Key-Value Store in NATS: Simple State Management

Example in Go

Create a KV Bucket

js, _ := nc.JetStream()
kv, _ := js.CreateKeyValue(&nats.KeyValueConfig{
    Bucket: "CONFIGS",
})

Put a Value

kv.Put("featureX.enabled", []byte("true"))

Get a Value

entry, _ := kv.Get("featureX.enabled")
fmt.Printf("Value: %s\n", string(entry.Value()))

Watch for Changes

watch, _ := kv.Watch("featureX.*")
for update := range watch.Updates() {
    if update != nil {
        fmt.Printf("Key %s changed to %s\n", update.Key(), string(update.Value()))
    }
}

With Watch, any time a key is updated, subscribers get notified instantly.

Use Case Examples

1. Feature Flags
   • Key: featureX.enabled → Value: true/false.
   • All services watch this key and automatically switch behavior when it changes.
2. Service Discovery (Lightweight)
   • Key: service.auth.url → Value: http://10.0.0.5:8080.
   • Clients always read the latest location of a service.
3. Leader Election
   • Services write a key like leader=node1.
   • Others watch the key to know who the leader is.

Final Thoughts

The NATS KV store is not meant to replace a full database, but it’s perfect for lightweight state, configuration, and coordination. Because it’s built on top of JetStream, it’s reliable and supports history of changes.