GOV.UK Router
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README.md

router

This is a HTTP reverse proxy router built on top of triemux. It loads a routing table into memory from a MongoDB database and acts as a:

  • Reverse proxy, forwarding requests to and serving responses from multiple backend servers on a single domain.
  • Redirector, serving HTTP 301 and 302 redirects to new URLs.
  • Gone responder, serving HTTP 410 responses for resources that used to but no longer exist.

The sister project router-api provides a read/write interface to the underlying database and route reloading.

Environment assumptions

Our usage of router places it behind and in front of Nginx and/or Varnish.

As such, there are some things that we are guarded against:

  • Response buffering for slow clients
  • Basic request sanitisation

And some features that we have no need to implement:

  • Access logging (but error logging is implemented)
  • SSL
  • Health check probes
  • Custom header mangling
  • Response rewriting
  • Authentication

Build

If you have a working Go development setup, you should be able to run:

go install github.com/alphagov/router
$GOPATH/bin/router -h

If you've just checked out this repository and have the go tool on your $PATH, you can just build the router in-place:

go build

Tests

You can run all tests with the shell script used by CI:

./jenkins.sh

The trie and triemux sub-packages have unit tests and benchmarks written in Go's own testing framework. To run them:

go test -bench=. ./trie ./triemux

The router itself doesn't really benefit from having unit tests around individual functions. Instead it has a comprehensive set of integration tests to exercise it's HTTP handling, error reporting, and performance. These are written/orchestrated in Ruby rspec and deliberately agnostic of the Go code beneath.

These require a local MongoDB instance and can be run with:

bundle exec rspec

Some of the integration tests are optional because they have certain environment requirements that make them unfeasible to run within CI.

Data structure

The Router requires two MongoDB collections: routes and backends.

Routes

The routes collection uses the following data structure:

{
  "_id"           : ObjectId(),
  "route_type"    : ["prefix","exact"],
  "incoming_path" : "/url-path/here",
  "handler"       : ["backend", "redirect", "gone"],
}

The behaviour is determined by handler. See below for extra fields corresponding to handler types.

backend handler

The backend handler causes the Router to reverse proxy to a named backend. The following extra fields are supported:

{
  "backend_id" : "backend-id-corresponding-to-backends-collection"
}

redirect handler

The redirect handler causes the Router to redirect the given incoming_path to the path stored in redirect_to. The following extra fields are supported:

{
  "redirect_to"   : "/target-of-redirect",
  "redirect_type" : ["permanent", "temporary"]
}

gone handler

The gone handler causes the Router to return a 410 response.

Backends

The backends collection uses the following data structure:

{
  "_id"         : ObjectId(),
  "backend_id"  : "arbitrary-slug-or-name",
  "backend_url" : "https://example.com:port/"
}

License

router is released under the MIT license, a copy of which can be found in LICENSE.