ION的基本架构 | Yin的笔记本

服务名称	功能
ISLB	节点发现与负载均衡
Signal	传递信令
Room	主要业务逻辑，包括聊天室、用户验证等
SFU	WebRTC SFU，用于视频流的转发

用到的独立软件	功能
Redis	缓存数据库。给ISLB存储节点列表等数据；给Room存储业务逻辑数据
nats	分布式消息队列。用于各服务间的消息传递

Software applications and services need to exchange data. NATS is an infrastructure that allows such data exchange, segmented in the form of messages. We call this a "message oriented middleware".

在连接建立过程中，各组件之间的关系如下：

SDK<---grpc--->signal<---nats--->Room/ISLB<---nats--->signal<---grpc--->SDK
                                    ||
                                  [Redis]

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在视频流传输中，各组件之间的关系如下：

SDK<----webrtc---->SFU<----webrtc---->SDK

# 启动

# SFU

在官网教程中，单独启动SFU的指令如下：

docker pull nats
docker run -p 4222:4222 -p 6222:6222 -p 8222:8222 nats
docker run -p 5000:5000/udp --network host -v $PWD/configs/sfu.toml:/configs/sfu.toml pionwebrtc/ion:latest-sfu

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可以看出，SFU需要有nats的存在才可运行。

$PWD/configs/sfu.toml似乎是配置文件。找到pion/ion-sfu中配置文件的位置，可以看到这文件长这样：

[sfu]
# Ballast size in MiB, will allocate memory to reduce the GC trigger upto 2x the
# size of ballast. Be aware that the ballast should be less than the half of memory
# available.
ballast = 0
# enable prometheus sfu statistics
withstats = false

[router]
# Limit the remb bandwidth in kbps
# zero means no limits
maxbandwidth = 1500
# max number of video tracks packets the SFU will keep track
maxpackettrack = 500
# Sets the audio level volume threshold.
# Values from [0-127] where 0 is the loudest.
# Audio levels are read from rtp extension header according to:
# https://tools.ietf.org/html/rfc6464
audiolevelthreshold = 40
# Sets the interval in which the SFU will check the audio level
# in [ms]. If the active speaker has changed, the sfu will
# emit an event to clients.
audiolevelinterval=1000
# Sets minimum percentage of events required to fire an audio level
# according to the expected events from the audiolevelinterval,
# calculated as audiolevelinterval/packetization time (20ms for 8kHz)
# Values from [0-100]
audiolevelfilter = 20

[router.simulcast]
# Prefer best quality initially
bestqualityfirst = true
# EXPERIMENTAL enable temporal layer change is currently an experimental feature,
# enable only for testing.
enabletemporallayer = false

[webrtc]
# Single port, portrange will not work if you enable this
# singleport = 5000

# Range of ports that ion accepts WebRTC traffic on
# Format: [min, max]   and max - min >= 100
portrange = [5000, 5200]
# if sfu behind nat, set iceserver
# [[webrtc.iceserver]]
# urls = ["stun:stun.stunprotocol.org:3478"]
# [[webrtc.iceserver]]
# urls = ["turn:turn.awsome.org:3478"]
# username = "awsome"
# credential = "awsome"

# sdp semantics:
# "unified-plan"
# "plan-b"
# "unified-plan-with-fallback"
sdpsemantics = "unified-plan"
# toggle multicast dns support: https://tools.ietf.org/html/draft-mdns-ice-candidates-00
mdns = true

[webrtc.candidates]
# In case you're deploying ion-sfu on a server which is configured with
# a 1:1 NAT (e.g., Amazon EC2), you might want to also specify the public
# address of the machine using the setting below. This will result in
# all host candidates (which normally have a private IP address) to
# be rewritten with the public address provided in the settings. As
# such, use the option with caution and only if you know what you're doing.
# Multiple public IP addresses can be specified as a comma separated list
# if the sfu is deployed in a DMZ between two 1-1 NAT for internal and
# external users.
# nat1to1 = ["1.2.3.4"]
# icelite = true

[webrtc.timeouts]
# The duration in [sec] without network activity before a ICE Agent is considered disconnected
disconnected = 5
# The duration in [sec] without network activity before a ICE Agent is considered failed after disconnected
failed = 25
# How often in [sec] the ICE Agent sends extra traffic if there is no activity, if media is flowing no traffic will be sent
keepalive = 2

[turn]
# Enables embeded turn server
enabled = false
# Sets the realm for turn server
realm = "ion"
# The address the TURN server will listen on.
address = "0.0.0.0:3478"
# Certs path to config tls/dtls
# cert="path/to/cert.pem"
# key="path/to/key.pem"
# Port range that turn relays to SFU
# WARNING: It shouldn't overlap webrtc.portrange
# Format: [min, max]
# portrange = [5201, 5400]
[turn.auth]
# Use an auth secret to generate long-term credentials defined in RFC5389-10.2
# NOTE: This takes precedence over `credentials` if defined.
# secret = "secret"
# Sets the credentials pairs
credentials = "pion=ion,pion2=ion2"

[log]
# 0 - INFO 1 - DEBUG 2 - TRACE
v = 1

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可以看到设置还是比较丰富的，比如有maxbandwidth这种带宽设置、WebRTC监听端口范围设置portrange、给内网端口映射环境部署时用的nat1to1、内置turn服务器设置[turn]等。

