A collection of service discovery utils for DC/OS

DC/OS comes with a set of powerful yet un-opinionated service discovery mechanisms. While powerful, it can sometimes be hard for newcomers to quickly get results, so here a few tips and tricks in the following.

Prerequisites

1. Many shell commands below assume you've got jq installed.
2. All bash shell commands below assume that you've added your private SSH key already; if you haven't done this yet do the following: $ ssh-add ~/.ssh/MYPRIVATEKEY

1. Using the DC/OS command line interface

IP address of node a Marathon app is running on

Let's say you have a Marathon app with the app ID /example and want to know on the public routable IP address it is running (if it's on a public node):

$ export APP_NODE=$(echo "curl -s ifconfig.ca" | dcos node ssh --master-proxy --mesos-id=$(dcos task --json | jq --raw-output '.[] | select(.name == "example") | .slave_id') 2>/dev/null)

Listing public nodes

To get the cluster-internal IP address of the public node:

$ export PUBLIC_NODE_INTERNAL_IP=$(dcos node --json | jq "map(select(.attributes.public_ip).hostname)" | grep \" | cut -d"\"" -f 2)

To get the public Internet-routable IP address of the public node:

$ export PUBLIC_NODE_PUBLIC_IP=$(echo "curl -s ifconfig.ca" | dcos node ssh --master-proxy --mesos-id=$(dcos node --json | jq --raw-output '.[] | select(.reserved_resources.slave_public != null) | .id') 2>/dev/null)

Manual service discovery

To get the (cluster-internal) IP address and port of a Marathon app:

$ export APP_ENDPOINT=$(dcos marathon task list --json | jq "map(select(.appId==\"/peek\").host, select(.appId==\"/peek\").ports)") 

Using the same base command, manual:

$ dcos marathon task list
APP       HEALTHY  STARTED                   HOST       ID
/example  True     2016-04-22T13:00:57.458Z  10.0.3.34  example.3459106a-088a-11e6-ba3b-9eefd772c507

$ dcos marathon task show example.3459106a-088a-11e6-ba3b-9eefd772c507 | jq .host,.ports
"10.0.3.34"
[
  31105
]

Or, alternatively, using a different sub-command:

$ export APP_ENDPOINT=$(dcos marathon app show peek | jq .tasks[0].host,.tasks[0].ports[0])

2. Using dig

Assuming you want a Marathon app with the ID /example and you have dig installed. Then you can—from within the cluster, that is, after SSHing into a node—do the following:

$ app_port=$(dig _peek._tcp.marathon.mesos SRV | grep ^_peek._tcp.marathon.mesos. | cut -d " " -f 4)
$ app_ip=$(dig _peek._tcp.marathon.mesos SRV | grep ^$(dig _peek._tcp.marathon.mesos SRV | grep ^_peek._tcp.marathon.mesos. | cut -d " " -f 5) | cut -d " " -f 3 | cut -d$'\t' -f 3)
$ export APP_ENDPOINT=$app_ip:$app_port

3. Programming Languages

In Go

type SRVRecord struct {
	Service string
	Host    string
	IP      string
	Port    string
}

func serviceDiscovery(lookup string) string {
	mesosdns := "http://leader.mesos:8123" // the Mesos-DNS HTTP API within the cluster
	query := "_" + lookup + "._tcp.marathon.mesos."
	resp, err := http.Get(mesosdns + "/v1/services/" + query)
	if err != nil {
		log.Fatalf("Can't look up my address due to %v", err)
	}
	defer resp.Body.Close()
	body, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		log.Fatalf("Error reading response from Mesos-DNS due to %v", err)
	}
	var srvrecords []SRVRecord
	err = json.Unmarshal(body, &srvrecords)
	if err != nil {
		log.Fatalf("Error decoding JSON object due to %v", err)
	}
	return "http://" + srvrecords[0].Host + ":" + srvrecords[0].Port
}

In JavaScript

• front-end of the m-shop: See the example.
• mesosdns-cli: A CLI for querying Mesos DNS service names.
• mesosdns-client: A simple client for Mesos DNS which makes it possible to receive actual endpoints from Mesos service names.
• mesosdns-http-agent: A http.Agent which makes it possible to consume Mesos service resources by simply using the Mesos DNS service names.

In Bash scripting

• tobilg/mesosdns-resolver: A bash script to resolve Mesos DNS SRV records to actual host:port endpoints

A Python snippet

See the mc project.