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Setting up a new node service with TChannel, Thrift & Hyperbahn

This guide will show you how to write a server and client.

The code matching this guide is here.

Table of contents

Dependencies

Make sure you have node and npm installed. To get started create an empty project with npm init and run npm install tchannel --save.

You will also need to run a Hyperbahn ring locally. How to setup hyperbahn is out of scope for this document but hopefully you can find instructions elsewhere.

Defining your service

To define the interface of your service you can create a Thrift file.

Today we will use:

keyvalue.thrift:

struct GetResult {
    1: string value
}

service KeyValue {
    GetResult get_v1(
        1: string key
    )
    void put_v1(
        1: string key,
        2: string value
    )
}

Our service will have two tchannel endpoints that can be accessed. Namely KeyValue::get_v1 and KeyValue::put_v1.

Writing a tchannel server

To get a server up and running you need to do the following:

  1. Create a TChannel and listen on a port
  2. Configure your endpoint handlers using TChannelThrift
  3. Create a hyperbahn client and advertise with hyperbahn

Creating a tchannel

Create a tchannel using TChannel(opts) and listen to it by calling .listen(port, host).

It's advised that you listen on the external IP of your host to ensure that other machines can create incoming connections to you. Consider using my-local-ip to determine your external IP.

When you create your channel make sure you configure the correct options for your use cases. See the tchannel docs for more details.

var TChannel = require('tchannel');
var myLocalIp = require('my-local-ip');

var rootChannel = TChannel();
rootChannel.listen(4040, myLocalIp());

Creating and registering your handlers

To register your interface you must implement the get and put endpoints on your tchannel.

First we create a sub channel using channel.makeSubChannel().

Once we have a sub channel we have to create a TChannelThrift(opts) codec.

Finally you can call .register() on the thrift codec to register your actual endpoints.

var TChannelThrift = rootChannel.TChannelAsThrift;

var keyChan = rootChannel.makeSubChannel({
    serviceName: 'keyvalue'
});
var keyThrift = TChannelThrift({
    entryPoint: path.join(__dirname, 'keyvalue.thrift')
});
var ctx = {
    store: {}
};

keyThrift.register(keyChan, 'KeyValue::get_v1', ctx, get);
keyThrift.register(keyChan, 'KeyValue::put_v1', ctx, put);

function get(context, req, head, body, cb) {
    cb(null, {
        ok: true,
        body: {
            value: context.store[body.key]
        }
    });
}
function put(context, req, head, body, cb) {
    context.store[body.key] = body.value;
    cb(null, {
        ok: true,
        body: null
    });
}

Testing your server with tcurl

You can test your server by making a call using tcurl

To install tcurl, please run npm install tcurl -g

tcurl -p 127.0.0.1:4040 -t [DIR-TO-THRIFT] keyvalue KeyValue::put_v1 -3 '{"key":"hello","value":"world"}'
tcurl -p 127.0.0.1:4040 -t [DIR-TO-THRIFT] keyvalue KeyValue::get_v1 -3 '{"key":"hello"}'

Make sure you that you have a folder containing the thrift definition. The thrift file should be called keyvalue.thrift.

Looking at your service with tcap

You can see what's actually happening by using tcap the tchannel network introspection tool.

To install tcap, please run npm install tcap -g

sudo tcap -p 4040 -i eth0 -i en0 -i lo -s keyvalue
tcurl -p 127.0.0.1:4040 -t [DIR-TO-THRIFT] keyvalue KeyValue::put_v1 -3 '{"key":"hello","value":"world"}'

Setting up hyperbahn

You need to setup hyperbahn locally. See the running hyperbahn locally docs

Registering with hyperbahn

Create a Hyperbahn client using HyperbahnClient(opts).

Call .advertise() on the hyperbahn client to advertise your service with hyperbahn.

var HyperbahnClient = require('tchannel/hyperbahn/');

var hyperbahnClient = HyperbahnClient({
    tchannel: rootChannel,
    serviceName: 'keyvalue',
    hostPortList: ['127.0.0.1:21301'],
    hardFail: true
});

hyperbahnClient.advertise();
hyperbahnClient.once('advertised', onAdvertised);

function onAdvertised() {
    /* hooray! */
}

Testing against hyperbahn

Your service is now available on hyperbahn. You can test this by making a call using tcurl

To install tcurl, please run npm install tcurl -g

tcurl -p [HYPERBAHN-HOSTPORT] -t [DIR-TO-THRIFT] keyvalue KeyValue::put_v1 -3 '{"key":"hello","value":"world"}'
tcurl -p [HYPERBAHN-HOSTPORT] -t [DIR-TO-THRIFT] keyvalue KeyValue::get_v1 -3 '{"key":"hello"}'

Make sure to replace [HYPERBAHN-HOSTPORT] with one of the hyperbahn instance host ports and [DIR-TO-THRIFT] with a folder where the thrift files are stored.

Your service can be accessed over Hyperbahn + TChannel from any language.

You can also see the traffic flowing through hyperbahn using tcap

sudo tcap -p 21301 -i lo

Writing a tchannel client

To make a client that talks to hyperbhan, you need to:

  • Create a tchannel
  • Create a hyperbahn client
  • Making outgoing call requests using TChannelThrift codec

Creating a tchannel

TChannel is a bidirectional RPC library; you already know how to create a root channel.

A pure client does not need to call .listen() but it's recommended that you .listen() anyway and advertise() anyway. It's always best to get onto the hyperbahn as early as possible.

Feel free to re-use the rootChannel that you made for the server

Creating a hyperbahn client

The hyperbahn client is bidirectional. You already know how to create a hyperbahn client.

Technically you do not need to advertise() as a pure client but it's recommended that you do so.

Feel free to re-use the hyperbahnClient that you made for the server

Making outgoing call requests using the tchannelThrift codec

To make an outgoing call request you will need a sub channel for the service you are talking to. Use hyperbahnClient.getClientChannel(opts) to get a sub channel

Once you have a subchannel you can create a thrift codec using TChannelThrift(opts)

Finally we call .request() on the thrift codec.

var hyperbahnClient = HyperbahnClient({
    tchannel: rootChannel,
    serviceName: 'keyvalue-client',
    hostPortList: ['127.0.0.1:21301'],
    hardFail: true
});

var keyChan = hyperbahnClient.getClientChannel({
    serviceName: 'keyvalue'
});
var keyThrift = rootChannel.TChannelAsThrift({
    entryPoint: path.join(__dirname, 'keyvalue.thrift'),
    channel: keyChan
});

keyThrift.request({
    serviceName: 'keyvalue',
    timeout: 100
}).send('KeyValue::put_v1', null, {
    key: 'hello',
    value: 'world'
}, function onResponse(err, resp) {
    if (err) {
        return logger.error('got an error', {
            error: err
        });
    }

    logger.info('got result', {
        ok: resp.ok,
        body: resp.body
    });
});

Getting started with a real service

Now that you've followed the guide it's recommended that you use the scaffolder for getting a real service up and running.

You can https://github.com/Raynos/tchannel-gen to scaffold out a new service and this will include all of the bootstrapping, ringpop and testing infrastructure as well as example tests.