# How Openship CDN Edge Caching Works with Brotli Compression

> Learn how Openship CDN edge caching optimizes asset delivery with Brotli compression and intelligent fallback for faster website performance globally.

- Repository: [oblien/openship](https://github.com/oblien/openship)
- Tags: deep-dive
- Published: 2026-07-23

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**Openship's self-hosted CDN automatically serves Brotli-compressed static assets from globally distributed edge nodes, falling back to uncompressed or gzip payloads when clients lack Brotli support.**

The oblien/openship repository implements a globally distributed edge network that accelerates static asset delivery through intelligent caching and modern compression algorithms. When a request reaches an Openship edge node, the system inspects client capabilities and serves Brotli-encoded content whenever possible, reducing transfer sizes by 20–30% compared to gzip. Understanding how Openship CDN edge caching integrates with Brotli compression reveals the architecture that enables low-latency responses across global deployments.

## Edge Node Request Flow

When a client requests a static asset—such as a page bundle, image, or uploaded file—the edge proxy executes a six-step resolution process defined in the runtime adapters:

1. **Local cache lookup** – The edge node first queries its local cache storage. If a fresh copy exists matching the request signature, it returns the asset immediately without contacting the origin.

2. **Origin fetch on miss** – For cache misses, the edge node forwards the request to the origin server (either the Openship API or the designated storage service). The response is stored in the edge cache for subsequent requests.

3. **Brotli content negotiation** – The edge proxy inspects the `Accept-Encoding` request header. When the client advertises support for `br` (Brotli), the server either serves a pre-compressed variant generated at upload time or dynamically compresses the response before transmission.

4. **Protocol optimization** – All edge nodes speak HTTP/3 (QUIC) out-of-the-box, providing multiplexed streams and reduced handshake overhead for latency-critical clients.

5. **Cache invalidation** – Upon new static bundle deployment, Openship issues a purge request to every edge node (see the implementation in [`apps/dashboard/src/lib/api/projects.ts`](https://github.com/oblien/openship/blob/main/apps/dashboard/src/lib/api/projects.ts)), guaranteeing clients receive the latest version without stale data.

6. **URL resolution** – Assets are referenced via URLs constructed from the `CDN_UPLOAD_URL` environment variable defined in [`apps/api/src/config/env.ts`](https://github.com/oblien/openship/blob/main/apps/api/src/config/env.ts), allowing the frontend to point directly to edge-cached locations.

## Brotli Compression Strategy

Openship handles Brotli encoding through two complementary mechanisms: pre-compressed uploads and dynamic edge compression.

**Pre-compressed uploads** occur when the API layer uploads assets directly to the CDN. In [`apps/api/src/lib/screenshots.ts`](https://github.com/oblien/openship/blob/main/apps/api/src/lib/screenshots.ts), the upload logic sets the `Content-Encoding: br` header to indicate the payload is already Brotli-compressed, allowing the edge node to store the optimized variant without additional CPU overhead.

**Dynamic compression** triggers when a client supports Brotli but requests an asset that exists in the cache only in its uncompressed form. The edge node compresses the response on-the-fly before sending it to the client, balancing CPU usage against bandwidth savings.

If the client does not advertise `br` in the `Accept-Encoding` header, the edge falls back to the uncompressed payload or gzip, depending on configuration.

## Implementation in the Openship Codebase

The CDN integration spans multiple packages, from environment configuration to runtime adapters.

### Uploading Brotli-Compressed Assets

The API layer handles asset uploads in [`apps/api/src/lib/screenshots.ts`](https://github.com/oblien/openship/blob/main/apps/api/src/lib/screenshots.ts). This module checks for the `CDN_UPLOAD_URL` environment variable and uploads screenshots with Brotli encoding hints:

```typescript
// apps/api/src/lib/screenshots.ts
import fetch from "node-fetch";
import { env } from "../config/env";

const cdnUploadUrl = env.CDN_UPLOAD_URL; // Configured via CDN_UPLOAD_URL

export async function uploadScreenshot(buf: Buffer, filename: string) {
  if (!cdnUploadUrl) return null;               // No CDN → fallback to local storage
  const res = await fetch(`${cdnUploadUrl}/${filename}`, {
    method: "PUT",
    headers: {
      "Content-Type": "image/png",
      "Content-Encoding": "br",                 // Hint: upload already Brotli-compressed
    },
    body: buf,
  });
  if (!res.ok) throw new Error(`CDN upload failed: ${res.status}`);
  return `${cdnUploadUrl}/${filename}`;          // Saved CDN URL
}

