关于grpc 的keepalive 的一些知识

1. GRPC keepalive 的相关知识

参照这个连接

// 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.
}// 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.
}

grpc client 的keepalive 用来检测 client 创建的grpc channel 连接是不是可用的，如果超时，就会关掉这个channel 的连接
grpc server 的keepalive 用来检测 server 创建的grpc channel 连接是不是可用的，如果超时，就会关掉这个channel 的连接

在这里还需要特别注意一个问题， grpc client 的keepalive 的时间设定需要在server 允许范围内，否则，server 会认为你是捣蛋的，给你发送一个GOAWAY 消息，把和client 的连接强制关掉
这部分，具体我们来看grpc-go的相关定义：

// 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.
}

够清晰吧，所以在grpc server 端需要设置这个参数，来和client 端作匹配！

如果两者不匹配就会出现下面的错误

closing transport due to: connection error: desc = “error reading from server: EOF”, received prior goaway: code: ENHANCE_YOUR_CALM, debug data: “too_many_pings”

意思就是server 端说：”兄弟，你ping 的手速太快了，哥撑不住了，不带你玩了，滚吧！“。说完就把连接诶给断了。

2. Java grpc server 的一些注意事项

如果要用java 写一个grpc server，此时假定需要设定上面所述的匹配，应该要怎么做?
刚开始我们用的和官方demo一样的方式(io.grpc.ServerBuilder)创建server，但发现这个类io.grpc.ServerBuilder压根没有设置这个keepalive 参数的接口，后来在github 上看到这个issue：
https://github.com/grpc/grpc-java/issues/8991

NettyServerBuilder has the appropriate API. You’d need to use the APIs io.grpc.netty.NettyServerBuilder (and swap to grpc-netty) or the questionable io.grpc.netty.shaded.io.grpc.netty.NettyServerBuilder (to continue with grpc-netty). Neither option is great as grpc-netty-shaded is much preferred over grpc-netty but nominally it doesn’t really expose a public API.
As a short-term “get it working.” Using io.grpc.netty.shaded.io.grpc.netty.NettyServerBuilder is probably fair. But we need to add the keepalive methods to io.grpc.ServerBuilder.

确实NettyServerBuilder 有更丰富的接口，包含了许多设置keepalive 的api 接口。
其中就有限制client 的keepalive 的API，让我们看下源码：

/*** Specify the most aggressive keep-alive time clients are permitted to configure. The server will* try to detect clients exceeding this rate and when detected will forcefully close the* connection. The default is 5 minutes.** <p>Even though a default is defined that allows some keep-alives, clients must not use* keep-alive without approval from the service owner. Otherwise, they may experience failures in* the future if the service becomes more restrictive. When unthrottled, keep-alives can cause a* significant amount of traffic and CPU usage, so clients and servers should be conservative in* what they use and accept.** @see #permitKeepAliveWithoutCalls(boolean)* @since 1.3.0*/public NettyServerBuilder permitKeepAliveTime(long keepAliveTime, TimeUnit timeUnit) {checkArgument(keepAliveTime >= 0, "permit keepalive time must be non-negative: %s",keepAliveTime);permitKeepAliveTimeInNanos = timeUnit.toNanos(keepAliveTime);return this;}

Okay，祝您好运！