cron-job.org

Structure

• database contains the MySQL database structure.
• chronos is cron-job.org's cron job execution daemon and is responsible for fetching the jobs.
• protocol contains the interface definitions for interaction between system nodes.
• frontend contains the web interface
• statuspage contains the status page UI
• api contains the server API used by web interface and status page UI.

chronos

Concept

chronos checks the MySQL database every minute to collect all jobs to execute. For every minute, a thread is spawned which processes all the jobs. Actual HTTP fetching is done using the excellent curl multi library with libev as library used to provide the event loop. Together with the c-ares resolver this allows for thousands of parallel HTTP requests.

cron-job.org supports storing the job results for the user's convenience. This can quickly lead to I/O bottlenecks when storing the result data in a MySQL database. (Which also has the downside that cleaning up old entries is extremely expensive.) To solve this issue, chronos stores the results in per-user per-day SQLite databases. Cleaning up old entries is as easy as deleting the corresponding day's databases.

The whole software is optimized on performance rather than on data integrity, i.e. when your server crashes or you have a power outage / hardware defect, the job history is most likely lost. Since this is volatile data anyway, it's not considered a big issue.

chronos can now run on multiple nodes. Each node requires an own MySQL server/database and stores its own jobs. The host running the web interface also manages the user database and an association between job and node. The web interface can create, delete, update and fetch jobs and job logs from the particular node via a Thrift-based protocol defined in the protocol folder.

Prerequisites

In order to build chronos, you need development files of:

• curl (preferably with c-ares as resolver and libidn2 for IDN support)
• libev
• mysqlclient
• sqlite3
• thrift (compiler and libthrift)

To build, you need a C++14 compiler and cmake.

Building

1. Create and enter a build folder: mkdir build && cd build
2. Run cmake: cmake -DCMAKE_BUILD_TYPE=Release ..
3. Build the project: make

Running

1. Ensure you've imported the DB scheme from the database folder
2. Customize chronos.cfg according to your system (especially add your MySQL login)
3. Execute ./chronos /path/to/chronos.cfg

API

The API is written in PHP and needs to be hosted on a webserver (cron-job.org uses nginx with php-fpm). It is used by the console and the status page UI.

Prerequisites

• nginx with php-fpm (PHP 7)
• Optionally, a redis instance to support API call rate limiting

Getting started

• Copy the api/ folder to your webserver
• Create a copy of config/config.inc.default.php as lib/config.inc.php and customize it according to your environment

Notes

• When changing the thrift protocol, don't forget to re-compile the PHP glue code and copy it to lib/protocol/. When committing, include the updated PHP code. Currently, this is a manual step.

Frontend

The frontend is written in JavaScript using React and material-ui. You need npm to build it.

Prerequisites

• Node.js

Getting started

• Go to the frontend/ folder
• Install all required dependencies by running npm install
• Create a copy of src/utils/Config.default.js as src/utils/Config.js and customize it according to your environment
• Run the web interface via npm start

Status Page Frontend

The status page frontend is written in JavaScript using React and material-ui. You need npm to build it.

Prerequisites

• Node.js

Getting started

• Go to the statuspage/ folder
• Install all required dependencies by running npm install
• Create a copy of src/utils/Config.default.js as src/utils/Config.js and customize it according to your environment
• Run the web interface via npm start

Example Environment (using Docker Compose)

To quickly start an example environment of most of the cron-job.org system, you can use docker-compose:

• Initialize/update submodules: git submodule init && git submodule update
• Copy .env.example to .env and open it in a text editor
• Change the variables in .env as desired. As an absolute minimum, fill the *_SECRET variables with randomly generated secrets and specify a SMTP server in SMTP_SERVER. No authentication is used for the SMTP session, so ensure that the SMTP server is allowing relaying for your machine's IP address.
• Start via docker compose up and wait until all containers are built and all services have been started. This can take a while, especially on first run.
• Open http://localhost:8010/ in your browser (assuming you kept the default port and host name settings).

Important: The Docker environment contained in this repo is intended as an example / development environment and is not tailored for production usage, especially with regard to security.

The following containers will be started:

• mysql-master for the master service database which also stores users, groups, job -> node associations etc.
• mysql-node for the node service database. Used to store per-executor information like job details with their schedules, etc.
• redis used as a cache for certain features like rate limiting.
• api for the PHP-based API backend used by the frontend. Uses php-fpm.
• frontend which hosts the built frontend code.
• wwww as the frontend nginx-powered HTTP server which connects to frontend (HTTP reverse proxy) and api (FastCGI).
• chronos which runs chronos in a combined master and node service mode.

General notes

• We strongly recommend to build curl using the c-ares resolver. Otherwise every request might spawn its own thread for DNS resolving and your machine will run out of resources very soon.
• Before running chronos, ensure that the limit of open files/sockets is not set too low. You might want to run ulimit -n 65536 or similar first.
• If data integrity is not important for you, we highly recommend to set innodb_flush_log_at_trx_commit=0 and innodb_flush_method=O_DIRECT in your MySQL config for best performance. Otherwise the update thread (which is responsible for storing the job resuls) might lag behind the actual job executions quite soon.
• Parts of the source are quite old and from early stages of the project and might require a refactoring sooner or later.