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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,206 @@ | ||
| ## Anti-Patterns | ||
|
|
||
| ### Dialing in gRPC | ||
| [`grpc.Dial`](https://pkg.go.dev/google.golang.org/grpc#Dial) is a function in | ||
| the gRPC library that creates a virtual connection from the gRPC client to the | ||
| gRPC server. It takes a target URI (which can represent the name of a logical | ||
| backend service and could resolve to multiple actual addresses) and a list of | ||
| options, and returns a | ||
| [`ClientConn`](https://pkg.go.dev/google.golang.org/grpc#ClientConn) object that | ||
| represents the connection to the server. The `ClientConn` contains one or more | ||
| actual connections to real server backends and attempts to keep these | ||
| connections healthy by automatically reconnecting to them when they break. | ||
|
|
||
| The `Dial` function can also be configured with various options to customize the | ||
| behavior of the client connection. For example, developers could use options | ||
| such a | ||
| [`WithTransportCredentials`](https://pkg.go.dev/google.golang.org/grpc#WithTransportCredentials) | ||
| to configure the transport credentials to use. | ||
|
|
||
| While `Dial` is commonly referred to as a "dialing" function, it doesn't | ||
| actually perform the low-level network dialing operation like | ||
| [`net.Dial`](https://pkg.go.dev/net#Dial) would. Instead, it creates a virtual | ||
| connection from the gRPC client to the gRPC server. | ||
|
|
||
| `Dial` does initiate the process of connecting to the server, but it uses the | ||
| ClientConn object to manage and maintain that connection over time. This is why | ||
| errors encountered during the initial connection are no different from those | ||
| that occur later on, and why it's important to handle errors from RPCs rather | ||
| than relying on options like | ||
| [`FailOnNonTempDialError`](https://pkg.go.dev/google.golang.org/grpc#FailOnNonTempDialError), | ||
| [`WithBlock`](https://pkg.go.dev/google.golang.org/grpc#WithBlock), and | ||
| [`WithReturnConnectionError`](https://pkg.go.dev/google.golang.org/grpc#WithReturnConnectionError). | ||
| In fact, `Dial` does not always establish a connection to servers by default. | ||
| The connection behavior is determined by the load balancing policy being used. | ||
| For instance, an "active" load balancing policy such as Round Robin attempts to | ||
| maintain a constant connection, while the default "pick first" policy delays | ||
| connection until an RPC is executed. Instead of using the WithBlock option, which | ||
| may not be recommended in some cases, you can call the | ||
| [`ClientConn.Connect`](https://pkg.go.dev/google.golang.org/grpc#ClientConn.Connect) | ||
| method to explicitly initiate a connection. | ||
|
|
||
| ### Using `FailOnNonTempDialError`, `WithBlock`, and `WithReturnConnectionError` | ||
|
|
||
| The gRPC API provides several options that can be used to configure the behavior | ||
| of dialing and connecting to a gRPC server. Some of these options, such as | ||
| `FailOnNonTempDialError`, `WithBlock`, and `WithReturnConnectionError`, rely on | ||
| failures at dial time. However, we strongly discourage developers from using | ||
| these options, as they can introduce race conditions and result in unreliable | ||
| and difficult-to-debug code. | ||
|
|
||
| One of the most important reasons for avoiding these options, which is often | ||
| overlooked, is that connections can fail at any point in time. This means that | ||
| you need to handle RPC failures caused by connection issues, regardless of | ||
| whether a connection was never established in the first place, or if it was | ||
| created and then immediately lost. Implementing proper error handling for RPCs | ||
| is crucial for maintaining the reliability and stability of your gRPC | ||
| communication. | ||
|
|
||
| ### Why we discourage using `FailOnNonTempDialError`, `WithBlock`, and `WithReturnConnectionError` | ||
|
|
||
| When a client attempts to connect to a gRPC server, it can encounter a variety | ||
| of errors, including network connectivity issues, server-side errors, and | ||
| incorrect usage of the gRPC API. The options `FailOnNonTempDialError`, | ||
| `WithBlock`, and `WithReturnConnectionError` are designed to handle some of | ||
| these errors, but they do so by relying on failures at dial time. This means | ||
| that they may not provide reliable or accurate information about the status of | ||
| the connection. | ||
|
|
||
| For example, if a client uses `WithBlock` to wait for a connection to be | ||
| established, it may end up waiting indefinitely if the server is not responding. | ||
| Similarly, if a client uses `WithReturnConnectionError` to return a connection | ||
| error if dialing fails, it may miss opportunities to recover from transient | ||
| network issues that are resolved shortly after the initial dial attempt. | ||
|
|
||
| ## Best practices for error handling in gRPC | ||
|
|
||
| Instead of relying on failures at dial time, we strongly encourage developers to | ||
