Alarm Digest Service

Nikolaos Christidis (nick.christidis@yahoo.com) :: Used --> go 1.17rc2

Description - Technical decisions

The core logic of the alarm service is separated in the following 'components':

• Producers - which produce message to nats topic (in our case the AlarmDigest topic where we send the alarms of the user after a 'flush' from a SendAlarmDigest message).

• Listeners - which listen for messages from nats topics (in our case AlarmStatusChanged and SendAlarmDigest topics) and propagate them to consumers through go channels for further processing.

• Consumers - listen for messages on go channels (which got emitted from listeners (from nats topics)), calculate the distribution worker id in order to propagate the message to worker's channel for processing from worker so to distribute the load and scale. In our case the distribution worker id is calculated: workerId <= hash32(userId) % totalNumberOfWorkers. totalNumberOfWorkers are the goroutines which run the worker code-logic. So we can say that consumers are light processors and act as routers based on the message's user id

• Workers - listen for messages to process on its own go channel, messages there are processed based on their type

  • AlarmStatusChanged message --> updates the state of the worker
  • SendAlarmDigest message --> if any critical alarms for the user it will send to a dedicated go channel which eventually will be picked from Producers and emit these to AlarmDigest topic.

• Some notes:

  • The approach for all components was share-nothing approach, and all go routines communicate with channels. No mutexes-locks have been used (in order to avoid bottlenecks and scale, etc.) Moreover, Go does not have sophisticated concurrent datastructures (eg: CompareAndSet) out of the box, so channels is definitely the way to go in terms of concurrency - work splitting.

  • Worker component has its own local-state (maps, etc.), so it is somehow an actor which a go channel plays the role of its mailbox, and listens there for incoming tasks.

• Diagram:

Improvements

Persistence

As stated in the exercise messages should always be delivered and not lost. NATS is a fire and forget infra (Core NATS is a fire-and-forget messaging system, will only hold messages in memory and will never write messages directly to disk.), meaning that is not backed-up from persistence, so to store messages and when the consumer-listener is up to pull/push.

Moreover, if the alarm-service goes down (eg: due to panic) during send of AlarmDigest, these alarms will be lost, because alarm-service is stateless.

So for this reason, when we consume from NATS we should store to a persistent storage (in our case Cassandra seems a very good fit - write intensive db due to LSM tree). Eg: a good designed table key could be like key(partitionKey(userId, alarmId, status) - clustering key(updatedAt order by desc))

So when we consume we store, worker processes the message, and during flush with SendAlarmDigest, cleans the necessary database records for housekeeping stuff.

How to run (needs to run nats-server first - check related section)

• First: cd alarm/
• Then: go run . OR (go build . and ./alarm)

How to run tests (needs to run nats-server first - check related section)

• First: cd alarm/
• Then: go test ./...
• You should see the following:

chriniko13@chriniko13:~/GolandProjects/netdata_christidis_nick/alarm$ go test ./...
warning: GOPATH set to GOROOT (/home/chriniko13/sdk/go1.17rc2) has no effect
ok      alarm   0.755s
?       alarm/domain    [no test files]
?       alarm/error     [no test files]
?       alarm/fileutil  [no test files]
ok      alarm/hashing   0.001s
ok      alarm/message   0.002s

How to run benchmark

• Execute: cd alarm/ and go test -run=BenchmarkTest -bench=. You should see the following output:

  goos: linux
  goarch: amd64
  WARN[0004] [SendAlarmDigest#Delegator] bad formatted message received from topic: SendAlarmDigest, data: {"UserID":"65396a05-ff57-11eb-a37e-d8bbc1068e57"}
  pkg: alarm
  cpu: AMD Ryzen 5 5600X 6-Core Processor             
  BenchmarkTestBootstrapAlarmService_1-12         INFO[0004] [alarmMessagesWorker#14] WORKER RECEIVED AlarmStatusChangedMessages message: {653e1290-ff57-11eb-a384-d8bbc1068e57 653e1292-ff57-11eb-a384-d8bbc1068e57 CRITICAL 2021-08-17 15:33:59 +0300 EEST}
  WARN[0004] [AlarmStatusChanged#Delegator] bad formatted message received from topic: AlarmStatusChanged, data: {"AlarmID":"653e11d3-ff57-11eb-a383-d8bbc1068e57","ChangedAt":"2021-08-17T15:33:59+03:00","Status":"CRITICAL","UserID":"653e11d4-ff57-11eb-a383-d8bbc1068e57"}
  INFO[0004] [sendAlarmDigestTopicListener#9] message received from topic: SendAlarmDigest.9, data: {65372b78-ff57-11eb-a37e-d8bbc1068e57}
  1        4587239464 ns/op
  INFO[0004] [sendAlarmDigestConsumer#11] SendAlarmDigestMessage received: {65372b78-ff57-11eb-a37e-d8bbc1068e57}
  WARN[0004] disconnected from the server id:  --- error: <nil>
  PASS
  
  

Installing Log

go get "github.com/Sirupsen/logrus"

Installing UUID library

go get github.com/google/uuid

Installing nats libraries

# Go client
go get github.com/nats-io/nats.go/

# Server
go get github.com/nats-io/nats-server

Setting up provided nats-server and verification tool

• nats server and verification tool

docker run -p 4222:4222 --rm -it \
--name be-challenge \
docker.io/lvrach/be-challenge:latest

• then run service

• then execute the verification tool as following

docker exec -it be-challenge verify

• so the output if all okay should be the following

chriniko13@chriniko13:~/GolandProjects/netdata_christidis_nick$ docker exec -it be-challenge verify
2021/08/16 22:38:20 waiting to consume "AlarmDigest" messages
2021/08/16 22:38:20 Smoke test passed