Check status of some web services and send an email if they're down

check

#!/usr/bin/env python
# check - Check status of some web services
# and send an email if they're down.

# List of checks to perform. Tuples in the form
# (url, expected_http_response)
sender = 'noreply@example.com'
recipient = 'root@example.com'
subject = 'Checks Failed'
mailserver = 'localhost'

DEBUG = False
CACHE = '/tmp/check-py-services'

checks = [
  ('http://example.com', 200),
]

import sys
import threading
import urllib2
import smtplib
from email.mime.text import MIMEText

threads = []
results = []


def log(message):
  if DEBUG:
    print message

def check_status(url, expect):
  global results

  log("[%s] Checking" % (url))

  try:
    conn = urllib2.urlopen(url, timeout=5)
    conn.close()
    result = conn.getcode()

  except urllib2.URLError:
    # Typically a timeout
    result = 'timeout'

  log("[%s] got %s" % (url, result))

  results.append({
    'url': url,
    'code': result,
    'expect': expect,
    'result': (result == expect),
  })

# Perform the checks in parallel
for check in checks:
  thread = threading.Thread(target=check_status, args=check)
  thread.start()
  threads.append(thread)

# Wait for them all to finish
for thread in threads:
  thread.join()

log("Finished")

# If any results are False
failures = filter(lambda result: result['result'] == False, results)

# None found, nothing to do here
if not failures:
  sys.exit(0)

log("Oops, something appears to be down. Notifying %s" % recipient)
downed_service_message = "\n".join([ " * %s returned %s" % (result['url'], result['code']) for result in failures])

# Check if this is the same as the list we had last time
# If it is, exit gracefully

# Just in case
open(CACHE, 'a').close()

with open(CACHE, 'r') as file:
  cache = file.read()
  if cache == downed_service_message:
    sys.exit(0)

# If not, update the cached list and send the email
with open(CACHE, 'w') as file:
  file.write(downed_service_message)

message = MIMEText("""Hello,

While performing automated checks, the following services were detected
to be in incorrect states:

%s

Cheers,
check.py robot
""" % downed_service_message)

message['Subject'] = subject
message['From'] = sender
message['To'] = recipient
message['X-Mailer'] = 'HTTP Services Checker <me@lewiseason.co.uk>'

s = smtplib.SMTP(mailserver)
s.sendmail(sender, [recipient], message.as_string())
s.quit()