How to Simulate Bandwidth Constraints Using lueur

his guide shows you how to reduce or throttle network bandwidth in your application flow with lueur. You’ll see examples of slowing traffic on the server side, client side, or both directions.

Prerequisites

• Install lueur

  If you haven’t installed Lueur yet, follow the installation instructions.

• Basic Proxy Setup Be familiar with running lueur run --with-[fault] commands from your terminal.

Severe Upstream Slowdown

In this scenario, server-side ingress traffic is heavily constrained, so data returning from the server becomes painfully slow for the client.

Any responses from the server are throttled to 500 kbps, causing slow downloads or streaming on the client side.

• Start the proxy with bandwidth set from server-side ingress

  lueur run \
      --with-bandwidth \ # (1)!
      --bandwidth-side server \ # (2)!
      --bandwidth-direction ingress \ # (3)!
      --bandwidth-rate 500 \ # (4)!
      --bandwidth-unit kbps
  

  1. Enable the bandwidth fault support
  2. Apply the fault on server side
  3. Apply the fault on ingress
  4. Set a very limited bandwidth to 500kbps

Light Client Slowdown

Here, you cap both inbound and outbound bandwidth on the client side, but only to a moderate level.

The client’s uploads and downloads are each capped at 1 Mbps. This tests how your app behaves if the client is the bottleneck.

• Start the proxy with bandwidth set from client-side both ingress and egress

  lueur run \
      --with-bandwidth \ # (1)!
      --bandwidth-side client \ # (2)!
      --bandwidth-direction both \ # (3)!
      --bandwidth-rate 1 \ # (4)!
      --bandwidth-unit mbps
  

  1. Enable the bandwidth fault support
  2. Apply the fault on client side
  3. Apply the fault on ingress and egress
  4. Set a reduced bandwidth to 1mbps

Throughput Degradation

In this scenario, we combine ingress and egress on the server side, giving a moderate throughput limit of 2 Mbps. This is helpful for general "server is maxing out" scenarios.

Uploads and downloads from the server are capped at 2 Mbps, simulating moderate network constraints on the server side.

• Start the proxy with bandwidth set from server-side both ingress and egress

  lueur run \
      --with-bandwidth \ # (1)!
      --bandwidth-side server \ # (2)!
      --bandwidth-direction both \ # (3)!
      --bandwidth-rate 2 \ # (4)!
      --bandwidth-unit mbps
  

  1. Enable the bandwidth fault support
  2. Apply the fault on server side
  3. Apply the fault on ingress and egress
  4. Set a reduced bandwidth to 2mbps

Mobile Edge / 3G‐Style Network

Simulates a high‐latency, low‐throughput link.

The user sees slow and sluggish performance typical of older mobile networks.

• Start the proxy with bandwidth and latency faults

  lueur run \
      --duration 10m \
      --with-bandwidth \  # (1)!
          --bandwidth-side client \
          --bandwidth-direction both \
          --bandwidth-rate 384 \
          --bandwidth-unit kbps \
      --with-latency \  # (2)!
          --latency-mean 200 \
          --latency-stddev 50
  

  1. Both ingress and egress are capped to about 384 kbps (typical of older 3G)
  2. Latency of ~200±50ms is layered on to reflect mobile edge behavior

Next Steps

• Combine with Latency: For a more realistic environment, layer static latency (--with-latency) plus bandwidth fault.