Horizon GUI throws 500 error

Issue

• Unable to open the Horizon GUI, it throws 500 code and logs shows below error

  [Wed Aug 01 10:38:08.893718 2018] [:error] [pid 9535] [remote 10.70.56.62:200]     '%r: %s' % (name, e))
  [Wed Aug 01 10:38:08.893732 2018] [:error] [pid 9535] [remote 10.70.56.62:200] ValueError: Unable to configure handler 'file': [Errno 13] Permission denied: '/var/log/horizon/horizon.log'