The document provides an overview of service discovery using Consul from HashiCorp, detailing its architecture, APIs, and features such as service health checks and multi-datacenter support. It discusses traditional problems in service discovery, solutions offered by Consul, and alternatives like Zookeeper and etcd. Additionally, it covers implementation strategies for service registration and client-side load balancing with examples and links to further resources.

1. Service Discovery like a Pro
Eran Harel
@eran_ha

2. ● Motivation
● Consul Overview
● Consul Architecture
● API
● Alternatives
● Discovery and Client Side LB Demo

3. Do we have a problem at all?

4. my.target.service.url=http://host:port/contextBase/...
memcached.cluster=mem1:11211,mem1:11311,mem2:11211,mem2:111311
db.host=mysql:3304
kafka.brokers=kafka1:9092,kafka2:9092,kafka3:9092
Hard Coded Topology...

5. ● What do we do if the nodes are dynamically allocated (e.g.
when using a scheduler a-la Mesos)?
● What do we do when the topology changes?
● What do we do if nodes become unhealthy?
● How can we scale (up/down) our clusters?
● What happens if the port is dynamic?
Why is Hard Coded Topology a problem?

6. The Traditional Approaches

7. ● HTTP Load Balancers (e.g. HAProxy)
● TCP Keepalive
● VIP
● etc...

8. What is Consul?

9. Service discovery and configuration
made easy. Distributed, highly
available, and datacenter-aware.

10. ● Developed @ Hashicorp
● Open source - https://github.com/hashicorp/consul
● Written in Go
● Current version 0.7.2
● https://consul.io/

11. ● Service Discovery
● Scalable Failure Detection (Distributed Health Checks)
● K/V Store
● Load Balancing
● Multi Datacenter
● consul-template (external project)
Features

12. Basic Architecture

13. Consul APIs

14. DNS API

15. DNS API
$ host memcached.service.consul
memcached.service.consul has address 10.xx.xx.01
memcached.service.consul has address 10.xx.xx.02
memcached.service.consul has address 10.xx.xx.03
$
$ host test.memcached.service.consul
memcached.service.consul has address 10.xx.xx.51
memcached.service.consul has address 10.xx.xx.52
$
$ host prod.memcached-legacy.service.dc2.consul
memcached.service.consul has address 10.yy.xx.01
memcached.service.consul has address 10.yy.xx.02

16. REST API
● http://localhost:8500/v1/agent/service/register
● http://localhost:8500/v1/agent/service/deregister/<MyService>
● http://localhost:8500/v1/catalog/services/service/<MyService>
● http://localhost:8500/v1/catalog/nodes
● http://localhost:8500/v1/health/service/<MyService>
● Certain endpoints support a feature called a "blocking query." A blocking query is
used to wait for a potential change using long polling.

17. Consul CLI
$ consul
usage: consul [--version] [--help] <command> [<args>]
Available commands are:
agent Runs a Consul agent
configtest Validate config file
event Fire a new event
exec Executes a command on Consul nodes
force-leave Forces a member of the cluster to enter the "left" state
info Provides debugging information for operators
join Tell Consul agent to join cluster
keygen Generates a new encryption key
keyring Manages gossip layer encryption keys
leave Gracefully leaves the Consul cluster and shuts down
lock Execute a command holding a lock
maint Controls node or service maintenance mode
members Lists the members of a Consul cluster
monitor Stream logs from a Consul agent
reload Triggers the agent to reload configuration files
rtt Estimates network round trip time between nodes
version Prints the Consul version
watch Watch for changes in Consul

18. Consul CLI (cont)
$ consul maint -service Hello0 -enable
Service maintenance is now enabled for "Hello0"
On the server log:
2015/12/09 21:51:13 [INFO] agent: Service "Hello0" entered maintenance mode
2015/12/09 21:51:13 [INFO] agent: Synced check '_service_maintenance:Hello0'

19. What are the alternatives?
● ZooKeeper, doozerd, etcd
● Chef, Puppet, etc
● Nagios, Sensu
● SkyDNS
● SmartStack
● Serf

20. Implementing Service Discovery

21. How do we implement discovery and client side LB?
Each module registers itself to the local consul agent upon startup, and provides
enough metadata to allow filtering
http://localhost:8500/v1/register
{
"ID": "Hello0",
"Name": "Hello",
"Port": 8080,
"Tags": [
"instance0",
"production",
"httpPort-8080",
"contextPath-/api",
],
"Check": {
"HTTP": "http://localhost:8080/api/hello/instance",
"Interval": "1s",
"Timeout”: "1s"
}
}

22. How do we implement discovery and client side LB?
The local consul agent calls the provided health check(s) and verifies the instances are
healthy.
Don’t forget to add proper timeouts!
curl --fail --max-time 1 “http://localhost:8080/api/hello/instance”

23. How do we implement discovery and client side LB?
Clients perform long polling queries to the health API, maintain a list of healthy
instances, and build target URLs.
At Outbrain we use the ConsulBasedTargetProvider with HealthTargetsList
to achieve this.
http://localhost:8500/v1/health/service/Hello?passing=true&tag=production&stale=true&
index={index}&wait=30s
X-Consul-Index=4245721

24. How do we implement discovery and client side LB?
Upon client request, we select a target based on some strategy (e.g. round-robin).

25. How do we implement discovery and client side LB?
Clients need to implement resilience logic such as retries, timeouts, circuit-breakers,
etc
final HelloService helloService = new ClientBuilder<>(HelloService.class).
setProtocol(ContentType.JSON).
setConnectionTimeout(100).
setRequestTimeout(100).
setRetries(3).
setTargetProvider(new ConsulBasedTargetProvider(healthyTargetsList, "/hello", null)).
build();

26. Discovery and Client Side LB Demo

27. Hello2
Hello1
http://localhost:8500/v1/register
{
"ID": "Hello0",
"Name": "Hello",
"Port": 8080,
"Tags": [
"instance0",
"production",
"httpPort-8080",
"contextPath-/api",
],
"Check": {
"HTTP": "http://localhost:8080/api/hello/instance",
"Interval": "1s",
"Timeout”: "1s"
}
}
http://localhost:8500/v1/health/service/Hello
?passing=true&tag=production&stale=true
&index={index}&wait=30s
Demo Preview
Hello0 :8080
:8081
:8082
Register
Call service

28. References & Links
● Consul Docs - https://consul.io/docs/index.html
● Example Source Code -
https://github.com/outbrain/ob1k/tree/master/ob1k-example/src/main/java/com/ou
tbrain/ob1k/example/hello

29. We are recruiting...
http://www.outbrain.com/about/careers