The test consist in building a small distributed online-counter.

It is split in 3 components:

• A "client"
• A "gateway"
• A "status" service

You need to build and package all three components.

To keep things simple, all the schemas are in a single protobuf file, but you're free to split it if you want.

You need to write a gRPC client that:

• has a unique identifier
• connects to the gateway
• the gateway is going to send a Ping every 1s to the client.
• the client must respond with a Pong, containing a Status (cf protos/service.proto)

You're free to write the client either in Go or Rust

You need to write a gRPC server that:

• allows multiple simultaneous clients to connect with persistent connections
• ping each connected client at a specific clockrate (a client must receive a Ping every 1s)
• the gateway must notify the status service
  • You're free to choose how the gateway talks to the status service (gRPC, event, ...)
• must be horizontally scalable
• Write a Dockerfile, as much production-ready as you can
• If any, point out scalability issues of your system / how you would fix them

You're free to write the gateway either in Go or Rust

You need to write a microservice that:

• can react to messages sent by the gateway
  • You're free to choose how the gateway talks to the status service (gRPC, event, ...)
• must expose a StatusReader gRPC service
• the service keeps track of how many unique users were online in the last 3mins
  • a user is considered online if they reported a STATUS_EVEN or STATUS_ODD status.
• must be resilient to reboots
  • you're free to use any kind of database you want
• must be horizontally scalable
• Write a Dockerfile, as much production-ready as you can
• If any, point out scalability issues of your system / how you would fix them

You must write this service in Go

Finally, write a docker-compose to run all the services and allow for easy testing.

• Write tests
• Add tracing instrumentation
• Build everything with Bazel:
  • Executables
  • Mutliplatform docker images

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