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How to Simulate HTTP Errors Using fault

This guide will walk you through emulating application level HTTP errors into your application using fault proxy capabilities.

Prerequisites

  • Install fault

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

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

Warning

Currently HTTP errors can only be applied against HTTP proxy forwarding traffic. It doesn't work yet with tunneling traffic. The reason is that, when fault use the tunneling approach the network streams are opaque to fault. Therefore it cannot figure the protocol going though. One could write a plugin to achieve this but it's not a core feature yet.

This HTTP error work against forward proxying but not tunneling proxy nor raw TCP proxies.

Constant Internal Server Error

  • Start the proxy with HTTP Error 500 from the remote server

    fault run \
    --with-http-response \ # (1)!
    --http-response-status 500 \ # (2)!
    --http-response-trigger-probability 1  # (3)!
    1. Enable the HTTP error fault support
    2. Set the status to 500
    3. Set the error on all responses

Intermittent Service Unavailable Errors

  • Start the proxy with HTTP Error 503 from the remote server

    fault run \
    --with-http-response \ # (1)!
    --http-response-status 503 \ # (2)!
    --http-response-trigger-probability 0.5  # (3)!
    1. Enable the HTTP error fault support
    2. Set the status to 503
    3. Set the error on half of the responses

Intermittent Not Found Errors

  • Start the proxy with HTTP Error 404 from the remote server

    fault \
    --with-http-response \ # (1)!
    --http-response-status 404 \ # (2)!
    --http-response-trigger-probability 0.5 \ # (3)!
    --http-response-body '{"error": "true"}' # (4)!
    1. Enable the HTTP error fault support
    2. Set the status to 404
    3. Set the error on half of the responses
    4. Set a JSON response body