Kinesumer

Kinesumer is a Go client implementing a client-side distributed consumer group client for Amazon Kinesis. It supports following features:

• Implement the client-side distributed Kinesis consumer group client.
• A client can consume messages from multiple Kinesis streams.
• Clients are automatically assigned a shard id range for each stream.
• Rebalance each shard id range when clients or upstream shards are changed. (by restart or scaling issues)
• Manage the checkpoint for each shard, so that clients can continue to consume from the last checkpoints.
• Able to consume from the Kinesis stream in a different AWS account.
• Manage all the consumer group client states with a DynamoDB table. (we call this table as state store.)

Setup

Kinesumer manages the state of the distributed clients with a database, called "state store". It uses the DynamoDB as the state store, so you need to create a DynamoDB table first. Create a table with LSI schema. See the details in here.

Current state store implementation supports multiple applications (you will pass the app name when initialize the client). So, if you already have a kinesumer state store, you don't need to create another state store table.

If your Kinesis stream is in different account

If you want to connect to Kinesis in a different account, you need to set up the IAM role to access to the target account, and pass the role arn (kinesumer.Config.RoleARN) when initialze the Kinesumer client: Reference.

Usage

package main

import (
    "fmt"
    "time"

    "github.com/daangn/kinesumer"
)

func main() {
    client, err := kinesumer.NewKinesumer(
        &kinesumer.Config{
            App:            "myapp",
            KinesisRegion:  "ap-northeast-2",
            DynamoDBRegion: "ap-northeast-2",
            DynamoDBTable:  "kinesumer-state-store",
            ScanLimit:      1500,
            ScanTimeout:    2 * time.Second,
        },
    )
    if err != nil {
        // Error handling.
    }

    go func() {
        for err := range client.Errors() {
            // Error handling.
        }
    }()

    // Consume multiple streams.
    // You can refresh the streams with `client.Refresh()` method.
    records, err := client.Consume([]string{"stream1", "stream2"})
    if err != nil {
        // Error handling.
    }

    for record := range records {
        fmt.Printf("record: %v\n", record)
    }
}

How it works

Kinesumer implements the client-side distributed consumer group client without any communications between clients. Then, how do clients know the state of an entire system? The answer is the distributed key-value store.

To evenly distribute the shard range among clients, the Kinesumer relies on a centralized database, called state store. State store manages the states of the distributed clients, shard cache, and checkpoints.

This is the overview architecture of Kinesumer:

Following explains how the Kinesumer works:

• Leader election: Clients register themselves to the state store and set their indexes. The index is determined by sorting all active client ids. And, a client who has zero index will be a leader. So, when clients are scaled or restarted, the leader could be changed.
• Shard rebalancing: A client will fetch the full shard id list and client list from the state store. Then, divide the shard id list by the number of clients and assign a range of shard id corresponding to their index. All clients will repeat this process periodically.
• Synchronization: The leader client is responsible to sync the shard cache with the latest shard list, and pruning the outdated client list (to prevent the orphan shard range) periodically.
• Offset checkpoint: Whenever a client consumes messages from its assigned shards, it updates a per-shard checkpoint with the sequence number of the last message read from each shard.

License

See LICENSE.