Proxy for simulating real-world distributed system failures to improve resilience in your applications.

Muxy is a proxy that mucks with your system and application context, operating at Layers 4, 5 and 7, allowing you to simulate common failure scenarios from the perspective of an application under test; such as an API or a web application.

If you are building a distributed system, Muxy can help you test your resilience and fault tolerance patterns.

• Introduction - Contents
• Features
• Installation - On Mac OSX using Homebrew - Using Go Get
• Using Muxy - 5-minute example - Muxy as part of a test suite - Notes
• Proxies and Middlewares - Proxies - HTTP Proxy - TCP Proxy - Middleware - Delay - HTTP Tamperer - Network Shaper - TCP Tamperer - Logger
• Configuration Reference
• Examples - Hystrix
• Usage with Docker
• Extending Muxy - Proxies - Middleware
• Contributing

• Ability to tamper with network devices at the transport level (Layer 4)
• Ability to tamper with the TCP session layer (Layer 5)
• ...and HTTP requests/responses at the HTTP protocol level (Layer 7)
  • Supports custom proxy routing (aka basic reverse proxy)
  • Advanced matching rules allow you to target specific requests
  • Introduce randomness into symptoms
• Simulate real-world network connectivity problems/partitions for mobile devices, distributed systems etc.
• Ideal for use in CI/Test Suites to test resilience across languages/technologies
• Simple native binary installation with no dependencies
• Extensible and modular architecture
• An official Docker container to simplify uses cases such as Docker Compose

Download a release for your platform and put it somewhere on the PATH.

If you are using Homebrew you can follow these steps to install Muxy:

brew install https://raw.githubusercontent.com/mefellows/muxy/master/scripts/muxy.rb

go get github.com/mefellows/muxy

Muxy is typically used in two ways:

1. In local development to see how your application responds under certain conditions
2. In test suites to automate resilience testing

1. Install Muxy

2. Create configuration file config.yml:

   # Configures a proxy to forward/mess with your requests
   # to/from www.onegeek.com.au. This example adds a 5s delay
   # to the response.
   proxy:
     - name: http_proxy
       config:
         host: 0.0.0.0
         port: 8181
         proxy_host: www.onegeek.com.au
         proxy_port: 80
   
   # Proxy plugins
   middleware:
     - name: http_tamperer
       config:
         request:
           host: "www.onegeek.com.au"
   
     # Message Delay request/response plugin
     - name: delay
       config:
         request_delay: 1000
         response_delay: 500
   
     # Log in/out messages
     - name: logger

3. Run Muxy with your config: muxy proxy --config ./config.yml

4. Make a request to www.onegeek.com via the proxy: time curl -v -H"Host: www.onegeek.com.au" http://localhost:8181/. Compare that with a request direct to the website: time curl -v www.onegeek.com.au - it should be approximately 5s faster.

That's it - running Muxy is a matter of configuring one or more Proxies, with 1 or more Middleware components defined in a simple YAML file.

1. Create an application
2. Build in fault tolerence (e.g. using something like Hystrix)
3. Create integration tests
4. Run Muxy configuring a proxy such as HTTP, and one or more symptoms such as network latency, partition or HTTP error
5. Point your app at Muxy
6. Run tests and check if system behaved as expected
7. Profit!

Muxy is a stateful system, and mucks with your low-level (system) networking interfaces and therefore cannot be run in parallel with other tests. It is also recommended to run within a container/virtual machine to avoid unintended consequences (like breaking Internet access from the host).

Simple HTTP(s) Proxy that starts up on a local IP/Hostname and Port.

Example configuration snippet:

proxy:
  - name: http_proxy
    config:
      ## Proxy host details
      host: 0.0.0.0
      protocol: http
      port: 8181

      ## Proxy target details
      proxy_host: 0.0.0.0
      proxy_port: 8282
      proxy_protocol: https

      ## Certificate to present to Muxy clients (i.e. server certs)
      proxy_ssl_key: proxy-server/test.key
      proxy_ssl_cert: proxy-server/test.crt

      ## Certificate to present to Muxy proxy targets (i.e. client certs)
      proxy_client_ssl_key: client-certs/cert-key.pem
      proxy_client_ssl_cert: client-certs/cert.pem
      proxy_client_ssl_ca: client-certs/ca.pem

      ## Enable this to proxy targets we don't trust
      # insecure: true # allow insecure https

      # Specify additional proxy rules. Default catch-all proxy still
      # applies with lowest matching precedence.
      # Request matchers are specified as valid regular expressions
      # and must be properly YAML escaped.
      # See https://github.com/mefellows/muxy/issues/11 for behaviour.
      - request:
          method: 'GET|DELETE'
          path: '^\/foo'
          host: '.*foo\.com'
        pass:
          path: '/bar'
          scheme: 'http'
          host: 'bar.com'

Simple TCP Proxy that starts up on a local IP/Hostname and Port, forwarding traffic to the specified proxy_host on proxy_port.

Example configuration snippet:

proxy:
  - name: tcp_proxy
    config:
      host: 0.0.0.0 # Local ip/hostname to bind to and accept connections.
      port: 8080 # Local port to bind to
      proxy_host: 0.0.0.0
      proxy_port: 2000
      nagles_algorithm: true
      packet_size: 64

Middleware have the ability to intervene upon receiving a request (Pre-Dispatch) or before sending the response back to the client (Post-Dispatch). In some cases, such as the Network Shaper, the effect is applied before any request is made (e.g. if the local network device configuration is altered).

