grpc长连接keepalive

项目中碰到了grpc双向流和单向流出现了服务端流context报错：context cancel error，而客户端无感知连接断开，依然认为还在连接中，导致数据传输中断。

遇到这种情况从以下几个维度去思考问题发生的可能：

• 网络是否稳定，能否复现
• 客户端和服务端是否有对context进行cancel
• 客户端和服务端是否有去处理context的cancel信号

由于出现的问题不是在开发环境中，因此开始只能看日志进行排查，但是日志中只得到了服务端会收到context的cancel信号，而客户端没有任何异常。因此尝试能否在开发环境复现，通过拔掉客户端网线后重现了这个异常。解决的方法也很简单，可以在流式接口中加上心跳，如果多久没有收到心跳就断连重连。但是否有更简洁更优雅的方式呢？有的，答案就是grpc的keepalive参数。

keepalive ping 是一种通过传输发送 HTTP2 ping 来检查通道当前是否正在工作的方法。它是周期性发送的，如果 ping 在一定的超时时间内没有得到对等方的确认，则传输断开。

// ClientParameters is used to set keepalive parameters on the client-side.
// These configure how the client will actively probe to notice when a
// connection is broken and send pings so intermediaries will be aware of the
// liveness of the connection. Make sure these parameters are set in
// coordination with the keepalive policy on the server, as incompatible
// settings can result in closing of connection.
type ClientParameters struct {
	// After a duration of this time if the client doesn't see any activity it
	// pings the server to see if the transport is still alive.
	// If set below 10s, a minimum value of 10s will be used instead.
	Time time.Duration // The current default value is infinity.
	// After having pinged for keepalive check, the client waits for a duration
	// of Timeout and if no activity is seen even after that the connection is
	// closed.
	Timeout time.Duration // The current default value is 20 seconds.
	// If true, client sends keepalive pings even with no active RPCs. If false,
	// when there are no active RPCs, Time and Timeout will be ignored and no
	// keepalive pings will be sent.
	PermitWithoutStream bool // false by default.
}

keepalive.ClientParameters 参数的含义如下:

• Time：如果没有 activity， 则每隔此值发送一个 ping 包
• Timeout： 如果 ping ack 该值之内未返回则认为连接已断开
• PermitWithoutStream：如果没有 active 的 stream， 是否允许发送 ping

// ServerParameters is used to set keepalive and max-age parameters on the
// server-side.
type ServerParameters struct {
	// MaxConnectionIdle is a duration for the amount of time after which an
	// idle connection would be closed by sending a GoAway. Idleness duration is
	// defined since the most recent time the number of outstanding RPCs became
	// zero or the connection establishment.
	MaxConnectionIdle time.Duration // The current default value is infinity.
	// MaxConnectionAge is a duration for the maximum amount of time a
	// connection may exist before it will be closed by sending a GoAway. A
	// random jitter of +/-10% will be added to MaxConnectionAge to spread out
	// connection storms.
	MaxConnectionAge time.Duration // The current default value is infinity.
	// MaxConnectionAgeGrace is an additive period after MaxConnectionAge after
	// which the connection will be forcibly closed.
	MaxConnectionAgeGrace time.Duration // The current default value is infinity.
	// After a duration of this time if the server doesn't see any activity it
	// pings the client to see if the transport is still alive.
	// If set below 1s, a minimum value of 1s will be used instead.
	Time time.Duration // The current default value is 2 hours.
	// After having pinged for keepalive check, the server waits for a duration
	// of Timeout and if no activity is seen even after that the connection is
	// closed.
	Timeout time.Duration // The current default value is 20 seconds.
}

// EnforcementPolicy is used to set keepalive enforcement policy on the
// server-side. Server will close connection with a client that violates this
// policy.
type EnforcementPolicy struct {
	// MinTime is the minimum amount of time a client should wait before sending
	// a keepalive ping.
	MinTime time.Duration // The current default value is 5 minutes.
	// If true, server allows keepalive pings even when there are no active
	// streams(RPCs). If false, and client sends ping when there are no active
	// streams, server will send GOAWAY and close the connection.
	PermitWithoutStream bool // false by default.
}

keepalive.EnforcementPolicy：

• MinTime：如果客户端两次 ping 的间隔小于此值，则关闭连接
• PermitWithoutStream： 即使没有 active stream, 也允许 ping

keepalive.ServerParameters：

• MaxConnectionIdle：如果一个 client 空闲超过该值, 发送一个 GOAWAY, 为了防止同一时间发送大量 GOAWAY, 会在此时间间隔上下浮动 10%, 例如设置为15s，即 15+1.5 或者 15-1.5
• MaxConnectionAge：如果任意连接存活时间超过该值, 发送一个 GOAWAY
• MaxConnectionAgeGrace：在强制关闭连接之间, 允许有该值的时间完成 pending 的 rpc 请求
• Time： 如果一个 client 空闲超过该值, 则发送一个 ping 请求
• Timeout： 如果 ping 请求该时间段内未收到回复, 则认为该连接已断开

https://github.com/grpc/grpc-go/blob/master/examples/features/keepalive/server/main.go

https://github.com/grpc/grpc-go/blob/master/examples/features/keepalive/client/main.go