```

### Runtime Edge Cache Adapter

The runtime adapter in [`packages/adapters/src/runtime/cloud.ts`](https://github.com/oblien/openship/blob/main/packages/adapters/src/runtime/cloud.ts) abstracts the underlying reverse proxy (Nginx, Caddy, or a custom HTTP/3 server) and exposes a unified fetch interface. This adapter automatically handles cache lookup, Brotli compression based on `Accept-Encoding`, and HTTP/3 transport:

```typescript
// packages/adapters/src/runtime/cloud.ts
export async function fetchWithEdgeCache(url: string, init?: RequestInit) {
  // The edge node automatically handles:
  //   • Cache lookup
  //   • Brotli compression based on Accept-Encoding
  //   • HTTP/3 transport
  const response = await fetch(url, {
    ...init,
    headers: {
      ...(init?.headers ?? {}),
      "Accept-Encoding": "br, gzip, deflate, identity", // Ask for Brotli first
    },
  });
  return response;
}

```

### Instant Cache Invalidation

When a new static bundle deploys, the dashboard triggers a purge operation defined in [`apps/dashboard/src/lib/api/projects.ts`](https://github.com/oblien/openship/blob/main/apps/dashboard/src/lib/api/projects.ts). This forces edge nodes to discard stale copies immediately:

```typescript
// apps/dashboard/src/lib/api/projects.ts
import { apiClient } from "./client";

export async function clearCdnCache() {
  // Triggers the edge-nodes to discard stale copies
  await apiClient.post("/admin/purge-cdn");
}

```

## Configuration and Environment Setup

The CDN endpoint URL is injected via the `CDN_UPLOAD_URL` environment variable declared in [`apps/api/src/config/env.ts`](https://github.com/oblien/openship/blob/main/apps/api/src/config/env.ts). When this variable is unset, the system falls back to local storage, ensuring development environments function without external CDN dependencies.

Assets uploaded through the API layer receive persistent CDN URLs stored in the database, allowing frontend components to reference edge-cached locations directly. According to the source in [`apps/api/src/config/env.ts`](https://github.com/oblien/openship/blob/main/apps/api/src/config/env.ts) (line 243), this configuration point controls whether the screenshot utility and other asset handlers route traffic through the distributed edge network or local filesystem storage.

## Summary

- Openship implements a **self-hosted, globally distributed CDN** using runtime adapters that abstract reverse-proxy implementations.
- **Brotli compression** is negotiated via the `Accept-Encoding` header, with support for both pre-compressed uploads and dynamic edge compression.
- Cache invalidation occurs **instantly** across all edge nodes when administrators trigger the purge endpoint after deployments.
- The `CDN_UPLOAD_URL` environment variable controls CDN routing, while [`packages/adapters/src/runtime/cloud.ts`](https://github.com/oblien/openship/blob/main/packages/adapters/src/runtime/cloud.ts) manages the edge-fetch logic.
- All edge nodes support **HTTP/3 (QUIC)** and automatic protocol negotiation for optimal performance.

## Frequently Asked Questions

### Does Openship require a third-party CDN provider?

No. Openship ships with its own self-hosted CDN infrastructure. While you can configure `CDN_UPLOAD_URL` to point to external services, the default runtime adapters in [`packages/adapters/src/runtime/cloud.ts`](https://github.com/oblien/openship/blob/main/packages/adapters/src/runtime/cloud.ts) implement edge caching using your own infrastructure (Nginx, Caddy, or custom HTTP/3 servers), giving you full control over the caching layer.

### How does Openship handle clients that don't support Brotli?

When the `Accept-Encoding` header lacks `br`, the edge node automatically serves the uncompressed asset or a gzip-compressed variant if available. The fetch logic in the cloud adapter requests `br, gzip, deflate, identity` in that order, ensuring graceful degradation without client-side errors.

### What triggers a CDN cache purge in Openship?

Deployments of new static bundles trigger the `clearCdnCache()` function in [`apps/dashboard/src/lib/api/projects.ts`](https://github.com/oblien/openship/blob/main/apps/dashboard/src/lib/api/projects.ts), which sends a POST request to `/admin/purge-cdn`. This operation invalidates cached assets across all edge nodes immediately, ensuring users receive the latest version of JavaScript bundles, images, and other static files.

### Is HTTP/3 supported on all Openship edge nodes?

Yes. According to the runtime adapter implementation, all edge nodes speak HTTP/3 (QUIC) out-of-the-box. The `fetchWithEdgeCache` adapter handles the underlying transport automatically, requiring no additional configuration to enable multiplexed streams and reduced handshake latency for supporting clients.