Server or CDN region is close to target audience

Network latency is bounded by the speed of light — a request from a user in São Paulo to a server in Singapore must traverse approximately 18,000km of fibre, which takes at minimum 120ms at the speed of light in glass, often 200–400ms in practice when routing overhead is included. ISO-25010 time-behaviour cannot be met for geographically mismatched deployments without a CDN, and for hosting platforms that don't include built-in CDN (Fly.io single region, Railway, bare VPS), the chosen region directly determines TTFB for non-local users. A US-focused marketing site deployed to ap-southeast-1 will consistently fail the 800ms TTFB threshold for US visitors, regardless of how well the application itself is optimised.

For Fly.io, update primary_region in fly.toml to the region closest to your target audience, or add replica regions for multi-geography coverage.

# fly.toml
[build]
# US East Coast — optimal for US-focused audiences
primary_region = "iad"

# Add replicas for global audiences:
# fly scale count 2 --region iad,lhr
# iad = Washington DC, lhr = London, nrt = Tokyo, syd = Sydney

For Railway and Render: select the region nearest your primary user base in the deployment settings. For the highest ROI, migrate to Vercel or Netlify — their global CDNs eliminate region selection entirely by serving from the nearest edge node to each visitor automatically.