Simulate Poor Network Conditions

This guide explains how to use the staged toxic proxy setup to simulate poor network conditions when developing Open Data Capture.

When you run scripts/toxic-proxy.sh, it configures Toxiproxy with the following simulated network conditions:

• Downstream bandwidth limit (API → browser): capped at 5,000 KB/second (~5 MB/s).
• Upstream bandwidth limit (browser → API): capped at 2,500 KB/second (~2.5 MB/s).
• Intermittent latency and jitter (downstream):
  • Base latency of 50 ms, plus up to 500 ms of jitter.
  • Applied with 20% toxicity, meaning only about 1 in 5 downstream requests/responses are delayed in this way.
• Occasional random connection resets (downstream):
  • Connections are randomly reset/closed from the proxy side.
  • Applied with 10% toxicity, so roughly 1 in 10 downstream connections will be abruptly terminated.

Together, these toxics approximate a slow, unstable network where responses arrive slowly, some requests suffer extra delay, and a minority of connections fail unexpectedly.

Prerequisites

• Install Toxiproxy (both toxiproxy-server and toxiproxy-cli) and ensure they are available on your PATH.

Steps

1. Set the toxic proxy port in .env

   Choose a port for the toxic proxy (for example 5501) and set:

   • API_DEV_TOXIC_PROXY_PORT=5501

2. Point the frontend at the toxic proxy

   Update API_BASE_URL to use the same port on localhost:

   • API_BASE_URL=http://localhost:5501

3. Start the toxic proxy

   Run:

   scripts/toxic-proxy.sh

   Leave this running. It creates a proxy that sits between the frontend and the API server and applies bandwidth limits.

4. Launch the app as normal

   In another terminal, run:

   pnpm dev

Notes

• The proxy reads API_DEV_SERVER_PORT from .env to know where your API server is listening.
• If API_DEV_TOXIC_PROXY_PORT is empty, the script exits without starting the proxy.