最近遇到 grpc 客户端报错 rpc error: code = Unavailable desc = transport is closing，原因是连接长时间没有使用，被服务端断开，这种情况通过简单粗暴的重试策略可以解决，更加优雅的解决方案是增加保持连接策略
服务端
var kaep = keepalive.EnforcementPolicy{
MinTime: 5 * time.Second, // If a client pings more than once every 5 seconds, terminate the connection
PermitWithoutStream: true, // Allow pings even when there are no active streams
}
var kasp = keepalive.ServerParameters{
MaxConnectionIdle: 15 * time.Second, // If a client is idle for 15 seconds, send a GOAWAY
MaxConnectionAge: 30 * time.Second, // If any connection is alive for more than 30 seconds, send a GOAWAY
MaxConnectionAgeGrace: 5 * time.Second, // Allow 5 seconds for pending RPCs to complete before forcibly closing connections
Time: 5 * time.Second, // Ping the client if it is idle for 5 seconds to ensure the connection is still active
Timeout: 1 * time.Second, // Wait 1 second for the ping ack before assuming the connection is dead
}
server := grpc.NewServer(grpc.KeepaliveEnforcementPolicy(kaep), grpc.KeepaliveParams(kasp))客户端
var kacp = keepalive.ClientParameters{
Time: 10 * time.Second, // send pings every 10 seconds if there is no activity
Timeout: time.Second, // wait 1 second for ping ack before considering the connection dead
PermitWithoutStream: true, // send pings even without active streams
}
conn, err := grpc.Dial(*addr, grpc.WithInsecure(), grpc.WithKeepaliveParams(kacp))