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Dynamic service configuration

This Go package provides a dynamic service configuration backed by etcd, so there should be no need to redeploy a service to change its settings.

For example, project Curiosity expects settings such as velocity = 10 and is_camera_enabled = true. Let's save them in etcd with a path prefix /configs/curiosity/.

$ brew install etcd
$ etcd
$ etcdctl put /configs/curiosity/velocity 10
OK
$ etcdctl put /configs/curiosity/is_camera_enabled true
OK

On the service side the settings are fetched from the same path.

const defaultVelocity = 5

c, err := dynconf.New("/configs/curiosity/")
if err != nil {
	// No worries if etcd is down, the rover can still roll with the default settings.
}
defer c.Close()

rover.SetVelocity(
	c.Int("velocity", defaultVelocity),
)

Testing

Run etcd (127.0.0.1:2379 by default) and then launch the tests.

$ etcd
$ go test -count=1 .

Toxiproxy

With Toxiproxy you can simulate network conditions. All communication with the Toxiproxy daemon from the client happens via HTTP on port 8474.

$ brew install toxiproxy
$ toxiproxy-server
INFO[0000] API HTTP server starting                      host=localhost port=8474 version=2.2.0

Create a proxy called dynconf_etcd that listens on port 22379 and proxies traffic to etcd running on 2379 port.

$ toxiproxy-cli create --listen localhost:22379 --upstream localhost:2379 dynconf_etcd
Created new proxy dynconf_etcd
$ toxiproxy-cli list
Name			Listen		Upstream		Enabled		Toxics
======================================================================================
dynconf_etcd		127.0.0.1:22379	localhost:2379		enabled		None

Check that etcd is reachable via Toxiproxy.

$ etcdctl --endpoints=127.0.0.1:22379 get /configs/curiosity/velocity
OK

Add 1500ms downstream latency.

$ toxiproxy-cli toxic add --type latency --attribute latency=1500 dynconf_etcd
$ toxiproxy-cli inspect dynconf_etcd
Name: dynconf_etcd	Listen: 127.0.0.1:22379	Upstream: localhost:2379
======================================================================
Upstream toxics:
Proxy has no Upstream toxics enabled.

Downstream toxics:
latency_downstream:	type=latency	stream=downstream	toxicity=1.00	attributes=[	jitter=0	latency=5000	]

There should be 1.5s latency introduced. You can remove latency_downstream afterwards.

$ etcdctl --endpoints=127.0.0.1:22379 get /configs/curiosity/velocity
OK
$ toxiproxy-cli toxic remove -n latency_downstream dynconf_etcd
Removed toxic 'latency_downstream' on proxy 'dynconf_etcd'

There are more toxics available. For example, stop all data from getting through, and close the connection after 10s.

$ toxiproxy-cli toxic add --type timeout --attribute timeout=10000 dynconf_etcd
Added downstream timeout toxic 'timeout_downstream' on proxy 'dynconf_etcd'
$ toxiproxy-cli toxic remove -n timeout_downstream dynconf_etcd

Simulate TCP RESET (Connection reset by peer) by closing connections after 10s.

$ toxiproxy-cli toxic add --type reset_peer --attribute timeout=10000 dynconf_etcd
Added downstream reset_peer toxic 'reset_peer_downstream' on proxy 'dynconf_etcd'
$ toxiproxy-cli toxic remove -n reset_peer_downstream dynconf_etcd