How to run this repo

sh start.sh

This shell will do the followings

1. running test for routing_api
2. build application_api
3. build routing_api
4. start all the services (consul / application_api / routing_api)
5. inject the app instances into consul by curl

Once the script finished, you can see the 5 services are all up

---

Structure of this repo

1. Files 2. config.env: environment variables 3. docker-compose.yml: define all the services 4. start.sh: start this repo
2. Directory 3. application_api: a backend service which response what you send to it in JSON 4. routing_api: the service which has the capability to distribute the requests to upstream services by round-robin
3. Services
   • Consul: Serve as a service-discovery service, and it can inject the service instances into routing_api
   • 
   • application_api
     • URL
       • application_api_0 => http://localhost:10001/
       • application_api_1 => http://localhost:10002/
       • application_api_2 => http://localhost:10003/
     • API
       • send request:
         • purpose: just send any json payload and get the response with the same payload
         • endpoint = "/"
         • payload: any json
         • method: POST
       • update status:
         • purpose: change the status of this backend service, _0 = health, 1 = slow down, 2 = unavailable
         • endpoint = "/update_status"
         • method: POST
   • routing_api
     • URL: http://localhost:20001
     • API
       • send request:
       • purpose: just send any json payload and get the response with the same payload
       • endpoint = "/", payload: any json
       • response

{
    "1_status": "success",
    "2_data_from_upstream": {
        "game": "Mobile Legends",
        "gamerID": "sid",
        "points": 20
    },
    "3_upstream": {
        "upstream_index": 2,
        "upstream_service": "http://application_api_2:5000"
    },
    "4_response_time_ms_statistic": {
        "current": "3,6,6",
        "previous": "3,6,3"
    },
    "5_resting_number": {
        "current": "0,0,0",
        "previous": "0,0,0"
    },
    "6_explanation": "service 2 is chosen because its resting number is zero",
    "7_rules": "Rules: 1. rest number == 0 | 2.smallest resp time if resp time < timeout",
    "8_metadata": {
        "slow_down_threshold_ms": 100,
        "timeout_threshold_ms": 5000
    }
}

---

Round-Robin

I use 3 kind of information below to implement round-robin. All the RR related logic are under class RoundRobin inside routing_api/util.py. For the core RR logic, please refer to the function get_instance_index, and I put more explanation there.

1. resp_time_stat: list[int] = []
   • record the latest response time (ms) for each service. For ex: [1,10,11] means the response time are 1,10,11 ms individually of service 0,1,2
2. resting_number: list[int] = []
   • record the resting number for each service. if the resting number > 0, means that a service should be skipped after ${resting number} API calls. for ex: [1,2] means servie 0 has to be skipped 1 time.
3. cur_idx = 0
   • means what is the current upstream service we should use.

---

Questions

1. How would my round-robin API handle it if one of the application APIs goes down?
   • If there is an application going down, in my code, I'll give this application a resting number (defined as TIMEOUT_REST_NUMBER in config.env)
   • Before the resting number is decreased to zero, this service should be skipped.
2. How would my round-robin API handle it if one of the application APIs starts to go slowly?
   • If there is an application slow down, in my code, I'll give this application a resting number (defined as SLOW_DOWN_REST_NUMBER in config.env)
   • Before the resting number is decreased to zero, this service should be skipped.
3. How would I test this application?
   • Assumption: we have 3 instances 0, 1, 2
   • Unit test: routing_api/tests/test_routing_api.py
     • Positive test case: test_positive_no_delay_and_no_timeout
     • Negative test cases:
       • test_negative_one_delay (slow down)
       • test_negative_one_timeout (go down)
       • test_negative_one_timeout_and_one_delay (slow down and go down)
       • test_all_timeout (all go down)
   • Manually test: By [POSTMAN collection], and please refer to the mail
     • Positive test case: test_positive_no_delay_and_no_timeout
     • Negative test cases:
       • test_negative_1_delay (slow down)
       • test_negative_2_delay (slow down)
       • test_negative_3_delay (slow down)
       • test_negative_1_timeout (go down)
       • test_negative_2_timeout (go down)
       • test_negative_3_timeout (go down)
       • test_negative_1_timeout_and_1_delay (slow down and go down)
       • test_negative_2_timeout_and_1_delay (slow down and go down)
       • test_negative_1_timeout_and_2_delay (slow down and go down)
       • test_all_timeout (all go down)
       • test_all_delay (all slow down)