The failure was observed on peach_pit-tot-chrome-pfq-informational (https://uberchromegw.corp.google.com/i/chromeos.chrome/builders/peach_pit-tot-chrome-pfq-informational/builds/6828) and cyan-tot-chrome-pfq-informational (https://uberchromegw.corp.google.com/i/chromeos.chrome/builders/cyan-tot-chrome-pfq-informational/builds/3189). 

Selected error message:
waiting for compiler_proxy...
compiler proxy (pid=1086) status: http://127.0.0.1:8088 error: failed to connect to backend servers
Traceback (most recent call last):
  File "/home/chrome-bot/goma/goma_ctl.py", line 2455, in <module>
    sys.exit(main())
  File "/home/chrome-bot/goma/goma_ctl.py", line 2450, in main
    goma.Dispatch(sys.argv[1:])
  File "/home/chrome-bot/goma/goma_ctl.py", line 1114, in Dispatch
    self._action_mappings.get(args[0], self._DefaultAction)()
  File "/home/chrome-bot/goma/goma_ctl.py", line 801, in _RestartCompilerProxy
    self._StartCompilerProxy()
  File "/home/chrome-bot/goma/goma_ctl.py", line 621, in _StartCompilerProxy
    self._GenericStartCompilerProxy(ensure=False)
  File "/home/chrome-bot/goma/goma_ctl.py", line 618, in _GenericStartCompilerProxy
    raise Error('Failed to start compiler_proxy successfully.')
__main__.Error: Failed to start compiler_proxy successfully.
ERROR   : Thu Jul  6 16:01:18 PDT 2017
ERROR   :  PGID  PPID   PID     ELAPSED     TIME %CPU COMMAND
ERROR   : Arguments of 10: ./build_packages '--board=peach_pit' '--accept_licenses=@CHROMEOS' '--withdebugsymbols' '--skip_chroot_upgrade' '--noworkon' '--run_goma' '--withevents' '--eventfile=/mnt/host/source/buildbot_archive/peach_pit-tot-chrome-pfq-informational/R61-9719.0.0-b6828/build-events.json' 'virtual/target-os' 'virtual/target-os-dev' 'virtual/target-os-test' 'virtual/target-os-factory' 'virtual/target-os-factory-shim' 'chromeos-base/autotest-all'
ERROR   : Backtrace:  (most recent call is last)
ERROR   :  build_packages:307:main(), called: die_err_trap  
ERROR   : 
ERROR   : Command failed:
ERROR   :   Command '( if [[ "${FLAGS_run_goma}" -eq "${FLAGS_TRUE}" ]]; then
ERROR   :     info "Starting goma compiler_proxy."; goma_ctl="${GOMA_DIR:-${HOME}/goma}/goma_ctl.py"; "${goma_ctl}" restart; trap "'${goma_ctl}' stop" EXIT;
ERROR   : fi; set -o pipefail; sudo -E "${EMERGE_CMD[@]}" "${EMERGE_FLAGS[@]}" "${PACKAGES[@]}" | tee "${tmpfile}" )' exited with nonzero code: 1

@@@STEP_FAILURE@@@
16:01:18: ERROR: ./build_packages failed (code=1)

infra issue?