qron

Qron

Qron is a simple scheduler for message queues.

Install

Download the latest release binary.

Or use go tool. This will install the qron binary to your $GOPATH/bin:

$ go get github.com/mak73kur/qron/cmd/qron

Usage

Run qron (in a verbose mode):

$ qron -c /path/to/config.yml -v

Example config:

reader:
    type: inline
    tab: |
        * * * * * every minute

writer:
    type: log

There are two main sections:

• reader which tells qron where should it look for a job schedule called qron tab.
• writer that decides where to qron will publish messages.

Specific properties depend on the chosen reader and writer types.

Thanks to spf13/viper, config file supports different formats: json, toml, yaml.

If path argument is empty, qron will try ./qron.yml by default.

Qron tab

Each line is a new job.

Parameters should be separated by a single whitespace character.

First five are schedule parameters, sixth is a message body. Another optional parameter is tags, see below.

Message body can have whitespace or any other character, except newline.

┌───────────── min (0-59)
│ ┌────────────── hour (0-23)
│ │ ┌─────────────── day of month (1-31)
│ │ │ ┌──────────────── month (1-12)
│ │ │ │ ┌───────────────── day of week (0-6) (0 to 6 are Sunday to Saturday)
│ │ │ │ │
│ │ │ │ │
* * * * * message_body

Allowed parameter expressions:

• asterisk(*) — anything passes.
• comma(,) — 0 5,17 * * 1 — executes at 5AM and 5PM each Monday.
• slash(/) — 0 */6 * * * — shortcut for 0,6,12,18.

Qron will skip any lines that are empty or start with the comment characters (# or //).

Message can be followed by tag options for this job - JSON object enclosed in back quotes e.g. `{"ttl":"1m","key":"qron2"}`.

Actual effect (if any) of these tags ensured by the writer implementation.

Qron tab readers

Tab can be loaded from one of the following sources.

Inline source

Store the tab directly in the same config.

reader:
    type: inline
    tab: |
        * * * * * every minute
        */2 * * * * every two minutes

File source

The file will be read once on program start. Sending SIGHUP will trigger file reread without a restart (this is also true for redis reader).

reader:
    type: file
    path: /tmp/qrontab

Redis source

Tab is stored as a single string value in Redis DB.

Separate program thread will call GET <key> every minute to update the tab on any changes.

Note: if the value gets cleared for some reason - qron will assume the tab is empty and will continue to run with nothing to publish.

reader:
    type: redis
    url: localhost:6379
    key: qrontab
    # optional, 0 by default
    db: 0
    # optional, redis auth password
    auth: secret

Writers

Every minute qron checks whether a job matches the current time. If it does — qron writer will publish the job message.

Log writer

For debug purposes. Writes message directly to the program output.

writer.type: log

AMQP writer

AMQP writes messages to RabbitMQ or any other protocol implementation.

writer:
    type: amqp
    url: amqp://localhost:5672
    exchange: ""
    key: qron

AMQP handles two tag options:

• key - overrides routing key for this message.
• ttl - message expiration, see rabbitmq docs; ttl value can be either number of seconds or string duration, such as 2h45m30s.

* * * * * every minute `{"ttl":"1m","key":"ticker"}`

Redis writer

Push messages into the Redis list. Consumer side can use BRPOP or BLPOP to receive them.

writer:
    type: redis
    url: localhost:6379
    key: qron
    # optional, 0 by default
    db: 1
    # optional, redis auth password
    auth: secret
    # optionaly use LPUSH, default is RPUSH
    lpush: true

Redis supports key tag to override list key for any given job.

* * * * * every minute `{"key":"ticker"}`

HTTP writer

Send messages as HTTP requests.

writer:
    type: http
    url: https://destination-site.com/consume
    method: POST
    headers:
        X-Auth: "token"
        Content-Type: "application/x-www-form-urlencoded"

HTT supports url, method and headers tags to override URL or add headers for any given job.

* * * * * every=minute `{ "headers": {"X-Auth":"token2"} }`

TODO

• verbose mode
• custom msg options
• proper godoc
• tests for the base package