Add grpc.log for Gitaly

config/initializers/grpc.rb

+require 'logger'
+
+GRPC_LOGGER = Logger.new(Rails.root.join('log/grpc.log'))
+GRPC_LOGGER.level = ENV['GRPC_LOG_LEVEL'].presence || 'WARN'
+GRPC_LOGGER.progname = 'GRPC'
+
+module GRPC
+  def self.logger
+    GRPC_LOGGER
+  end
+end

doc/administration/gitaly/index.md

@@ -32,6 +32,14 @@ prometheus_listen_addr = "localhost:9236"
 Changes to `/home/git/gitaly/config.toml` are applied when you run `service
 gitlab restart`.
 
+## Client-side GRPC logs
+
+Gitaly uses the [gRPC](https://grpc.io/) RPC framework. The Ruby gRPC
+client has its own log file which may contain useful information when
+you are seeing Gitaly errors. You can control the log level of the
+gRPC client with the `GRPC_LOG_LEVEL` environment variable. The
+default level is `WARN`.
+
 ## Running Gitaly on its own server
 
 > This is an optional way to deploy Gitaly which can benefit GitLab