A basic middleware that simply adds a delay of delay milliseconds to the request or response.

Example configuration snippet:

middleware:
  - name: delay
    config:
      request_delay: 1000 # Delay in ms to apply to request to target
      response_delay: 500 # Delay in ms to apply to response from target

      # Specify additional matching rules. Default is to apply delay to all
      # requests on all http proxies.
      # Request matchers are specified as valid regular expressions
      # and must be properly YAML escaped.
      # See https://github.com/mefellows/muxy/issues/11 for behaviour.
      matching_rules:
        - method: "GET|DELETE"
          path: "^/boo"
          host: 'foo\.com'

A Layer 7 tamperer, this plugin allows you to modify response headers, status code or the body itself.

Example configuration snippet:

middleware:
  - name: http_tamperer
    config:
      request:
        host: "somehost" # Override Host header that's sent to target
        path: "/" # Override the request path
        method: "GET" # Override request method
        headers:
          x_my_request: "foo" # Override request header
          content_type: "application/x-www-form-urlencoded"
          content_length: "5"
        cookies: # Custom request cookies
          - name: "fooreq"
            value: "blahaoeuaoeu"
            domain: "localhost"
            path: "/foopath"
            secure: true
            rawexpires: "Sat, 12 Sep 2015 09:19:48 UTC"
            maxage: 200
            httponly: true
        body: "wow, new body!" # Override request body
      response:
        status: 201 # Override HTTP Status code
        headers: # Override response headers
          content_length: "27"
          x_foo_bar: "baz"
        body: "my new body" # Override response body
        cookies: # Custom response cookies
          - name: "foo"
            value: "blahaoeuaoeu"
            domain: "localhost"
            path: "/foopath"
            secure: true
            rawexpires: "Sat, 12 Sep 2015 09:19:48 UTC"
            maxage: 200
            httponly: true

      # Specify additional matching rules. Default is to apply delay to all
      # requests on all http proxies.
      # Request matchers are specified as valid regular expressions
      # and must be properly YAML escaped.
      # See https://github.com/mefellows/muxy/issues/11 for behaviour.
      matching_rules:
        - method: "GET|DELETE"
          path: "^/boo"
          host: 'foo\.com'

The network shaper plugin is a Layer 4 tamperer, and requires root access to work, as it needs to configure the local firewall and network devices. Using the excellent Comcast library, it can shape and interfere with network traffic, including bandwidth, latency, packet loss and jitter on specified ports, IPs and protocols.

NOTE: This component only works on MacOSX, FreeBSD, Linux and common *nix flavours.

Example configuration snippet:

middleware:
  - name: network_shape
    config:
      latency: 250 # Latency to add in ms
      target_bw: 750 # Bandwidth in kbits/s
      packet_loss: 0.5 # Packet loss, as a %
      target_ips: # Target ipv4 IP addresses
        - 0.0.0.0
      target_ips6: # Target ipv6 IP addresses
        - "::1/128"
      target_ports: # Target destination ports
        - "80"
      target_protos: # Target protocols
        - "tcp"
        - "udp"
        - "icmp"
      device: "lo" # defaults to eth0

The TCP Tamperer is a Layer 5 tamperer, modifying the messages in and around TCP sessions. Crudely, you can set the body of inbound and outbound TCP packets, truncate the last character of messages or randomise the text over the wire.

- name: tcp_tamperer
  config:
    request:
      body: "wow, new request!" # Override request body
      randomize: true # Replaces input message with a random string
      truncate: true # Removes last character from the request message
    response:
      body: "wow, new response!" # Override response body
      randomize: true # Replaces response message with a random string
      truncate: true # Removes last character from the response message

Log the in/out messages, optionally requesting the output to be hex encoded.

Example configuration snippet:

middleware:
  - name: logger
    config:
      hex_output: false # Display output as Hex instead of a string

Refer to the example YAML file for a full reference.

Using the Hystrix Go library, we use Muxy to trigger a circuit breaker and return a canned response, ensuring we don't have downtime. View the example.

Download the Docker image by running:

docker pull mefellows/muxy

After creating a [config](#configuration-reference] file (let's assume it's at ./conf/config.yml), and assuming you are proxying something on port 80, you can now run the image locally:

docker run \
  -d \
  -p 80:80 \
  -v "$PWD/conf":/opt/muxy/conf \
  --privileged \
  mefellows/muxy

You should now be able to hit this Docker container and simulate any failures as per usual. e.g. curl docker:80/some/endpoint.

The Hystrix example above has a detailed example on how to use Muxy with a more complicated system, using Docker Compose to orchestrate a number of containers.

Muxy is built as a series of configurable plugins (using Plugo) that must be specified in the configuration file to be activated. Start with a quick tour of Plugo before progressing.

Proxies must implement the Proxy interface, and register themselves via PluginFactories.register to be available at runtime. Take a look at the HTTP Proxy for a good working example.

Middlewares implement the Middleware interface and register themselves via PluginFactories.register to be available at runtime. Take a look at the HTTP Delay for a good working example.

See CONTRIBUTING.