This post covers Working with Edge KV Storage — a foundational pattern for stateful edge applications.
How It Works
Store and retrieve key-value data at the edge. Perfect for config, feature flags, and session data distributed globally.
Edge KV storage is eventually consistent. Writes are propagated asynchronously across the global edge network. This means a write in London might take a few hundred milliseconds to be readable in Sydney — but local reads (from the same PoP) are immediate.
Implementation
use fastedge::{
body::Body,
http::{Request, Response, StatusCode, Error},
kv_store::{KvStore, StoreType},
};
#[fastedge::http]
fn main(req: Request<Body>) -> Result<Response<Body>, Error> {
// Open the default KV store
let store = KvStore::open(StoreType::Default)?;
// Read a value
let counter: u64 = store
.get("page_views")
.and_then(|v| v.parse().ok())
.unwrap_or(0);
// Increment and write back
let new_count = counter + 1;
store.put(
"page_views",
&new_count.to_string()
)?;
let body = format!(
"Page views: {}",
new_count
);
Response::builder()
.status(StatusCode::OK)
.header("content-type", "text/plain")
.body(Body::from(body))
} Use Cases
- Feature flags — enable/disable features globally without redeploying your worker
- Session state — persist data across requests without a central database
- Rate limiting — aggregate request counters across the edge network
- Configuration — store per-tenant settings that update without code changes
- Cache — store computed results close to users for sub-millisecond retrieval
Consistency Model
Edge KV is eventually consistent with read-your-writes semantics at the local PoP. If you write a value, subsequent reads from the same edge location will see the update immediately. Reads from other locations may briefly see the old value until the write propagates (typically 100-500ms).
Tip: For strongly consistent writes, write through to your origin database and use edge KV as a read cache. This gives you the best of both worlds: strong consistency at write time and edge-speed reads.
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