但是并没看到有nats相关的配置？这个SFU是怎么知道如何连接nats的？在仔细找找，发现这个pion/ion-sfu并不是直接放进容器里，而是在github.com/pion/ion/pkg/node/sfu里面做了一层封装，然后在cmd/sfu/main.go里面调用成为一个可执行文件的。

进一步，进到pkg/node/sfu/sfu.go中，找到最主要的配置项：

// Config for sfu node
type Config struct {
	Global global   `mapstructure:"global"`
	Log    logConf  `mapstructure:"log"`
	Nats   natsConf `mapstructure:"nats"`
	isfu.Config
}

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可以看到，SFU中的配置项实际上是几个配置项拼起来的，其中就包含pion/ion-sfu中配置项isfu.Config。

再找到从这个配置项生成的pion/ion中关于SFU的配置文件：

[global]
# data center id
dc = "dc1"

[nats]
url = "nats://127.0.0.1:4222"


[sfu]
# ......以下配置和上面那个配置文件差不多，省略

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可以看到这就是pion/ion-sfu中配置文件加了几个配置项而已。其中就有nats的配置项，比如地址和数据库名称啥的。

具体原理的解析，且看《ION中的SFU服务》。

# islb

在官网教程中，单独启动islb的指令如下：

docker pull nats
docker run -p 4222:4222 -p 6222:6222 -p 8222:8222 nats
docker pull redis
docker run -p 6379:6379 redis
docker run --network host -v $PWD/configs/islb.toml:/configs/islb.toml pionwebrtc/ion:latest-islb

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可以看出，islb不仅需要有nats，还需要有Redis的存在才可运行。毕竟是负载均衡，肯定要存一下有哪些个节点可供负载均衡。

$PWD/configs/islb.toml应该就是配置文件。和上面一样，直接找到对应的配置文件：

[global]
# data center id
dc = "dc1"

[log]
level = "info"

[nats]
url = "nats://127.0.0.1:4222"


[redis]
addrs = [":6379"]
password = ""
db = 0

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未免也过于简单了，完全就只有连数据库的配置，没有一点自己的运行逻辑方面配置？

从代码结构上看，在pion项目中，这个islb没有单独的包，主要的逻辑都在github.com/pion/ion/pkg/node/islb这个包里面，然后在cmd/islb/main.go里面做成可执行文件。找代码里的配置项也很好找得到：

// Config for islb node
type Config struct {
	Global  global    `mapstructure:"global"`
	Log     logConf   `mapstructure:"log"`
	Nats    natsConf  `mapstructure:"nats"`
	Redis   db.Config `mapstructure:"redis"`
	CfgFile string
}

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这里面确实没有islb相关的配置项。这就怪了，这islb是什么运行逻辑，怎么都没配置的？好歹还是个“负载均衡”来着。

这个问题比较复杂，详见《ION中的islb服务》。总的来说，islb实际上就是一个服务注册中心，并没有所谓的负载均衡功能，存储和查询流信息的功能不知道被移到哪去了。推测这个模块后面应该会改个名字，比如改成“Registry”啥的，更符合它现在的功能。

# Signal

从《ION中的SFU服务》中我们可以看出，信令服务都在SFU里面写好了，那这个Signal是干嘛用的？

先看启动过程。在官网教程中，单独启动Signal的指令如下：

docker pull nats
docker run -p 4222:4222 -p 6222:6222 -p 8222:8222 nats
docker run -p 5551:5551/tcp --network host -v $PWD/configs/signal.toml:/configs/signal.toml pionwebrtc/ion:latest-signal

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可以看出，Signal的启动只需要有nats就行了

这个配置文件是这样：

[global]
# data center id
dc = "dc1"

[log]
level = "info"
# level = "debug"

[nats]
url = "nats://127.0.0.1:4222"


[signal.grpc]
#listen ip port
host = "0.0.0.0"
port = "5551"
allow_all_origins = true
# cert= "configs/certs/cert.pem"
# key= "configs/certs/key.pem"

[signal.jwt]
enabled = false 
key_type = "HMAC"
key = "1q2dGu5pzikcrECJgW3ADfXX3EsmoD99SYvSVCpDsJrAqxou5tUNbHPvkEFI4bTS"

[signal.svc]
services = ["rtc", "room"]

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前面都没啥特殊的。

这个signal.grpc应该是指明Signal服务的对外接口；signal.jwt应该是验证功能；signal.svc这是什么，看着像是什么服务名，不知道有什么用？

打开Signal的主函数看一眼，服务注册之类的代码都和前面介绍的一样，最重要的代码应该就是这段：

	srv := grpc.NewServer(
		grpc.CustomCodec(nrpc.Codec()), // nolint:staticcheck
		grpc.UnknownServiceHandler(nproxy.TransparentLongConnectionHandler(sig.Director)))

	s := util.NewWrapperedGRPCWebServer(util.NewWrapperedServerOptions(
		addr, conf.Signal.GRPC.Cert, conf.Signal.GRPC.Key, true), srv)

	if err := s.Serve(); err != nil {
		log.Panicf("failed to serve: %v", err)
	}
	select {}

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滴滴🤯！！捕捉到关键词proxy！看这样子Signal应该是个GRPC代理，把外面来的标准GRPC请求转换为nats-grpc的请求。

进一步解析详见《ION中的Signal服务》。