Cron

Syntax

# Example of job definition:
# .---------------- minute (0 - 59)
# |  .------------- hour (0 - 23)
# |  |  .---------- day of month (1 - 31)
# |  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...
# |  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# |  |  |  |  |
# *  *  *  *  * user-name  command to be executed

Scheduling Tricks

every Thursday at 3 p.m

00 15 * * Thu /usr/local/bin/mycronjob.sh

quarterly reports after the end of each quarter (use the first day of the following month)

02 03 1 1,4,7,10 * /usr/local/bin/reports.sh

one minute past every hour between 9:01 a.m. and 5:01 p.m.

01 09-17 * * * /usr/local/bin/hourlyreminder.sh

to run a job every two, three, or four hours. That can be accomplished by dividing the hours by the desired interval, such as */3 for every three hours, or 6-18/3 to run every three hours between 6 a.m. and 6 p.m. Other intervals can be divided similarly; for example, the expression */15 in the minutes position means "run the job every 15 minutes."

*/5 08-18/2 * * * /usr/local/bin/mycronjob.sh

in Docker

dockerfile

FROM node:11.15.0-alpine
RUN apk --no-cache add fetchmail ca-certificates openrc

COPY scripts/fetchmail/config/cron /usr/src/fetchmail.cron
RUN chmod 655 /usr/src/fetchmail.cron

COPY scripts/fetchmail/config/docker-entrypoint.sh /usr/src/docker-entrypoint.sh
RUN chmod 655 /usr/src/docker-entrypoint.sh

ENTRYPOINT ["/usr/src/docker-entrypoint.sh"]

Use apk for installing, upgrading, configuring, and removing apps/programs for an Alpine Linux operating system in a consistent manner.

Install

• fetchmail
• ca-certificates
• openrc

OpenRC is the init system used in alpine. The init system manages the services, startup and shutdown of your computer.

scripts/fetchmail/config/cron

* * * * * node /opt/cxm/app/api/scripts/fetchmail/fetchmailrc.js

scripts/fetchmail/config/docker-entrypoint.sh

#!/usr/bin/env sh
set -eu

crond -b
rc-update add local default
crontab /usr/src/fetchmail.cron

node /opt/cxm/app/api/scripts/fetchmail/fetchmailrc.js
chmod 400 ~/.fetchmailrc

fetchmail -N -f ~/.fetchmailrc --sslcertpath /etc/ssl/certs

• crond -b : run in background
• rc-update : add a service to runlevel
• crontab : add cron to daemon
• fetchmail.js : writes ~/.fetchmailrc file

~/.fetchmailrc

poll imap.gmail.com proto imap:
  uidl # POP3 only
  user "ali.iybar.inbox@gmail.com" pass "MyPassword" preconnect 'echo "$(date) fetching Email" >> /root/.fetchmail.log'
  fastuidl 1 # POP3 only
  keep
  no rewrite
  mda "node /opt/cxm/app/api/scripts/fetchmail/fetchmailmda.js --connector-id 0805fc18-be09-4219-bdae-5db919e99f75"
  ssl

fetchmailmda.js

Script which receives a full Mail object from an IMAP server, parses the headers, content and any attachments and prepares it for the next stage in the process (database/queuing).

This script is called from the `fetchmail` daemon which expects an exit code of `0`. If there are any problems processing an email, a non-zero exit code will mean that the fetchmail daemon will try again in the next pass.

 

async function main() {
  process.stdin.resume();
  process.stdin.setEncoding('utf8');
  const source = process.stdin;

  const mail = await simpleParser(source);
  const mailPayload = toEmailPayload(mail);
...
const name = parseFullName(get(mailPayload, 'from[0].name', ''));

it gets the email, parse and use the parsed payloads to save it