go-redisp is a Redis proxy service. This proxy implements a subset of the Redis protocol, with the ability to add additional features on top of Redis (e.g. caching and sharding).

Runtime

Build go-redisp by execute the following command

$ go build

Launch the backing Redis by issuing this command

$ redis-server --daemonize yes

Launch Redis Proxy by issuing this command

$ go-redisp

This will start the web server listening on port 9997 (configurable using the conf.yaml file).

Once the server is up and running, send a curl http://localhost:9997/get?key=abc command to fetch for a stored value. If a value is not found, a 404 will return to the client.

Launch Redis with Docker

go-redisp is configured with a Dockerfile and docker-compose.yml where you may build a Docker image and launch the service in a swamp.

To build the Docker image,

$ go build

$ docker build -t go-redisp .

To run with Docker,

docker run -p 9997:9997 -ti -v /tmp:tmp go-redisp /bin/bash

High-level architecture

go-redisp will be implemented as a REST API service. At the start, there will be a single endpoint '/get?key=xyz'.

As for Redis client, I chose github.com/go-redis/redis for its simplicity.

In order to enforce a single client only, I will use a Mutex lock from the entry. Only one client may obtain the lock at a time.

For LRU eviction, instead of using a sorted map (by int), I opted for using a regular map and will perform a sort when I need to drop an entry. I am assuming the turn over is small hence I trade it for not sorting the map upon every get.

Requirements

Single backing instance

Each instance of the proxy service is associated with a single Redis service instance called the “backing Redis” .

Cached GET

A GET command, directed at the proxy, returns the value of the specified key from the proxy’s local cache if the local cache contains a value for that key. If the local cache does not contain a value for the specified key, it fetches the value from the backing Redis instance and stores it in the local cache, associated with the specified key.

Global expiry

Entries added to the proxy cache are expired after being in the cache for a time duration that is globally configured per instance . After an entry is expired, a GET command will act as if the value associated with the key was never stored in the cache.

LRU eviction

One the cache fills to capacity, the least recently used key is evicted each time a new key needs to be added to the cache.

Fixed key size

The cache capacity is configured in terms of number of keys it retains.

Single client

The proxy is able to process at least one concurrent client request i.e. when more than one client makes a request to the proxy at the same time, the second client’s request only starts processing once the first one has completed .

Configuration