redis_cron

redis_cron is a simple cron expression based job scheduler for Redis that runs inside redis as a module. It uses similar syntax as a regular cron and allows you to schedule redis commands directly on redis. This project is inspired from PostgreSQL extension pg_cron.

redis_cron runs scheduled jobs sequentially in a single thread since redis commands can only be run by one thread at a time inside redis.

Install

$ cargo build
$ # Mac:
$ redis-server --loadmodule ./target/debug/libredis_cron.dylib
$ # Linux:
$ redis-server --loadmodule ./target/debug/libredis_cron.so

Usage

Available commands:

CRON.SCHEDULE <cron-expression> <redis-command>
CRON.UNSCHEDULE <job-id>
CRON.LIST

Example

$ redis-cli
127.0.0.1:6379> CRON.SCHEDULE "1/10 * * * * *" EVAL "return redis.call('set','foo','bar')" 0
"f04fefb1-ebf1-4d47-a582-f04963df994b"
127.0.0.1:6379> CRON.SCHEDULE "1/5 * * * * *" HINCRBY myhash field 1
"be428e43-5501-4eed-83c3-2c9ef3c52f6f"
127.0.0.1:6379> CRON.LIST
1) 1) f04fefb1-ebf1-4d47-a582-f04963df994b
   2) 1/10 * * * * *
   3) EVAL return redis.call('set','foo','bar') 0
2) 1) be428e43-5501-4eed-83c3-2c9ef3c52f6f
   2) 1/5 * * * * *
   3) HINCRBY myhash field 1
127.0.0.1:6379> CRON.UNSCHEDULE be428e43-5501-4eed-83c3-2c9ef3c52f6f
(integer) 1
127.0.0.1:6379> CRON.LIST
1) 1) f04fefb1-ebf1-4d47-a582-f04963df994b
   2) 1/10 * * * * *
   3) EVAL return redis.call('set','foo','bar') 0
127.0.0.1:6379> CRON.UNSCHEDULE f04fefb1-ebf1-4d47-a582-f04963df994b
(integer) 1
127.0.0.1:6379> CRON.LIST
(empty array)

Logs:

66004:M 06 Mar 2021 15:33:22.814 # Server initialized
66004:M 06 Mar 2021 15:33:22.815 * Module 'cron' loaded from ./target/debug/libredis_cron.dylib
66004:M 06 Mar 2021 15:33:22.815 * Ready to accept connections
66004:M 06 Mar 2021 15:34:01.462 * <module> redis_cron: run: job_id=f04fefb1-ebf1-4d47-a582-f04963df994b; schedule=1/10 * * * * *; cmd=EVAL;
66004:M 06 Mar 2021 15:34:06.486 * <module> redis_cron: run: job_id=be428e43-5501-4eed-83c3-2c9ef3c52f6f; schedule=1/5 * * * * *; cmd=HINCRBY;
66004:M 06 Mar 2021 15:34:11.000 * <module> redis_cron: run: job_id=f04fefb1-ebf1-4d47-a582-f04963df994b; schedule=1/10 * * * * *; cmd=EVAL;
66004:M 06 Mar 2021 15:34:11.000 * <module> redis_cron: run: job_id=be428e43-5501-4eed-83c3-2c9ef3c52f6f; schedule=1/5 * * * * *; cmd=HINCRBY;
66004:M 06 Mar 2021 15:34:16.017 * <module> redis_cron: run: job_id=be428e43-5501-4eed-83c3-2c9ef3c52f6f; schedule=1/5 * * * * *; cmd=HINCRBY;
66004:M 06 Mar 2021 15:34:21.043 * <module> redis_cron: run: job_id=f04fefb1-ebf1-4d47-a582-f04963df994b; schedule=1/10 * * * * *; cmd=EVAL;
66004:M 06 Mar 2021 15:34:21.043 * <module> redis_cron: run: job_id=be428e43-5501-4eed-83c3-2c9ef3c52f6f; schedule=1/5 * * * * *; cmd=HINCRBY;
66004:M 06 Mar 2021 15:34:26.069 * <module> redis_cron: run: job_id=be428e43-5501-4eed-83c3-2c9ef3c52f6f; schedule=1/5 * * * * *; cmd=HINCRBY;
66004:M 06 Mar 2021 15:34:31.086 * <module> redis_cron: run: job_id=f04fefb1-ebf1-4d47-a582-f04963df994b; schedule=1/10 * * * * *; cmd=EVAL;
66004:M 06 Mar 2021 15:34:41.116 * <module> redis_cron: run: job_id=f04fefb1-ebf1-4d47-a582-f04963df994b; schedule=1/10 * * * * *; cmd=EVAL;

Cron expression syntax

Creating a schedule for a job is done using the FromStr impl for the Schedule type of the cron library.

The scheduling format is as follows:

sec   min   hour   day of month   month   day of week   year
*     *     *      *              *       *             *

Time is specified for UTC and not your local timezone. Note that the year may be omitted.

Comma separated values such as 5,8,10 represent more than one time value. So for example, a schedule of 0 2,14,26 * * * * would execute on the 2nd, 14th, and 26th minute of every hour.

Ranges can be specified with a dash. A schedule of 0 0 * 5-10 * * would execute once per hour but only on day 5 through 10 of the month.

Day of the week can be specified as an abbreviation or the full name. A schedule of 0 0 6 * * Sun,Sat would execute at 6am on Sunday and Saturday.

Reference

This project uses makes use of redismodule-rs