Adds inter-service OpenTracing propagation

This change allows the GitLab rails and sidekiq components to receive
tracing spans from upstream services such as Workhorse and pass these
spans on to downstream services including Gitaly and Sidekiq.

This change will also emit traces for incoming and outgoing requests
using the propagated trace information. This will allow operators and
engineers to view traces across the Workhorse, GitLab Rails, Sidekiq and
Gitaly components.

Additional intra-service instrumentation will be added in future
changes.

1 files changed, 8 insertions, 1 deletions

diff --git a/lib/gitlab/gitaly_client.rb b/lib/gitlab/gitaly_client.rb
index 8bf8a3b53cd..85afbd85fe6 100644
--- a/lib/gitlab/gitaly_client.rb
+++ b/lib/gitlab/gitaly_client.rb
@@ -52,11 +52,18 @@ module Gitlab
           klass = stub_class(name)
           addr = stub_address(storage)
           creds = stub_creds(storage)
-          klass.new(addr, creds)
+          klass.new(addr, creds, interceptors: interceptors)
         end
       end
     end
 
+    def self.interceptors
+      return [] unless Gitlab::Tracing.enabled?
+
+      [Gitlab::Tracing::GRPCInterceptor.instance]
+    end
+    private_class_method :interceptors
+
     def self.stub_cert_paths
       cert_paths = Dir["#{OpenSSL::X509::DEFAULT_CERT_DIR}/*"]
       cert_paths << OpenSSL::X509::DEFAULT_CERT_FILE if File.exist? OpenSSL::X509::DEFAULT_CERT_FILE