View Source erlmld
This application allows Kinesis and DynamoDB streams to be processed using Erlang (by way of the KCL MultiLangDaemon).
Erlang - MultiLangDaemon concept
The Kinesis Client Library abstracts away the distribution of work among a group of workers which are processing data found on a Kinesis stream, including lease management and the assignment of specific workers to specific shards.
A component of the KCL is the MultiLangDaemon, which allows non-Java applications to be more easily integrated with the KCL by way of a simple JSON protocol: it launches one subprocess per owned shard and communicates on stdin/stdout.
AdRoll needed the ability to perform Kinesis data processing in an Erlang system, and thus
this project was born. We launch one
erlmld supervision tree per Kinesis/DynamoDB
stream being processed in an Erlang node. This results in an instance of the
MultiLangDaemon being launched as a port program for each stream being processed.
Each MLD process in turn launches one subprocess for each owned shard; these are simply netcat or socat processes which map I/O back to the Erlang node via TCP, allowing us to do all data processing in Erlang:
gen_statem worker implements the MLD protocol on the Erlang side; one of these runs in
a process for each shard owned by the current worker.
A MultiLangDaemon adapter supports DynamoDB streams using the same MLD protocol.
AdRoll uses this to implement a high-performance global cache population system which supports a real-time bidding platform also implemented in Erlang.