Add retries to sending emails

We have occasional release announcement job failures due to network
issues or other SMTP errors sending the announcement. Most of these
appear to be temporary failures that would be resolved with another
attempt.

This patch adds exponential backoff retries to the sending process to
try to get around these failures.

Change-Id: I70bb470639385caecee7ccfc0e449449bfc9b871
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>

openstack_releases/cmds/mail.py

@@ -22,6 +22,8 @@ import argparse
 import email
 import smtplib
 
+import tenacity
+
 
 def main():
     parser = argparse.ArgumentParser()
@@ -47,9 +49,14 @@ def main():
         msg = email.message_from_file(f)
 
     tolist = [address.strip() for address in msg['to'].split(",")]
+    send_email(server, msg, tolist, user=user, pw=pw, debug=args.verbose)
 
-    server = smtplib.SMTP(server)
-    if args.verbose:
+
+@tenacity.retry(wait=tenacity.wait_exponential,
+                stop=tenacity.stop_after_attempt(4))
+def send_email(smtp_server, msg, tolist, user=None, pw=None, debug=False):
+    server = smtplib.SMTP(smtp_server)
+    if debug:
         server.set_debuglevel(True)
     try:
         if pw:

requirements.txt

@@ -19,6 +19,7 @@ mwclient==0.8.1
 jsonschema>=2.6.0
 twine>=1.13.0
 ruamel.yaml>=0.15
+tenacity>=6.1.0
 
 # For release notes generation.
 Jinja2>=2.6  # BSD License (3 clause)