LATER

Later is a redis base delay queue

Usege

golang version: 1.7+

go build github.com/btfak/later
$: ./later -h
Usage of ./later:
  -address string
    	serve listen address (default ":8080")
  -redis string
    	redis address (default "redis://127.0.0.1:6379/0")

Feature

• Delay push message to target
• At-lease-once delivery
• Fail and retry
• Reliable
• Performance

Frontend API

Response http code: 200 success, 400 request invalid, 404 task not found, 500 internal error

• Create Task

  Request:
  POST /create
  {
  	"topic":"order",
  	"delay":15, // second
  	"retry":3,  // max retry 3 times, interval 10,20,40... seconds
  	"callback":"http://127.0.0.1:8888/", // http post to target url
  	"content":"hello" // content to post
  }
  Response:
  {
      "id": "35adbde5-77c4-4d65-adac-0082d91f2554"
  }
  

• Delete Task

  Request:
  POST /delete
  {
  	"id":"35adbde5-77c4-4d65-adac-0082d91f2554"
  }
  

• Query Task

  Request:
  POST /query
  {
  	"id":"35adbde5-77c4-4d65-adac-0082d91f2554"
  }
  Response:
  {
      "id": "cb9aefdd-5bd1-4bf3-8c94-1ed5c2ea638e",
      "topic": "order",
      "execute_time": 1504934230,
      "max_retry": 1,
      "has_retry": 0,
      "callback": "http://127.0.0.1:8888/success",
      "content": "hello",
      "creat_time": 1504934220
  }
  

Backend API

• Callback

  Request:
  POST /?
  {
    "id": "57e177ff-454c-42d6-93ab-65895b950dbf",
    "topic": "order",
    "content": "hello"
  }
  Response:
  {
      "code":100 // 100: success,101: too many request,other: fail
  }
  

  At-lease-once delivery, may repeat delivery. Backend api should idempotent and always return response.

Inside Later

Later has four storage part

• Task Pool: kv pairs hold fully task data
• Delay Bucket: a sorted set store task id and execute time, which waiting to execute by worker
• Unack Bucket: a sorted set store task which has called backend server and waiting response
• Error Bucket: a sorted set store task which call backend server fail

Three worker fetch tasks with time ticker

• Delay Worker: get tasks which reach execute time and move tasks from delay bucket to unack bucket, if call backend server success, delete all task data. Otherwise, move tasks from delay bucket to error bucket
• Unack Worker: move tasks from unack bucket to delay bucket
• Error Worker: move tasks from error bucket to delay bucket

Concurrence problem

In general, we will deploy multi instance, workers will get same task, but we judge result when move task from delay bucket to unack bucket, if ZADD return 1, worker move on, otherwise worker return immediately.