./fabio

Current version: 1.0.5

fabio is a fast, modern, zero-conf load balancing HTTP(S) router for deploying microservices managed by consul.

Why build another HTTP router?

Both hardware and software routers like Citrix Netscaler, F5 Big IP, haproxy, varnish, nginx or apache require some form of configuration - the routing table - to route incoming traffic to services which can handle them. The routing table has to be kept in sync with the actual deployed set of services and instances during each deployment and each outage on every environment. This makes the routing table a crucial part of the configuration without the application cannot function.

Managing the routing table can be automated via API calls or tools like consul-template but that also requires configuration and/or tools. In the case of consul-template the config file template itself has to be kept in sync with the actual setup of the application. Finally, updating the routing table without loss of existing connections can be [challenging](http://engineeringblog.yelp.com/2015/04/true- zero-downtime-haproxy-reloads.html).

fabio solves this problem by making the services themselves responsible for updating the routing table. Services already know which routes they serve since they have handlers who can handle requests for them. Once services push the routes they handle into the service registry (in this case consul) fabio can build the routing table and can re-configure itself on every change automatically without restart and without the loss of existing connections.

The motivation is also outlined in the presentation I've given at the dotGo EU pre-party in Paris on 9 Nov 2015. You can watch it here.

fabio was developed at the eBay Classifieds Group in Amsterdam and routes traffic for marktplaats.nl and kijiji.it. Marktplaats is running all of its traffic through fabio which is several thousand requests per second distributed over several fabio instances. We don't observe any measurable additional latency.

Features

• Single binary in Go. No external dependencies.
• Zero-conf
• Hot-reloading of routing table through backend watchers
• Round robin and random distribution
• Traffic Shaping (send 5% of traffic to new instances)
• Graphite metrics
• Request tracing
• WebUI
• Fast
• v1.0.4: SSL client certificate authentication support (see proxy.addr in fabio.properties)
• v1.0.5: X-Forwarded-For and Forwarded header support
• v1.0.5: Websocket support (experimental)

Documentation

• Installation
• Quickstart
• Deployment
• Configuration (documented fabio.properties file)
• Performance
• Service configuration
• Manual overrides
• Routing
• Traffic shaping
• Websockets
• Debugging
• Request tracing
• Web UI
• Changelog
• License

Quickstart

This is how you use fabio in your setup:

1. Register your service in consul
2. Register a health check in consul as described here. Make sure the health check is passing since fabio will only watch services which have a passing health check.
3. Register one urlprefix- tag per host/path prefix it serves, e.g. urlprefix-/css, urlprefix-/static, urlprefix-mysite.com/
4. Start fabio without a config file (assuming a consul agent on localhost:8500) Watch the log output how fabio picks up the route to your service. Try starting/stopping your service to see how the routing table changes instantly.
5. Send all your HTTP traffic to fabio on port 9999
6. Done

To start a sample server to test the routing run the demo/server like this:

./server -addr 127.0.0.1:5000 -name svc-a -prefix /foo

and access the server direct and via fabio

curl 127.0.0.1:5000/foo   # direct
curl 127.0.0.1:9999/foo   # via fabio

If you want fabio to handle SSL as well set the proxy.addr along with the public/private key files in fabio.properties and run fabio -cfg fabio.properties. You might also want to set the proxy.header.clientip, proxy.header.tls and proxy.header.tls.value options.

Check the Debugging section to see how to test fabio with curl.

See fabio in action

[](https://www.youtube.com/watch?v=gvxxu0PLevs"fabio demo - Click to Watch!")

The fabio-example project is now in the demo/server directory.

Installation

To install fabio run (you need Go 1.4 or higher)

go get github.com/eBay/fabio

To start fabio run

./fabio

which will run it with the default configuration which is described in fabio.properties. To run it with a config file run it with

./fabio -cfg fabio.properties

or use the official Docker image and mount your own config file to /etc/fabio/fabio.properties

docker run -d -p 9999:9999 -p 9998:9998 -v $PWD/fabio/fabio.properties:/etc/fabio/fabio.properties magiconair/fabio

If you want to run the Docker image with one or more SSL certificates then you can store your configuration and certificates in /etc/fabio and mount the entire directory, e.g.

$ cat ~/fabio/fabio.properties
proxy.addr=:443;/etc/fabio/ssl/mycert.pem;/etc/fabio/ssl/mykey.pem

docker run -d -p 443:443 -p 9998:9998 -v $PWD/fabio:/etc/fabio magiconair/fabio

The official Docker image contains the root CA certificates from a recent and updated Ubuntu 12.04.5 LTS installation.

