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Tempo: Fix grpc streaming support over pdc-agent (#89883)

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* Tempo: Fix grpc streaming support over pdc-agent

* Fix a spelling error and formatting

* Ignore lint issue for reasons listed in source code comment

---------

Co-authored-by: Joey Tawadrous <joey.tawadrous@grafana.com>
This commit is contained in:
Taylor Dean 2024-07-04 09:09:34 -04:00 committed by GitHub
parent 12a5583eb6
commit d5b21f77aa
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1 changed files with 22 additions and 1 deletions
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23
pkg/tsdb/tempo/grpc.go
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@ -48,7 +48,28 @@ func newGrpcClient(ctx context.Context, settings backend.DataSourceInstanceSetti
if err != nil {
return nil, fmt.Errorf("error getting dial options: %w", err)
}
clientConn, err := grpc.NewClient(onlyHost, dialOpts...)
// grpc.Dial() is deprecated in favor of grpc.NewClient(), but grpc.NewClient() changed the default resolver to dns from passthrough.
// This is a problem because the getDialOpts() function appends a custom dialer to the dial options to support Grafana Cloud PDC.
//
// See the following quote from the grpc package documentation:
// One subtle difference between NewClient and Dial and DialContext is that the
// former uses "dns" as the default name resolver, while the latter use
// "passthrough" for backward compatibility. This distinction should not matter
// to most users, but could matter to legacy users that specify a custom dialer
// and expect it to receive the target string directly.
// https://github.com/grpc/grpc-go/blob/fa274d77904729c2893111ac292048d56dcf0bb1/clientconn.go#L209
//
// Unfortunately, the passthrough resolver isn't exported by the grpc package, so we can't use it.
// The options are to continue using grpc.Dial() or implement a custom resolver.
// Since the go-grpc package maintainers intend to continue supporting grpc.Dial() through the 1.x series,
// we'll continue using grpc.Dial() until we have a compelling reason or bandwidth to implement the custom resolver.
// Reference: https://github.com/grpc/grpc-go/blob/f199062ef31ddda54152e1ca5e3d15fb63903dc3/clientconn.go#L204
//
// See this issue for more information: https://github.com/grpc/grpc-go/issues/7091
// Ignore the lint check as this fails the build and for the reasons above.
// nolint:staticcheck
clientConn, err := grpc.Dial(onlyHost, dialOpts...)
if err != nil {
logger.Error("Error dialing gRPC client", "error", err, "URL", settings.URL, "function", logEntrypoint())
return nil, err