integration tests

  5. Additional configuration is set using the below files:
    • core/src/test/resources no longer exists

    • core/src/test/conf/traffic_ops.properties file holds the credentials for accessing Traffic Ops.

    • Default configuration values now reside in core/src/main/webapp/WEB-INF/applicationContext.xml

    • The above values may be overridden by creating and/or modifying the property files listed in core/src/main/resources/applicationProperties.xml

    • Pre-existing properties files are still honored by Traffic Router. For example traffic_monitor.properties:

      Parameter Value
      traffic_monitor.bootstrap.hosts FQDN and port of the Traffic Monitor instance(s), separated by semicolons as necessary (do not include http://).
  6. Import the existing git repo into Eclipse:

    1. File -> Import -> Git -> Projects from Git; Next
    2. Existing local repository; Next
    3. Add -> browse to find traffic_control; Open
    4. Select traffic_control; Next
    5. Ensure “Import existing projects” is selected, expand traffic_control, select traffic_router; Next
    6. Ensure traffic_router_api, traffic_router_connector, and traffic_router_core are checked; Finish (this step can take several minutes to complete)
    7. Ensure traffic_router_api, traffic_router_connector, and traffic_router_core have been opened by Eclipse after importing
  7. From the terminal, run mvn clean verify from the traffic_router directory

  8. Start the embedded Jetty instance for Core from within Eclipse

    1. In the package explorer, expand traffic_router_core

    2. Expand src/test/java

    3. Expand the package com.comcast.cdn.traffic_control.traffic_router.core

    4. Open and run TrafficRouterStart.java

      Note

      If an error is displayed in the Console, run mvn clean verify from the traffic_router directory

  9. Traffic Router Core should now be running; the HTTP routing interface is available on http://localhost:8081, while HTTPS is available on http://localhost:8443. The DNS server and routing interface is available on localhost:1053 via TCP and UDP.

Test Cases

  • Unit tests can be executed using Maven by running mvn test at the root of the traffic_router project.
  • Unit and Integration tests can be executed using Maven by running mvn verify at the root of the traffic_router project.

RPM Packaging

Running mvn package on a Linux based distribution will trigger the build process to create the Traffic Router rpm.