Deployment

The main use-case for fabio is to distribute incoming HTTP(S) requests from the internet to frontend (FE) services which can handle these requests. In this scenario the FE services then use the service discovery feature in consul to find backend (BE) services they need in order to fulfil the request.

That means that fabio is currently not used as an FE-BE or BE-BE router to route traffic among the services themselves since the service discovery of consul already solves that problem. Having said that, there is nothing that inherently prevents fabio from being used that way. It just means that we are not doing it.

Direct

In the following setup fabio is configured to listen on the public ip(s) where it can optionally terminate SSL traffic for one or more domains - one ip per domain.

                                           +--> service-a
                                           |
internet -- HTTP/HTTPS --> fabio -- HTTP --+--> service-b
                                           |
                                           +--> service-c

To scale fabio you can deploy it together with the frontend services which provides high-availability and distributes the network bandwidth.

           +- HTTP/HTTPS -> fabio -+- HTTP -> service-a (host-a)
           |                       |
internet --+- HTTP/HTTPS -> fabio -+- HTTP -> service-b (host-b)
           |                       |
           +- HTTP/HTTPS -> fabio -+- HTTP -> service-c (host-c)

Behind an existing LB/Gateway

In the following setup fabio is configured receive all incoming traffic from an existing gateway which also terminates SSL for one or more domains. fabio supports SSL Client Certificate Authentication to support the Amazon API Gateway

                                                          +--> service-a
                                                          |
internet -- HTTP/HTTPS --> LB -- HTTP --> fabio -- HTTP --+--> service-b
                                                          |
                                                          +--> service-c

Again, to scale fabio you can deploy it together with the frontend services which provides high-availability and distributes the network bandwidth.

                               +- HTTP -> fabio -+-> service-a (host-a)
                               |                 |
internet -- HTTP/HTTPS --> LB -+- HTTP -> fabio -+-> service-b (host-b)
                               |                 |
                               +- HTTP -> fabio -+-> service-c (host-c)

Performance

fabio has been tested to deliver up to 15.000 req/sec on a single 16 core host with moderate memory requirements (~ 60 MB).

To achieve the performance fabio sets the following defaults which can be overwritten with the environment variables:

• GOMAXPROCS is set to runtime.NumCPU() since this is not the default for Go 1.4 and before
• GOGC=800 is set to reduce the pressure on the garbage collector

When fabio is compiled with Go 1.5 and run with default settings it can be up to 40% slower than the same version compiled with Go 1.4. The GOGC=100 default puts more pressure on the Go 1.5 GC which makes the fabio spend 10% of the time in the GC. With GOGC=800 this drops back to 1-2%. Higher values don't provide higher gains.

As usual, don't rely on these numbers and perform your own benchmarks. You can check the time fabio spends in the GC with GODEBUG=gctrace=1.

Service configuration

Each service can register one or more URL prefixes for which it serves traffic. A URL prefix is a host/path combination without a scheme since SSL has already been terminated and all traffic is expected to be HTTP. To register a URL prefix add a tag urlprefix-host/path to the service definition.

By default, traffic is distributed evenly across all service instances which register a URL prefix but you can set the amount of traffic a set of instances will receive ("Canary testing"). See [Traffic Shaping](#Traffic Shaping) below.

A background process watches for service definition and health status changes in consul. When a change is detected a new routing table is constructed using the commands described in [Config Commands](#Config Commands).

Manual overrides

Since an automatically generated routing table can only be changed with a service deployment additional routing commands can be stored manually in the consul KV store which get appended to the automatically generated routing table. This allows fine-tuning and fixing of problems without a deployment.

The [Traffic Shaping](#Traffic Shaping) commands are also stored in the KV store.

Routing Table Configuration

The routing table is configured with the following commands:

route add service host/path targetURL [weight <weight>] [tags "tag1,tag2,..."]
	- Add a new route for host/path to targetURL

route del service
	- Remove all routes for service

route del service host/path
	- Remove all routes for host/path for this service only

route del service host/path targetURL
	- Remove only this route

route weight service host/path weight n tags "tag1,tag2"
  - Route n% of traffic to services matching service, host/path and tags
    n is a float > 0 describing a percentage, e.g. 0.5 == 50%
    n <= 0: means no fixed weighting. Traffic is evenly distributed
    n > 0: route will receive n% of traffic. If sum(n) > 1 then n is normalized.
    sum(n) >= 1: only matching services will receive traffic

The order of commands matters but routes are always ordered from most to least specific by prefix length.

Routing

The routing table contains first all routes with a host sorted by prefix length in descending order and then all routes without a host again sorted by prefix length in descending order.

