[![Crates.io][crates-badge]][crates-url]
[![MIT licensed][mit-badge]][mit-url]
## Cluster Mode
Create and manage distributed applications in Rust.
Built with the motto - *Plug the crate in, it'll be taken care of.*
## Usage
```rust
#[tokio::main]
async fn main() {
let result = KubernetesDiscoverService::init("demo".to_string(), "default".to_string())
.await;
if let Ok(k8s) = result {
let cluster = Arc::new(Cluster::default());
let client = DiscoveryClient::new(k8s);
tokio::spawn(start_cluster(cluster, client));
}
}
```
The `Cluster` struct provides a set of functions for example `async fn primaries(&self) -> Option<HashSet<RestClusterNode>>`
or `async fn is_active(&self) -> bool` to communicate with the cluster.
Checkout [doc.rs][doc-cluster-mode-cluster]
## How Cluster Mode works
`cluster-mode` handles three task -
* Discovery
* Consensus
* The Cluster
### Discovery
It uses [rust-cloud-discovery] crate for discovery service. Given a valid implementation of the
crate, cluster-mode should be able to handle the addition of a new node or termination of an
existing or unreachable node.
Check [rust-cloud-discovery] for available implementations.
### Consensus
The main hurdle of a distributed system is consensus. For that, we're using [almost-raft]; the crate
handles leader election only, once enough is discovered by the discovery service.
Note that, `cluster-mode` supports only a single primary, a limitation imposed by `almost-raft`.
Also, it doesn't handle log consistency; it's up to the developer how to maintain consistency.
Hoping to add these features in the future.
### The Cluster
`cluster-mode` initialises the cluster in `Inactive` state. Then works hand to hand with the
discovery service & the consensus algorithm to elect primary and secondaries. The crate tries to
maintain a consistent set of secondaries & secondaries and provide a set of APIs enabling
developers to work with the cluster.
[rust-cloud-discovery]: https://crates.io/crates/rust-cloud-discovery
[doc-cluster-mode]: https://docs.rs/cluster-mode
[doc-cluster-mode-cluster]: https://docs.rs/cluster-mode/latest/cluster-mode/struct.Cluster.html
[almost-raft]: https://crates.io/crates/almost-raft
[crates-badge]: https://img.shields.io/crates/v/cluster-mode.svg
[crates-url]: https://crates.io/crates/cluster-mode
[mit-badge]: https://img.shields.io/badge/license-MIT-blue.svg
[mit-url]: https://github.com/tokio-rs/tokio/blob/master/LICENSE