mini-redis
mini-redis is an incomplete, idiomatic implementation of a
Redis client and server built with
Tokio.
The intent of this project is to provide a larger example of writing a Tokio
application.
Disclaimer Please don't use mini-redis in production. This project is
intended to be a learning resource, and omits various parts of the Redis
protocol because implementing them would not introduce any new concepts. We will
not add new features because you need them in your project — use one of the
fully featured alternatives instead.
Why Redis
The primary goal of this project is teaching Tokio. Doing this requires a
project with a wide range of features with a focus on implementation simplicity.
Redis, an in-memory database, provides a wide range of features and uses a
simple wire protocol. The wide range of features allows demonstrating many Tokio
patterns in a "real world" context.
The Redis wire protocol documentation can be found here.
The set of commands Redis provides can be found
here.
Running
The repository provides a server, client library, and some client executables
for interacting with the server.
Start the server:
RUST_LOG=debug cargo run --bin mini-redis-server
The tracing crate is used to provide structured logs.
You can substitute debug with the desired log level.
Then, in a different terminal window, the various client examples
can be executed. For example:
cargo run --example hello_world
Additionally, a CLI client is provided to run arbitrary commands from the
terminal. With the server running, the following works:
cargo run --bin mini-redis-cli set foo bar
cargo run --bin mini-redis-cli get foo
OpenTelemetry
If you are running many instances of your application (which is usually the case
when you are developing a cloud service, for example), you need a way to get all
of your trace data out of your host and into a centralized place. There are many
options here, such as Prometheus, Jaeger, DataDog, Honeycomb, AWS X-Ray etc.
We leverage OpenTelemetry, because it's an open standard that allows for a
single data format to be used for all the options mentioned above (and more).
This eliminates the risk of vendor lock-in, since you can switch between
providers if needed.
AWS X-Ray example
To enable sending traces to X-Ray, use the otel feature:
RUST_LOG=debug cargo run --bin mini-redis-server --features otel
This will switch tracing to use tracing-opentelemetry. You will need to
have a copy of AWSOtelCollector running on the same host.
For demo purposes, you can follow the setup documented at
https://github.com/aws-observability/aws-otel-collector/blob/main/docs/developers/docker-demo.md#run-a-single-aws-otel-collector-instance-in-docker
Supported commands
mini-redis currently supports the following commands.
The Redis wire protocol specification can be found
here.
There is no support for persistence yet.
Tokio patterns
The project demonstrates a number of useful patterns, including:
TCP server
server.rs starts a TCP server that accepts connections,
and spawns a new task per connection. It gracefully handles accept errors.
Client library
client.rs shows how to model an asynchronous client. The
various capabilities are exposed as async methods.
State shared across sockets
The server maintains a Db instance that is accessible from all connected
connections. The Db instance manages the key-value state as well as pub/sub
capabilities.
Framing
connection.rs and frame.rs show how to
idiomatically implement a wire protocol. The protocol is modeled using an
intermediate representation, the Frame structure. Connection takes a
TcpStream and exposes an API that sends and receives Frame values.
Graceful shutdown
The server implements graceful shutdown. tokio::signal is used to listen for
a SIGINT. Once the signal is received, shutdown begins. The server stops
accepting new connections. Existing connections are notified to shutdown
gracefully. In-flight work is completed, and the connection is closed.
Concurrent connection limiting
The server uses a Semaphore limits the maximum number of concurrent
connections. Once the limit is reached, the server stops accepting new
connections until an existing one terminates.
Pub/Sub
The server implements non-trivial pub/sub capability. The client may subscribe
to multiple channels and update its subscription at any time. The server
implements this using one broadcast channel per channel and a
StreamMap per connection. Clients are able to send subscription commands to
the server to update the active subscriptions.
Using a std::sync::Mutex in an async application
The server uses a std::sync::Mutex and not a Tokio mutex to synchronize
access to shared state. See db.rs for more details.
Testing asynchronous code that relies on time
In tests/server.rs, there are tests for key expiration.
These tests depend on time passing. In order to make the tests deterministic,
time is mocked out using Tokio's testing utilities.
Contributing
Contributions to mini-redis are welcome. Keep in mind, the goal of the project
is not to reach feature parity with real Redis, but to demonstrate
asynchronous Rust patterns with Tokio.
Commands or other features should only be added if doing so is useful to
demonstrate a new pattern.
Contributions should come with extensive comments targeted to new Tokio users.
Contributions that only focus on clarifying and improving comments are very
welcome.
License
This project is licensed under the MIT license.
Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in mini-redis by you, shall be licensed as MIT, without any
additional terms or conditions.