For each incoming request the routing table is searched top to bottom for a matching route. A route matches if either host/path or - if there was no match - just /path matches.

The matching route determines the target URL depending on the configured strategy. rnd and rr are available with rnd being the default.

Example

The auto-generated routing table is

route add service-a www.mp.dev/accounts/ http://host-a:11050/ tags "a,b"
route add service-a www.kjca.dev/accounts/ http://host-a:11050/ tags "a,b"
route add service-a www.dba.dev/accounts/ http://host-a:11050/ tags "a,b"
route add service-b www.mp.dev/auth/ http://host-b:11080/ tags "a,b"
route add service-b www.kjca.dev/auth/ http://host-b:11080/ tags "a,b"
route add service-b www.dba.dev/auth/ http://host-b:11080/ tags "a,b"

The manual configuration under /fabio/config is

route del service-b www.dba.dev/auth/
route add service-c www.somedomain.com/ http://host-z:12345/

The complete routing table then is

route add service-a www.mp.dev/accounts/ http://host-a:11050/ tags "a,b"
route add service-a www.kjca.dev/accounts/ http://host-a:11050/ tags "a,b"
route add service-a www.dba.dev/accounts/ http://host-a:11050/ tags "a,b"
route add service-b www.mp.dev/auth/ http://host-b:11080/ tags "a,b"
route add service-b www.kjca.dev/auth/ http://host-b:11080/ tags "a,b"
route add service-c www.somedomain.com/ http://host-z:12345/ tags "a,b"

Traffic Shaping

fabio allows to control the amount of traffic a set of service instances will receive. You can use this feature to direct a fixed percentage of traffic to a newer version of an existing service for testing ("Canary testing").

The following command will allocate 5% of traffic to www.kjca.dev/auth/ to all instances of service-b which match tags version-15 and dc-fra. This is independent of the number of actual instances running. The remaining 95% of the traffic will be distributed evenly across the remaining instances publishing the same prefix.

route weight service-b www.kjca.dev/auth/ weight 0.05 tags "version-15,dc-fra"

Websockets

Websocket support works but is considered experimental since I don't have an in-house use case for it at the moment. I would like to hear from users whether it works in their environments beyond my simple test case before I declare it stable. It has been implemented with the websocket library from golang.org/x/net/websocket

You can test the websocket support with the demo/wsclient and demo/server which implements a simple echo server.

./server -addr 127.0.0.1:5000 -name ws-a -prefix /echo -proto ws
./wsclient -url ws://127.0.0.1:9999/echo

You can also run multiple web socket servers on different ports but the same endpoint.

fabio detects on whether to forward the request as HTTP or WS based on the value of the Upgrade header. If the value is websocket it will attempt a websocket connection to the target. Otherwise, it will fall back to HTTP.

One limitation of the current implementation is that the accepted set of protocols has to be symmetric across all services handling it. Only the following combinations will work reliably:

svc-a and svc-b register /foo and accept only HTTP traffic there
svc-a and svc-b register /foo and accept only WS traffic there
svc-a and svc-b register /foo and accept both HTTP and WS traffic there

The following setup (or variations thereof) will not work reliably:

svc-a registers /foo and accept only WS traffic there
svc-b registers /foo and accept only HTTP traffic there

This is not a limitation of the routing itself but because the current configuration does not provide fabio with enough information to make the routing decision since the services do not advertise the protocols they handle on a given endpoint.

This does not look like a big restriction but is also not difficult to extend in a later version assuming there are use cases which require this behavior. For now the services have to be symmetric in the protocols they accept.

Debugging

To send a request from the command line via the fabio using curl you should send it as follows:

curl -v -H 'Host: foo.com' 'http://localhost:9999/path'

The -x or --proxy options will most likely not work as you expect as they send the full URL instead of just the request URI which usually does not match any route but the default one - if configured.

Request tracing

To trace how a request is routed you can add a Trace header with an non- empty value which is truncated at 16 characters to keep the log output short.

$ curl -v -H 'Trace: abc' -H 'Host: foo.com' 'http://localhost:9999/bar/baz'

2015/09/28 21:56:26 [TRACE] abc Tracing foo.com/bar/baz
2015/09/28 21:56:26 [TRACE] abc No match foo.com/bang
2015/09/28 21:56:26 [TRACE] abc Match foo.com/
2015/09/28 22:01:34 [TRACE] abc Routing to http://1.2.3.4:8080/

Web UI

fabio contains a (very) simple web ui to examine the routing table. By default it is accessible on http://localhost:9998/

License

MIT licensed