tracing: Add OpenTracing support

Add OpenTracing [1] support using Jaeger [2]. Introduces two new gRPC
API calls to enable and disable tracing dynamically: `StartTracing()`
and `StopTracing()`.

Full details of this feature are provided in `TRACING.md`.

Updated vendoring for github.com/mdlayher/vsock to resolve hangs using a
vsock socket with `grpcServer.Serve()`. Changes:

    498f144 Handle return result in Accept test
    fda437e Fix unblocking after closing listener
    4b12813 Add go.mod
    ce2ff06 vsock: factor out newConn function on Linux
    d8b0f13 vsock: adjust listener test for nonblocking
    7a158c6 vsock: enable timeouts also on listener connections
    f68ad55 vsock: allow timeouts with Go 1.11
    d0067a6 vsock/conn: don't use struct embedding

Note: the agent **must** be built with golang 1.11* or newer to ensure
correct behaviour.

Fixes kata-containers#322.

[1] - https://opentracing.io
[2] - https://jaegertracing.io

Signed-off-by: James O. D. Hunt <james.o.hunt@intel.com>

Gopkg.toml

@@ -8,7 +8,7 @@
 
 [[constraint]]
   name = "github.com/mdlayher/vsock"
-  revision = "738c88d6e4cfd60e8124a5344fa10d205fd828b9"
+  revision = "676f733b747cd6406f297a51bd086ee8ec8abdbe"
 
 [[constraint]]
   name = "github.com/opencontainers/runc"
@@ -46,6 +46,11 @@
   name = "github.com/containerd/console"
   revision = "2748ece16665b45a47f884001d5831ec79703880"
 
+[[constraint]]
+  name = "github.com/uber/jaeger-client-go"
+  version = "2.15.0"
+
+
 [prune]
   non-go = true
   go-tests = true

Makefile

@@ -11,9 +11,36 @@ PREFIX := /usr
 BINDIR := $(PREFIX)/bin
 # Define if agent will be installed as init
 INIT := no
+
+# Set to "yes" if agent should support OpenTracing with http://jaegertracing.io.
+TRACE := no
+
+# Tracing cannot currently be supported when running the agent as PID 1 since
+# the tracing requires additional services to be started _before_ the agent
+# process starts.
+#
+# These services are required since Jaeger does not currently support VSOCK.
+# Once Jaeger does support VSOCK, this limitation can be removed as the
+# additional services will no longer be required.
+#
+# See TRACING.md for further details.
+ifeq ($(TRACE),yes)
+  ifeq ($(INIT),yes)
+    $(error ERROR: "TRACE=yes" requires "INIT=no")
+  endif
+endif
+
+# If "yes", install additional services to redirect guest OS journal messages
+# to the host using VSOCK.
+TRACE_DEV_MODE := no
+
 # Path to systemd unit directory if installed as not init.
 UNIT_DIR := /usr/lib/systemd/system
 
+# Path to systemd drop-in snippet directory used to override the agent's
+# service without having to modify the pristine agent service file.
+SNIPPET_DIR := /etc/systemd/system/$(AGENT_SERVICE).d/
+
 GENERATED_FILES :=
 
 ifeq ($(INIT),no)
@@ -24,6 +51,15 @@ ifeq ($(INIT),no)
     UNIT_FILES += kata-containers.target
 endif
 
+ifeq ($(TRACE),yes)
+    UNIT_FILES += jaeger-client-socat-redirector.service
+endif
+
+ifeq ($(TRACE_DEV_MODE),yes)
+    UNIT_FILES += kata-journald-host-redirect.service
+    SNIPPET_FILES += kata-redirect-agent-output-to-journal.conf
+endif
+
 VERSION_FILE := ./VERSION
 VERSION := $(shell grep -v ^\# $(VERSION_FILE))
 COMMIT_NO := $(shell git rev-parse HEAD 2> /dev/null || true)
@@ -56,6 +92,11 @@ ifeq ($(INIT),no)
 	@echo "Installing systemd unit files..."
 	$(foreach f,$(UNIT_FILES),$(call INSTALL_FILE,$f,$(UNIT_DIR)))
 endif
+ifeq ($(TRACE_DEV_MODE),yes)
+	@echo "Installing systemd snippet files..."
+	@mkdir -p $(SNIPPET_DIR)
+	$(foreach f,$(SNIPPET_FILES),$(call INSTALL_FILE,$f,$(SNIPPET_DIR)))
+endif
 
 build-image:
 	# build an docker image for development

README.md

@@ -5,6 +5,7 @@
 
 * [Debug mode](#debug-mode)
 * [Developer mode](#developer-mode)
+* [Enable trace support](#enable-trace-support)
 
 This project implements an agent called `kata-agent` that runs inside a virtual machine (VM).
 
@@ -22,3 +23,7 @@ See the [developer guide](https://github.com/kata-containers/documentation/blob/
 Add `agent.devmode` to the guest kernel command line to allow the agent
 process to coredump (disabled by default). Specifying this option implicitly
 enables [debug mode](#debug-mode).
+
+## Enable trace support
+
+See [the tracing guide](TRACING.md).