I hope who ever is reading this is doing well.

Here's a scenario that I'm wondering about: there's a global ClientConn that is being used for all grpc requests to a server. Then that server goes down. I was wondering if there's a way to wait for this server to go up with some timeout in order for the usage of grpc in this scenario to be more resilient to failures(either a transient failure or server goes down). I was thinking keep looping if the clientConn state is connecting or a transient failure and if a timeout occurs when the clientConn state was a transient failure then return an error since the server might be down.

I was wondering if this would work if there are multiple requests coming in the client side that would need this ClientConn so then multiple go routines would be running this loop. Would appreciate any other alternatives, suggestions, or advice.

CodePudding user response：

When you call grpc.Dial to connect to a server and receive a grpc.ClientConn, it will automatically handle reconnections for you. When you call a method or request a stream, it will fail if it can't connect to the server or if there is an error processing the request.

You could retry a few times if the error indicates that it is due to the network. You can check the grpc status codes in here https://github.com/grpc/grpc-go/blob/master/codes/codes.go#L31 and extract them from the returned error using status.FromError: https://pkg.go.dev/google.golang.org/grpc/status#FromError

You also have the grpc.WaitForReady option (https://pkg.go.dev/google.golang.org/grpc#WaitForReady) which can be used to block the grpc call until the server is ready if it is in a transient failure. In that case, you don't need to retry, but you should probably add a timeout that cancels the context to have control over how long you stay blocked.

If you want to even avoid trying to call the server, you could use ClientConn.WaitForStateChange (which is experimental) to detect any state change and call ClientConn.GetState to determine in what state is the connection to know when it is safe to start calling the server again.