Ruby - Execution expired

I have a ruby code like this:

begin
  doc = Nokogiri::HTML(open(url).read.strip)
rescue Exception => ex
  log.error "Error: #{ex}"
end

And I am getting log as:

ERROR -- : Error: execution expired

I want block re-execute until it success.

How can I do it?

I'll expand on my comment a little bit. You can use retry to go back to the begin:

begin
  doc = Nokogiri::HTML(open(url).read.strip)
rescue Exception => ex
  log.error "Error: #{ex}"
  retry
end

That will keep trying (and logging errors) until it works or you manually kill it. That's probably not what you want though as one little mistake will send you into an infinite loop. An easy way around that is to let it try for, say, 10 times and then give up:

MAX_ATTEMPTS = 10

doc = nil
begin
  doc = Nokogiri::HTML(open(url).read.strip)
rescue Exception => ex
  log.error "Error: #{ex}"
  attempts = attempts + 1
  retry if(attempts < MAX_ATTEMPTS)
end

if(doc.nil?)
  # Do something about the persistent error
  # so that you don't try to access a nil
  # doc later on.
end

Something like this will try a few times and then give up. You could also put a sleep call before the retry if you want to wait a bit before the next attempt or investigate the exception (possibly with multiple rescue blocks) to choose if you should give up immediately, wait and retry, or retry immediately.