| rely on errors from RPCs. When a client makes an RPC, it can receive an error | ||
| response from the server. These errors can provide valuable information about | ||
| what went wrong, including information about network issues, server-side errors, | ||
| and incorrect usage of the gRPC API. | ||
|
|
||
| By handling errors from RPCs correctly, developers can write more reliable and | ||
| robust gRPC applications. Here are some best practices for error handling in | ||
| gRPC: | ||
|
|
||
| - Always check for error responses from RPCs and handle them appropriately. | ||
| - Use the `status` field of the error response to determine the type of error that | ||
| occurred. | ||
| - When retrying failed RPCs, consider using the built-in retry mechanism | ||
| provided by gRPC-Go, if available, instead of manually implementing retries. | ||
| Refer to the [gRPC-Go retry example | ||
| documentation](https://github.com/grpc/grpc-go/blob/master/examples/features/retry/README.md) | ||
| for more information. | ||
| - Avoid using `FailOnNonTempDialError`, `WithBlock`, and | ||
| `WithReturnConnectionError`, as these options can introduce race conditions and | ||
| result in unreliable and difficult-to-debug code. | ||
| - If making the outgoing RPC in order to handle an incoming RPC, be sure to | ||
| translate the status code before returning the error from your method handler. | ||
| For example, if the error is an `INVALID_ARGUMENT` error, that probably means | ||
| your service has a bug (otherwise it shouldn't have triggered this error), in | ||
| which case `INTERNAL` is more appropriate to return back to your users. | ||
|
|
||
| ### Example: Handling errors from an RPC | ||
|
|
||
| The following code snippet demonstrates how to handle errors from an RPC in | ||
| gRPC: | ||
|
|
||
| ```go | ||
| ctx, cancel := context.WithTimeout(context.Background(), time.Second) | ||
| defer cancel() | ||
|
|
||
| res, err := client.MyRPC(ctx, &MyRequest{}) | ||
| if err != nil { | ||
| // Handle the error appropriately, | ||
| // log it & return an error to the caller, etc. | ||
| log.Printf("Error calling MyRPC: %v", err) | ||
| return nil, err | ||
| } | ||
|
|
||
| // Use the response as appropriate | ||
| log.Printf("MyRPC response: %v", res) | ||
| ``` | ||
|
|
||
| To determine the type of error that occurred, you can use the status field of | ||
| the error response: | ||
|
|
||
|
|
||
| ```go | ||
| resp, err := client.MakeRPC(context.Background(), request) | ||
| if err != nil { | ||
| status, ok := status.FromError(err) | ||
| if ok { | ||
| // Handle the error based on its status code | ||
| if status.Code() == codes.NotFound { | ||
| log.Println("Requested resource not found") | ||
| } else { | ||
| log.Printf("RPC error: %v", status.Message()) | ||
| } | ||
| } else { | ||
| //Handle non-RPC errors | ||
| log.Printf("Non-RPC error: %v", err) | ||
| } | ||
| return | ||
| } | ||
|
|
||
| // Use the response as needed | ||
| log.Printf("Response received: %v", resp) | ||
| ``` | ||
|
|
||
| ### Example: Using a backoff strategy | ||
|
|
||
|
|
||
| When retrying failed RPCs, use a backoff strategy to avoid overwhelming the | ||
| server or exacerbating network issues: | ||
|
|
||
|
|
||
| ```go | ||
| var res *MyResponse | ||
| var err error | ||
|
|
||
| // If the user doesn't have a context with a deadline, create one | ||
| ctx, cancel := context.WithTimeout(context.Background(), time.Second) | ||
| defer cancel() | ||
|
|
||
| // Retry the RPC call a maximum number of times | ||
| for i := 0; i < maxRetries; i++ { | ||
|
|
||
| // Make the RPC call | ||
| res, err = client.MyRPC(ctx, &MyRequest{}) | ||
|
|
||
| // Check if the RPC call was successful | ||
| if err == nil { | ||
| // The RPC was successful, so break out of the loop | ||
| break | ||
| } | ||
|
|
||
| // The RPC failed, so wait for a backoff period before retrying | ||
| backoff := time.Duration(i) * time.Second | ||
| log.Printf("Error calling MyRPC: %v; retrying in %v", err, backoff) | ||
| time.Sleep(backoff) | ||
| } | ||
|
|
||
| // Check if the RPC call was successful after all retries | ||
| if err != nil { | ||
| // All retries failed, so handle the error appropriately | ||
| log.Printf("Error calling MyRPC: %v", err) | ||
| return nil, err | ||
| } | ||
|
|
||
| // Use the response as appropriate | ||
| log.Printf("MyRPC response: %v", res) | ||
| ``` | ||
|
|
||
|
|
||
| ## Conclusion | ||
|
|
||
| The | ||
| [`FailOnNonTempDialError`](https://pkg.go.dev/google.golang.org/grpc#FailOnNonTempDialError), | ||
| [`WithBlock`](https://pkg.go.dev/google.golang.org/grpc#WithBlock), and | ||
| [`WithReturnConnectionError`](https://pkg.go.dev/google.golang.org/grpc#WithReturnConnectionError) | ||
| options are designed to handle errors at dial time, but they can introduce race | ||
| conditions and result in unreliable and difficult-to-debug code. Instead of | ||
| relying on these options, we strongly encourage developers to rely on errors | ||
| from RPCs for error handling. By following best practices for error handling in | ||
| gRPC, developers can write more reliable and robust gRPC applications. |
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