Fix Kubernetes Pod Crash with Flutter Backend

Kubernetes Pod Crashes Serving Flutter Apps

While Flutter is primarily a client-side framework, it's common to containerize Flutter web builds behind an Nginx server or run Dart backends with dart_frog or shelf. When these pods crash, here's how to fix them.

Flutter Web + Nginx: 403 Forbidden

The build output must be copied to the right Nginx directory:

# Build stage
FROM ghcr.io/cirruslabs/flutter:stable AS build
WORKDIR /app
COPY . .
RUN flutter build web --release

# Serve stage
FROM nginx:alpine
COPY --from=build /app/build/web /usr/share/nginx/html
COPY nginx.conf /etc/nginx/conf.d/default.conf
EXPOSE 80

Make sure nginx.conf handles SPA routing:

server {
  listen 80;
  root /usr/share/nginx/html;
  index index.html;

  location / {
    try_files $uri $uri/ /index.html;
  }
}

Dart Backend Crashes

For Dart server applications, common pod crash causes include:

// Binding to localhost won't work in K8s
// Wrong:
final server = await shelf_io.serve(handler, 'localhost', 8080);

// Right:
final server = await shelf_io.serve(handler, '0.0.0.0', 8080);

Health Checks

Add a health endpoint to prevent liveness probe failures:

Router()
  ..get('/healthz', (Request req) => Response.ok('ok'))
  ..get('/api/data', handleData);

Bugsly's lightweight Dart integration captures unhandled exceptions from your server process, so crashed pods leave a clear error trail for post-mortem debugging.